Java Interview Questions Basic Coding For Freshers{New 2023}

What We Are Learn:

Java Interview Questions Core Java: Java is one of the most popular programming languages today, with a wide range of applications in web development, mobile app development, and enterprise software development. As a result, many companies seek skilled Java developers to join their teams, and job seekers must be prepared to answer various technical questions during the interview process.

Java is a versatile language used for over two decades, and its popularity has only grown over time. One of the key reasons for this is Java’s platform independence, which means that code written in Java can be executed on any platform, from desktop computers to mobile devices to web servers. This makes Java a favorite among developers, who appreciate the ease of use and versatility that the language provides.

However, with the growing demand for skilled Java developers, job interviews have become increasingly competitive, and employers are looking for candidates who deeply understand the language and its related technologies. To succeed in a Java interview, candidates must have a solid grasp of the fundamentals and the ability to apply these concepts to real-world scenarios.

In addition to technical skills, successful candidates must also be able to communicate effectively and demonstrate a passion for programming. Employers are looking for candidates who are motivated to learn and improve and enthusiastic about working in a team environment.

To help candidates prepare for Java interviews, this article will explore some common Java interview questions and tips and strategies for answering them effectively. By reviewing these questions and practicing your responses, you can gain the confidence you need to excel in your next Java interview and land your dream job in this exciting and rewarding field.

Java Interview Questions

List Any Five Features Of Java.
Why Is Java Considered Dynamic?
Define Class.
Define JVM, JDK And JRE?
Define The Java’s Wora Nature.
What Is Abstraction?
What Is Encapsulation?
Can We Override A Static Method Or a Main Method?
What Is The Method Of Hiding?
What Is the Difference between Comparable And Comparator?
What Is Treeset?
What Is Dictionary In Java?
Why Is Java Known As The Platform Independent Programming Language?
Name The Data Types That Java supports.
Throw Some Light On The Main Features Of Java.
Define Autoboxing And Unboxing.
What Are Overloading And Overriding In Java?
What Is Constructor Chaining In Java?
Explain Java Heap Space And Garbage Collection.
What Is The Difference Between Final, Finalize, And Finally?
What Is Wrapper Class?
What Is An Immutable Class?
What Is Array?
What Is String? What is the difference Between StringBuilder And Strinngbuffer?
What Is Function?
What Is Class?
What Is Object?
What Is Polymorphism?
What Is Function Overloading?
What Is Function Overriding?
Why Use Super And This Keyword In Java?
What Is Inheritance?
Describe The Types Of Inheritance.
What Is Scope? Describe The Types Of Scope.
Types Of Access Specifiers?
What Is Encapsulation?
What Is Abstraction?
Is There Any Difference Between A = A + B And A += B Expressions?
What Does The Expression 1.0 / 0.0 Return? Will There Be Any Compilation Errors?
Can We Use Multiple Main Methods In Multiple Classes?
Does Java Allow You To Override A Private Or Static Method?
What Happens When You Put A Key Object In A Hashmap That Is Already Present?
How Can You Determine If Jvm Is 32-bit Or 64-bit From Java Program?
What Is The Right Data Type To Represent Money (Like Dollar/pound) In Java?
How Can You Do Multiple Inheritances In Java?
How Can You Access A Non-static Variable From The Static Context?
Let’s Say There Is A Method That Throws Nullpointerexception In The Superclass. Can We Override It With A Method That Throws Runtimeexception?
How Can You Mark An Array Volatile In Java?
What Is The Difference Between Sleep() And Wait() Methods In Java?
Can You Create An Immutable Object That Contains A Mutable Object?
How Can You Convert An Array Of Bytes To a String?
What Is the Difference Between Cyclic Barrier And Countdownlatch Class?
What Is The Difference Between StringBuffer And StringBuilder?
Which Class Contains Clone Method? Cloneable Or Object Class?
Can You Cast An Int Variable Into A Byte Variable? What Happens If The Value Of Int Is Larger Than Byte?
In Java, Can We Store A Double Value In A Long Variable Without Explicit Casting?
What Will This Return 5*0.1 == 0.5? True Or False?
Out Of An Int And Integer, Which One Takes More Memory?
Can We Use String In The Switch Case Statement In Java?
Can We Use Multiple Main Methods In the Same Class?
When Creating An Abstract Class, Is It A Good Idea To Call Abstract Methods Inside Its Constructor?
How Can You Do Constructor Chaining In Java?
How Can We Find The Memory Usage Of Jvm From Java Code?
What Is The Difference Between X == Y And X.equals(Y) Expressions In Java?
How Can You Guarantee That The Garbage Collection Takes Place?
What Is The Relation Between X.hashcode() Method And X.equals(Y) Method Of Object Class?
What Is A Compile-Time Constant In Java?
Explain The Difference Between Fail-fast And Fail-safe Iterators.
You Have A Character Array And A String. Which One Is More Secure To Store Sensitive Data (Like Password, Date Of Birth, Etc.)?
Why Do You Use Volatile Keyword In Java?
What Is The Difference Between Poll() And Remove() Methods Of Queue In Java?

Java Interview Questions Basic

What Is The Difference Between Jdk, Jre, And Jvm?
What Is The Difference Between An Inner Class And A Sub-class?
What Is the Final Keyword In Java? Give An Example.
What’s The Base Class In Java From Which All Classes Are Derived?
What Is A Platform?
What Is Classloader?
What Is The Static Method?
Can A Class Have Multiple Constructors?
What Is An Interface And Why Interface?
What Is An Abstract Class?
What Is The Difference Between Abstract Class And Interface And Concrete Class(Normal Class)
Why Abstract Class?
What Is Polymorphism?
What Are Overloading And Overriding?
Explain Static And Nonstatic Members.
What Is the Difference between Final, Finalize, And Finally?
What Is The Difference Between Equals And == Operator
What Is The Case When You Override Hashcode() And Equals()? What Problem Can Occur If We Don’t Override Hashcode() Method?
What Are Immutable Classes?
Mention The Access Specifiers Used In Java.
What Is Singleton In Java?
What Is Jdk?
Which Is The Latest Version Of Java?
What Is The Advantage Of Java?
Javac And Java Commands Are Available In Which Folder?
What Is The Signature Of The Main Method?
What Is A Keyword? List Some Keywords.
What Is An Identifier?
What Are Literals?
Java Is Platform Independent. Explain
What Is Jre?
What Is A Variable?
Mention All The Primitive Data Types In Java
What Are The Primitive Variables?
What Are Reference Variables?
What Is String In Java?
What Is The Method?
General Syntax For A Method?
What Is Method Overloading?
Why Method Overloading?
What Are The Members?
What Are Static Members?
What Are Nonstatic Members?
List Out The Differences Between Static And Non-static Members.
What Is An Object?
What Is A Class?
What Are Global Variables?
How Can You Access A Static Global Variable Of A Class?
How Can You Access Non-static Global Variables Of A Class
What Will Be The Default Value For Global Variables?
What Will Be The Default Value For Reference Variables?
What Is The Default Value For The Boolean Variable?
What Are The Differences Between Local And Global Variables?

Java Interview Questions Coding

Write a program to Reverse the Number
Write a program to count a duplicate character in a String
Write a program to count the number of the word in a String
Write a program to reverse the word of the Character
Write a program INPUT-I work in exilant, and the output-I know ni tnalixe;
Write a program to String is palindrome or not.
Write a program to reverse a number with and without the third variable.
Write a program to remove the duplicate element in Array.
Write a program to remove duplicate Characters in String.
Write a program to Bubble Sort.
Write a program to Insertion Sort.
Write a program to Selection Sort.
Write a program to Count vowels in a String.
Write a program to no is binary or not.
Write a program to no is factorial.
Write a program to Find the largest no in the Array
Write a program reverse number.
Write a program to find the second no of ArrayList
Write a program to Sort Array?
Write a program to find the number of vowels present and their count from the given input String.

Java Interview Questions On Oops

What Is The Oops Concept Or Opps Principle?
Java Is Fully Oops Language Or Not?
What Is Oops
List Out The Oops Concepts
All Oops Concepts In A Single Program. Explain Oops
What Is The Oop Principle, Where You Used Polymorphism In Your Project?
What Is The Benefit Of Volatile Variable
Provide Byte Datatype Default Value In Java
Explain Applet
Define Use Cases In Java
Jvm Is A Dependent Or Independent Platform
Difference Between Hashmap And Hash Set, Set And Linkedlist, ArrayList And Vector List, Linkedhash Set, And HashSet
Abstract And Interface
Throw And Throws
How To Split
Checked And Unchecked Exception
How To Work With Ajax Application
Why String Is Immutable
What Is The Return Type Of Getwindowhandles();
What Are The Types Of Assertion And What Is An Assertion In Java
Difference Between Interface And Abstract Classes
What Is A Static Variable
What Is Volatile
What Is Transient
What Is The Difference Between Final, Finalize, And Finally
What Is The Difference Between Public, Private, And Protected
What Is Static?
What Is An Interface?
What Is An Abstract Class?
What Is The Difference Between An Interface And An Abstract Class?
What is the difference Between Hashmap And Hashtable?
How Can You Declare Constant Variables In Java?
Can We Declare A Final Global Variable And Use It Without Initializing It?
What Is Sib (Static Initialization Block)?
When Do SIBs Get Execute?
How Many Times Will SIBs Be Executed In One Execution Cycle?
What Is An Iib?
When Be Will Instance Initialization Block (IIB) Executed?
How Many Times Will IIBs Be Executed In One Execution Cycle?
What Does A Method’s Return Type Signify?
What Is Call By Value And Call By Reference?
What Is A Constructor?
What Are The Two Types Of Constructors?
What Is A Default Constructor?
What Is This() Calling Statement?
What Is Recursion?
Recursion While Constructor Overloading Will Result In Compile-time Or Runtime Error
What Is “this” Keyword?
What Is The Instance Variable Hiding?
What Is The Use Of This Keyword?
What Is Inheritance?
What Are The Different Types Of Inheritance?
What Is Extends Keyword?
Does Java Support Multiple Inheritances?
What Is The Diamond Problem?
Why Doesn’t Java Support Multiple Inheritances?
What Is A Super() Calling Statement?
What Is A “super” Keyword?
What Is The Difference Between Super() Calling And This() Calling Statement?
What Is The Difference Between “super” And “this” Keyword?
What Is Method Overriding?
Can We Override Static Methods?
What Is An Abstract Method?
What Is An Abstract Class?
Can We Instantiate An Abstract Class?
What Is The Rule To Be Followed By The Subclass Of An Abstract Class
Can An Abstract Class Inherit Another Abstract Class
Is Abstract Class 100% Abstract? Explain
What Is An Interface?
What Is The Difference Between An Abstract Class And An Interface?
Does The Abstract Class Have Constructors? If Yes, Why?
Do Interfaces Have Constructors?
Can We Instantiate An Interface?
What Is The Implements Keyword?
Can An Interface Inherit From Another Interface?
What Is Casting?
What Is Primitive Casting?
What Is Auto Widening And Explicit Narrowing?
What Is Derived Or Object Casting?
What Are Auto Upcasting And Explicit Downcasting?
Can We Achieve Object Casting Without Inheritance?
Can We Achieve Downcasting Without Upcasting?
What Is Polymorphism?
Explain Different Types Of Polymorphism.
What Is Abstraction?
What Are The Packages?
Why Packages?
What Are The New Features Released In Java 8?
What Are The Main Benefits Of New Features Introduced In Java 8?
What Is A Lambda Expression In Java 8?
What Are The Three Main Parts Of A Lambda Expression In Java?
What Is The Data Type Of A Lambda Expression?
What Is The Meaning Of Following Lambda Expression?
Why Did Oracle Release A New Version Of Java Like Java 8?
What Are The Advantages Of A Lambda Expression?
What Is A Functional Interface In Java 8?
What Is A Single Abstract Method (Sam) Interface In Java 8?
How Can We Define A Functional Interface In Java 8?
Why Do We Need Functional Interface In Java?
Is It Mandatory To Use @functionalinterface Annotation To Define A Functional Interface In Java 8?
What Are The Differences Between Collection And Stream Api In Java 8?
What Are The Main Uses Of Stream Api In Java 8?
What Are The Differences Between Intermediate And Terminal Operations In Java 8 Streams?
What Is A Spliterator In Java 8?
What Are The Differences Between Iterator And Spliterator In Java 8?
What Is Type Inference In Java 8?
Does Java 7 Support Type Inference?
How Does Internal Iteration Work In Java 8?
What Are The Main Differences Between Internal And External Iterators?
What Are The Main Advantages Of Internal Iterator Over External Iterator In Java 8?
What Are The Applications In Which We Should Use Internal Iteration?
What Is The Main Disadvantage Of Internal Iteration Over External Iteration?
Can We Provide the Implementation Of A Method In A Java Interface?
What Is A Default Method In An Interface?
Why Do We Need Default Method In A Java 8 Interface?
What Is The Purpose Of A Static Method In An Interface In Java 8?
What Are The Core Ideas Behind The Date/time Api Of Java 8?
What Are The Advantages Of New Date And Time Api In Java 8 Over Old Date Api?
What Are The Main Differences Between Legacy Date/time Api In Java And Date/time Api Of Java 8?
How Can We Get Duration Between Two Dates Or Time In Java 8?
What Is The New Method Family Introduced In Java 8 For Processing Of Arrays On Multi-Core Machines?
How Does Java 8 Solve the Diamond Problem Of Multiple Inheritance?
What Are The Differences Between Predicate, Supplier, And Consumer In Java 8?
Is It Possible To Have a Default Method Definition In An Interface Without Marking It With a Default Keyword?
Can We Create A Class That Implements Two Interfaces With Default Methods Of the Same Name And Signature?
How Java 8 Supports Multiple Inheritance?
In Case, We Create A Class That Extends A Base Class And Implements An Interface. If Both Base Class And Interface Have A Default Method With the Same Name And Arguments, Then Which Definition Will Be Picked By Jvm?
If We Create the Same Method And Define It In A Class, In Its Parent Class, And An Interface Implemented By The Class, Then the Definition Will Be Invoked If We Access It Using The Reference Of the Interface And The Object Of the Class?
Can We Access A Static Method Of An Interface By Using Reference Of The Interface?
How Can You Get The Name Of a Parameter In Java By Using Reflection?
What Is Optional In Java 8?
What Are The Uses Of Optional?
Which Method In Optional Provides The Fallback Mechanism In Case Of Null Value?
How Can We Get Current Time By Using Date/time Api Of Java 8?
Is It Possible To Define A Static Method In An Interface?
How Can We Analyze The Dependencies In Java Classes And Packages?
What Are The New Jvm Arguments Introduced By Java 8?
What Are The Popular Annotations Introduced In Java 8?
What Is A String joiner In Java 8?
What Is The Type Of A Lambda Expression In Java 8?
What Is The Target Type Of A Lambda Expression?
What Are The Main Differences Between An Interface With a Default Method And An Abstract Class In Java 8?

Java Interview Questions On Strings

What Is The Difference Between StringBuffer & StringBuilder?
What Is Difference B/w String S=new String(),string S=””;
Is String A Data Type In Java?
Why Is StringBuffer Called Mutable?
What Are The Different Access Levels In Java? Explain
What Is Singleton Class?
What Is Encapsulation?
Which Is The Uppermost Class For All The Classes In Java?
Explain “toString()” Of Object Class
Explain “hashcode()” Of Object Class
Explain “equals()” Of Object Class
Can A Subclass Override All These Above Methods?
What Is The Final Method In Java?
What Is The Final Class In Java?
What Is The Use Of Finalize() Method In Java?
What Is The Use Of The Clone() Method?
What Is A Marker Interface? Explain And Mention At Least Two Available Marker Interface
Strings Are Immutable In Java. Justify
Can We Have Inherited The String Class? Justify
Explain The Behavior Of Tostring(),hashcode() And Equals() Method Of String Class
What Is A String Constant Pool And Non-constant Pool?
What Are Arrays?
What Is A Primitive Array?
What Is A Derived Array?
What Are Boxing And Unboxing?
What Are The Wrapper Classes?
What Is A Collection Api/framework?
Explain the List Type Of Collection.
Explain the Set Type Of Collection.
Explain The Queue Type Of Collection.
List Out The Differences Between List, Set, And Queue Types Of Collections.
What Are The Exceptions?
How To Handle An Exception?
What Has Checked Exceptions?
What Are Unchecked Exceptions?
Different Ways Of Handling Checked Exceptions?
What Is The Difference Between Final, Finalize(), And Finally In Java
How To Write The Data Into A Text File?
How To Read Data From A Text File?
What Is The Use Of The Scanner Class In Java?
How To Read The String From The Console?

Java Interview Questions Collections

What Is Collection?
What Is List?
What Is The Difference Between ArrayList And LinkedList?
What Is The Difference Between List, Set, Map
What Is the Difference Between Vector And Arraylist?
What Is The Difference Between Hashmap And Hashtable
What Is The Difference Between Collection And Array?
What Is the Difference between HashSet And Linkedhashset
What Is Iterator In Java?
What Is the Difference between Listiterator And Iterator
What Is The Default Capacity Of Arraylist And Hashtable?
What Is The Difference Between Constructor And Method
What Is The Difference Between This And Super In Java?
How To Sort Employee Class Using Comparator?
What Is Super Most Class In Java, And Explain All Methods Of The Superclass?
How Do You Differentiate A HashSet Class And A Treeset Class?
What Is A List? What Is The Difference Between An ArrayList And A LinkedList?
What Is Collection And A Collections Framework?
What Is The Difference Between ArrayList And Vector?
What’s The Difference Between Stack And Queue?
What Is An Array
What is the difference Between Array And Arraylist?
How To Sort The Collections?
What Is Treeset?
In Which Scenarios, ArrayList And Linkedlist Will Be Used?
What Happens If You Add the Same Key In The Hashmap?
Can We Add a Null Key To The Hashmap?
Hashmap Put() Operations Uses Which Datastrcture When The Hashcode Is Same?

Java Interview Questions On Exception Handling

How to handle Exception in java explain?
What are try, catch, and finally?
What is throw and throws?
Will all the Try blocks in Java ends with Catch Blocks?
What is the Final Keyword in Java?
Which types of exceptions are caught at compile time?
What is an Exception?
When is the throw keyword used?
Which types of exceptions are caught at compile time?
What is an Exception? Types of Exception?
Explain Exception Handling methods.
What are the types of exceptions in Java?
Mention the different methods to handle exceptions
Provide the benefits of exception handling
Provide the exception handling keywords available in Java
What is Locale in Java?
How will you use a specific Locale in Java?
What is serialization?
What is the purpose of serialization?
What is Deserialization?
What are Serialization and Deserialization conceptually?
Why do we mark a data member transient?
Is it allowed to mark a method as transient?
How does marking a field as transient makes it possible to serialize an object?
What is an Externalizable interface in Java?
What is the difference between a Serializable and Externalizable interface?
What is Reflection in Java?
What are the uses of Reflection in Java?
How can we access the private method of a class from outside the class?
How can we create an Object dynamically at Runtime in Java?
What is Garbage Collection in Java?
Why Java provides Garbage Collector?
What is the purpose of gc() in Java?
How does Garbage Collection work in Java?
When does an object become eligible for Garbage Collection in Java?
Why do we use finalize() method in Java?
What are the different types of References in Java?
How can we reference an unreferenced object again?
What is the purpose of the Runtime class?
How can we invoke an external process in Java?
What are the uses of the Runtime class?
What is a Nested class?
How many types of Nested classes are in Java?
Why do we use Nested Classes?
What is the difference between Nested and Inner classes in Java?
What is a Nested interface?
How can we access the non-final local variable inside a Local Inner class?
Can an Interface be defined in a Class?
Do we have to mark a Nested Interface as public static explicitly?
Why do we use the Static Nested interface in Java?
What are Wrapper classes in Java?
What is the purpose of the native method in Java?
What is a System class?
What is System, out, and println in System.out.println method calls?
What is the other name of Shallow Copy in Java?
What is the difference between Shallow Copy and Deep Copy in Java?
What is a Singleton class?
What is the difference between the Singleton class and the Static class?

Java Interview Questions On Multithreading

Explain multi-threading and the ways of implementing multi-threading in Java.
What do you mean by BlockingQueue in Java Collections Framework?
Name the different states of a thread.
What are the two ways of implementing multi-threading in Java?
How will you call the wait() method? Would you use if block or loop, and why?
How do you take thread dump in Java?
What is the difference between sleep and wait in Java?
Is ++ operator thread-safe in Java?
What is the difference between poll() and remove() methods?
What is Multitasking? How to achieve multitasking?
What is Thread?
What is Multithreading?
What is the difference between Multithreading and Multiprocessing?
Which thread will execute first?
How to get the current thread?
What is thread
What is synchronisation
Which methods are there in the thread class?
Can we have two start() methods in thread execution?
Which will manage the lifecycle of the thread?
What is the default priority of the thread?
Describe Thread in Java
Describe wait() method
Explain notify () and notify all () methods
Provide the list of thread methods to stop a thread in Java
Describe the thread life cycle of Java
Define Serialization
What is a thread?
Pre-increment/decrement and post-increment/decrement
What is threading?
How does multithreading achieve?
How to initiate a thread in java?
What do you mean by thread-safe?
What are Threads?
What is the use of sleep() method in Threads?
Explain wait(), notify() and notifyAll() methods of the Object class.
Can we Override wait(), notify(), and notifyAll() methods of the Object class in the sub-classes?
What kind of process is the Garbage collector thread?
How can you ensure that N threads can access N resources without deadlock?
How can we share an object between multiple threads?
What is the difference between a process and a thread in Java?
Can you catch an exception thrown by another thread in Java?
How can you determine if your program has a deadlock?
Is ++ operation thread-safe in Java?
What is a thread-local variable in Java?
How will you take thread dump in Java?
How to achieve lock?

Java Interview Questions On Inheritance

Does java support multiple inheritances?
Can we develop final methods in an interface?
Can we develop a final abstract class?
Can we develop a static method in an abstract class?
Can we declare a variable in the interface without initializing it?
What is the difference between JDK and JRE?
What is Java Virtual Machine (JVM)?
What are the different types of memory areas allocated by JVM?
What is a JIT compiler?
How is the Java platform different from other platforms?
Why did people say Java is a ‘write once and run anywhere’ language?
How does ClassLoader work in Java?
Do you think ‘main’ used for the main method is a keyword in Java?
Can we write the main method as public void static instead of the public static void?
In Java, if we do not specify any value for local variables, what will be the default value of the local variables?
Let’s say we run a java class without passing any arguments. What will be the value of the String array of arguments in the Main method?
What is the difference between byte and char data types in Java?
In Java, why do we use a static variable?
Why it is not a good practice to create static variables in Java?
What is the purpose of the static method in Java?
Why do we mark the main method as static in Java?
In what scenario do we use a static block?
Is it possible to execute a program without defining a main() method?
What happens when the static modifier is not mentioned in the signature of the main method?
What is the difference between static and instance methods in Java?
How can you change the value of a final variable in Java?
Can a class be marked final in Java?
How can we create a final method in Java?
How can we prohibit inheritance in Java?
Why is the Integer class in the final in Java?
What is a blank final variable in Java?
How can we initialize a blank final variable?
Is it allowed to declare the main method as final?
What is the purpose of the package in Java?
What is java.lang package?
Which is the most important class in Java?
Is it mandatory to import java.lang package every time?
Can you import the same package or class twice in your class?
What is a static import in Java?
What is the difference between import static com.test.Fooclass and import com.test.Fooclass?

Java Interview Questions Advanced

What’s the exception?
Are the exceptions defined in JavaScript packages? Or are there any definitions for all classes?
What are the types of exceptions?
What is the difference between an error and an exception?
What is the keyword in exceptional handling?
What is the keyword?
Throwing in Java
Can the standard block be lifted?
What is banned?
NoClassDefFoundError versus ClassNotFoundException?
Can we try or not try to stop it?
Can you handle a catch in an exception to an exception?
What is Java Bean?
Define JAVA
Why do we say Java is dynamic?
List out the different access specifiers available for Java classes
Define Loops in Java. Provide the different types of loops in Java
List out the constructors in Java
What is the difference between List and a Set?
Can we create an object for the abstract class? If not, why?
Whether we can declare a class as static?
Polymorphism w.r.t variables and methods? Or overriding and overloading?
In what way we can sort the elements(default and custom sort) present in the array and any of the collection objects?
How to generate random numbers in java? And also generate random numbers of format ‘A23BC’?
Is it possible to call protected data members of one package in another? Similarly, all other access modifiers and their data members scope from other packages.

Java Interview Questions For Freshers

Explain Method Overriding
Define Interface in Java
List out the advantages of Java packages
Do you know whether the constructor returns any value in Java?
Is it possible to make a constructor final?
Is it possible to overload the constructors?
Explain static block
Explain the keyword “this” in Java.
Mention the class, which is the superclass for the entire class.
Define Aggregation
Explain the keyword “Super” in Java
List out the vital advantages of the keyword “Super.”
Is it possible to use both “this()” and “super()” in a constructor?
Will you be able to overload the main() method?
Explain final variable
Is it possible for you to declare a constructor as final?
Mention the difference between the abstract and the final method
Explain the purpose of encapsulation
Explain Polymorphism
Define Java Collections
What are the operations of collections?
List out the interfaces available in Java collections
List out the Classes available in Java collections
List out the maps available in Java collections
Can you give an example of pointers?
Provide the features of the Hashtable method
Explain HashSet
Explain TreeSet
How do you decide which type of Inner Class – Static or Non-Static to use in Java?
What are the different types of Classloaders in Java?
What are the situations in which you choose HashSet or TreeSet?
What is the use of method references in Java?
Do you think Java Enums are more powerful than integer constants?
Why do we use static initializers in Java?
Your client is complaining that your code is throwing NoClassDefFoundError or NoSuchMethodError, even though you can compile your code without error and the method exists in your code. What could be the reason behind this?
Using a regular expression, how can you check if a String is a number?
What is the difference between the expressions String s = “Temporary” and String s = new String(“Temporary “)? Which one is better and more efficient?
In Java, can two equal objects have different hash codes?
How can we print an Array in Java?
Is it ok to use random numbers to implement the hashcode() method in Java?
Which is better between the two types of dependency injections, constructor and setter dependency injections?
What is the difference between DOM and SAX parser in Java?
Between Enumeration and Iterator, which one has better performance in Java?
What is the difference between pass-by-reference and pass-by-value?
What are the different ways to sort a collection in Java?
Why doesn’t the Collection interface extend Cloneable and Serializable interfaces?

Java Interview Questions For Experienced

Is it possible to declare a class as Abstract without using any abstract method?
Any five differences between an Abstract Class and Interface in Java?
Define Serialization. When should we make use of serialization?
Is it true that a java program never goes out of memory because of the garbage collection feature?
How can you define Object Cloning in Java?
Is throw and throws keywords can be used interchangeably? If not, what is the difference between the two?
Are you connecting to a database in Java?
Functions of JVM and JRE?
What is the default size of the loaded factor in hacking based on the collection?
What is a collection?
What Exception Classes are the Basic Classes?
Two differences in the state between a class and one square
How are they destroyed in Java?
Define JSON.
Name the most important aspect of Java
What is an anonymous class?
What is a JVM?
Can a Dead End Start Again?
Sort of ancient data types?
What researchers are in Java?
Explain garbage in Java.
What’s the difference between the stack and the queue?
What is a standard method?
Explain the keyword of Java.
The use of Java’s last words?
What is the subject class?
What are the packages in Java?
What’s the difference between importing java.util.Date and java.util? *?
What is the standard import?
Garbage collection in Java?
Decision-Making in Java
How often do you call the trash cushion for the last time () method for an object?
How can garbage collection be enforced?
What is a class?
What is the difference between heap and stack?
What is the difference between an instance variable and a local variable?
What is Constructor? Types of Constructors?
What is the difference between Break and Continue?
To exit the system from the current execution, what command is used in java?
Addition features in Java 8?
What is the difference between for and for each loop in java and its use of it?
Can we have multiple public classes within a class?
What is inheritance? Types of inheritance? Do multiple inheritances allow in java? If not, why?
What is polymorphism? How can we achieve it?
What is the difference between method overloading and method overriding?
Can we achieve method overloading when two methods have only differences in return type?
Method overloading and overriding examples in the Selenium project?
What is encapsulation?
What are IS-A and HAS-A relations in java With examples?
What is the final and super keyword? What difference between them?
Explain runtime polymorphism and compile-time with examples.
Can the final/Static method be overloaded?
Can final/Static methods be overridden?
Can we overload the main method?
Can we execute a class without a main method?
What is a Package?
What is an Abstract Class? Write an example code.
What is an Interface? What is the difference from the Abstract class?
Can we use private and protect access modified inside an Interface?
Can multiple inheritances support the Interface?
Examples of Abstract and Interface used in the selenium project?
What is an Exception, and what is its base class of it?
What is Final, Finally, Finalize?
What is done in finally block?
What is garbage collection in java? How it is done?
What is the difference between Throws and throws?
What is Java Reflection, Singleton?

Java Tricky Interview Questions

Define Constructor and Constructor Overloading in Java.
What are the differences between Enumeration and Iterator?
Why is a break used in Switch Statement’s each case?
How can we execute any code even before the main method?
What’s the benefit of using inheritance as a key?
Define Expressions.
What will be the result of relational operators?
Which operators are used for masking the data in the encryption and decryption process?
Which is maintained to manage the life cycle of local variables?
In how many ways can the object be created?
The object which has no reference is called?
In Heap memory which variables are created?
In java, how are arrays created?
Which operator is not used in java?
Define Runtime Polymorphism.
When does a null pointer exception occur?
When Out of a memory error occurs?
Can exceptions occur in the catch block?
What will happen if we use the throws keyword in the body?
Which exceptions are used to represent the business/environmental failure?
In Java, Why multiple inheritances are not supported?
Which feature allows the JVM to run more than one thread in java?
What is Java?
What is Interface?
What is the difference between Interface and Abstraction?
What is Serialization?
What is DeSerialization?
When an Out of a stack error occurs?
Where are all string literals managed?
Which condition will result in an Illegal state exception?
What is the default priority of gc()?
Which interface will result in sorted order?
What is Comparator?
What is a workspace?
Which will interact with the hard disk?
What are Access specifiers?
Why can we not apply access specifiers to packages, initializers, and local variables?
When we can use final class?
Abstract class cannot be instantiated. Why?
Abstract method cannot have body, why?
Define class in Java.
What is the difference between fixed and dynamic loads?
What is Multiple Mitigation?
When was Java created?
What stand is for JDK, JRR and JVM?
Need Java Use Pointers?
What is a singleton class?
Explain List
Explain Set
Explain Map
Why are strings immutable?
What is an exception? And its types?
What is a checked and unchecked exception?
What is a comparable and comparator?
Can we break a singleton object with the clone method? How to avoid that?
Can we break singleton objects with serialization? How to avoid that?
Can we break a singleton object with a reflection API on how to avoid that?
Can we break a singleton object with multiple classloaders? On how to avoid that?
What is the best way to create a singleton object in Java?
What is double-checking lock-in Singleton in Java?
Difference between static and Singleton object in Java
Whenever going to an interview, please learn Singleton’s object above cases.

Java Interview Questions For Selenium

Why Collection, and where you used the Collection of Selenium?
What are keywords, data type, constant and variable
What are the fundamental data type in c
What is the conditional statement?
What is the unconditional statement?
What is if—else statement
What are switch case statements?
What is a conditional operator?
What is the iterative statement?
What is sorting
What is searching
What is function
Explain the type of user-defined function
What is a recursive function?
What is structure
What is the difference between structure and union?
What is a pre-processor directive?
What is micro in c
What is file
What is a file pointer
What is a data structure?
What is stack
What is queue
What is a link list
What is a binary tree?
What is spanning tree
What is polymorphism
What is abstraction
What is inheritance
What is a static keyword
What is a pure virtual function?
What is Java
What final in java
What is a super keyword in java?
What is the difference between abstract and interface?
What is an applet program?
What is swing
What are the benefits of using an unordered array over an ordered array?
Between HashSet and TreeSet collections in Java, which one is better?
When does JVM call the finalize() method?
When would you use the Serial garbage collector or Throughput Garbage collector in Java?
In Java, if you set an object reference to null, will the Garbage Collector immediately free the memory held by that object?
How can you make an Object eligible for Garbage collection in Java?
When do you use Exceptions or Errors in Java? What is the difference between these two?
What is the advantage of PreparedStatement over Statement class in Java?
In Java, what is the difference between throw and throws keywords?
What happens to the Exception object after the exception handling is done?
How do you find which client machine is sending requests to your servlet in Java?
What is the difference between a Cookie and a Session object in Java?
Which protocol do Browser and Servlet use to communicate with each other?
What is HTTP Tunneling?
Why do we use JSP instead of Servlet in Java?
Is an empty ‘.java’ file name a valid source file name in Java?
How do you implement Servlet Chaining in Java?
Can you instantiate this class?
Why does Java not support operator overloading?
Why String class is Immutable or Final in Java?
What is the difference between the sendRedirect and forward methods?
How do you fix your Serializable class if it contains a un-serializable member?
What is the use of run time polymorphism in Java?
What are the rules of method overloading and method overriding in Java?
What is the difference between a class and an object in Java?
Can we create an abstract class that extends another abstract class?
Why do you use Upcasting or Downcasting in Java?
What is the reason for organizing classes and interfaces in a package in Java?
What is information hiding in Java?
Why does Java provide a default constructor?
What is the difference between super and this keyword in Java?
What is the advantage of using Unicode characters in Java?
Can you override an overloaded method in Java?
How can we change the heap size of a JVM?
Why should you define a default constructor in Java?
How will you make an Object Immutable in Java?
How can you prevent SQL Injection in Java Code?
Which two methods should be always implemented by HashMap key Object?
Why should an Object used as a Key in HashMap be Immutable?

Java Interview Questions For Testers

What kind of variables can a class consist of?
What is Singleton’s class?
List the three steps for creating an Object for a class.
When is a byte datatype used?
What do you mean by Access Modifier?
When can be the parseInt() method used?
When is a super keyword used?
Why is Runnable Interface used in Java?
What’s the purpose of using Break in each case of Switch Statement?
How can we execute any code even before the main method?
Can we have two methods in a class with the same name?
How can we make a copy of a Java object?
Can we use a class’s default constructor even if an explicit constructor is defined?
Can we override a method by using the same method name and arguments but different return types?
What is an applet?
What is a Comparable Interface?
Why IS the Java application platform independent?
What are the actions present in the JVM?
What is the current version of JDK?
Which data structure set is used?
Is wrapper classes override hashcode and equals method?
Does java 8 support functional programming?
What is the default method in the java 8 interface?
What is the difference between StringBuffer and StringBuilder?
What exceptional handling
What is JDBC
What is the JDBC driver
What are the steps involved in database connectivity
What is servlet
What is the life cycle of a servlet
Write a servlet program
What is Jsp
What is the difference between while and do-while
From which method the execution of java programs begins?
Which name will be checked by the compiler for the execution of the program?
Which name will be checked by the JVM after compiling the program?
Can we have the filename and class name as same?
Why are we injecting interface references in the spring framework? Why not direct implementation?
Tell me about Hash Map implementation
Difference between Linked List and Array List
How to make a map a synchronized map
What is the difference between Collections.synchronizedMap(m) and concurrent hash map
Difference between forEach and iterator
Can we instantiate the interface? If not, then why?
What is the difference between classNotFoundException and NoClassDefError in which situation will we face this?
What is serializable? If my business object does not implement serializable, is there any problem?

Conclusion:

Preparing for these questions lets you demonstrate your proficiency and problem-solving skills to potential employers. By familiarizing yourself with an extensive array of topics, ranging from fundamentals to advanced Java concepts, you can confidently navigate the interview process. It is important to remember that practice and hands-on experience are the keys to success. So keep refining your Java programming skills and stay updated with the language’s latest developments to ace your Java interview.

We greatly appreciate and encourage feedback on the comments on Java interview questions, as it fosters a collaborative learning environment. By sharing your thoughts, experiences, and knowledge, you contribute to the ongoing improvement and expansion of the content available on this platform. Your feedback not only supports fellow developers in their quest to master Java development but also helps us refine and optimize the resources we provide. So, don’t hesitate to leave a comment or suggestion—your input is valuable in creating a comprehensive and engaging learning experience for all.

Core Java Interview Questions: Java is one of the most popular programming languages developers and testers use worldwide. Core Java interview questions are crucial in evaluating the skills and proficiency of candidates in Java programming.

Whether you are a fresher or an experienced developer, it is essential to have a thorough understanding of Core Java, including its concepts, syntax, and applications. Core Java Interview Questions for Freshers & Experienced are designed to assess a candidate’s knowledge of Core Java concepts, such as OOPs, methods, classes, languages, control statements, inheritance, and exception handling, among others.

In this context, this article provides an extensive list of common Core Java Interview Questions for Freshers and Experienced candidates, which can help them prepare for job interviews and improve their overall knowledge in Java programming.

Core Java Interview Questions For Freshers

How many methods are there in object class?
Ans: 11 methods, below is the list

protected Object clone() throws CloneNotSupportedException – Creates and returns a copy of this object.
Public boolean equals(Object obj) – Indicates whether some other object is “equal to” this one.
Protected void finalize() throws Throwable – Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
public final Class getClass() – Returns the runtime class of an object.
public int hashCode() – Returns a hash code value for the object.
Public final void notify() – Wakes up a single thread that is waiting on this object’s monitor.
Public final void notifyAll() – Wakes up all threads that are waiting on this object’s monitor.
Public String toString() – Returns a string representation of the object.
Public final void wait() – Causes current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.
public final void wait(long timeout)
public final void wait(long timeout, int Nanos)

Hashcode method return type?
Ans: integer

what is the finalize method and when it use?
Ans: Garbage collection, it executed before garbage collector runs.

What is equals methods?
Ans: it is used in 2 places, one is a string class, and another is an object class. In string class, it is overridden. In object class, it checks the addresses, and in string class, it checks the contents.

What is the difference between equal and hashcode?
Ans: hashcode can be the same; it is used internally to find out the uniqueness of an object.
Kiran — 89
Naikr — 89
suppose k=23,i=4
Then both Kiran and Naikr have the same hashcode, but both are not the same. But if equals return same, then there must be the same hashcode.

is it compulsory to write body in a method?
Ans: no, ex-abstract class, interface

why do we need to learn encapsulation?
Ans: binding data variables and method in a single unit is called encapsulation. We are using encapsulation to protect our class from others so that others can not extract our class. Her variables should be private and method some time public so that our requirement solved properly.

Difference between encapsulation and abstraction?
Ans: in abstraction, we expose only the required things. But in encapsulation, we are binding the data properly.

What is polymorphism?
Ans: behaving differently at different time by the same entity. It can achieve in 2 ways. Overloading and overriding. in overloading this happens and in overriding this happen.

Why are you using overriding?
Ans: To change the implementation of the parent class.

Why we use interface?
Ans: if we want 100% abstraction then we should go with an interface. To maintain standards.

Core Java Interview Questions Experienced

Do you need to implement all methods of interface?
Ans: if you don’t want to implement all methods, then you have to make that class as abstract.

What is the use of an abstract class?
Ans: if you want to implement or expose some methods and don’t want to implement some methods then go for abstract class

List l=new ArrayList(); and ArrayList al=new ArrayList(); which is good and why ?
Ans: List l=new ArrayList() is good.

what is the difference between final and static?
Ans: in final, the value can not be changed, but in static, you can change the value.

What is difference between JDK,JRE and JVM?
Ans:
JVM: JVM is an acronym for Java Virtual Machine, it is an abstract machine which provides the runtime environment in which Java bytecode can be executed. It is a specification. JVMs are available for many hardware and software platforms (so JVM is platform dependent).
JRE: JRE stands for Java Runtime Environment. It is the implementation of JVM.
JDK: JDK is an acronym for Java Development Kit. It physically exists. It contains JRE + development tools.

How many types of memory areas are allocated by JVM?
Ans: Many types:

Class(Method) Area
Heap
Stack
Program Counter Register
Native Method Stack

What is JIT compiler?
Ans: Just-In-Time(JIT) compiler: It is used to improve performance. JIT compiles parts of the bytecode that have similar functionality at the same time, and hence reduces the amount of time needed for compilation. Here the term “compiler” refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.

What is a platform?
Ans: A platform is the hardware or software environment in which a program runs. There are two types of platforms software-based and hardware-based. Java provides the software-based platform.

What is the main difference between the Java platform and other platforms?
Ans: The Java platform differs from most other platforms in the sense that it’s a software-based platform that runs on top of other hardware-based platforms. It has two components:

Runtime Environment
API(Application Programming Interface)

Core Java Interview Questions 5 Years Experience

What gives Java its ‘write once and run anywhere’ nature?
Ans: The bytecode. Java is compiled to be a bytecode which is the intermediate language between source code and machine code. This bytecode is not platform specific and hence can be fed to any platform.

What is classloader?
Ans: The classloader is a subsystem of JVM that is used to load classes and interfaces. There are many types of classloaders, e.g. Bootstrap classloader, Extension classloader, System classloader, Plugin classloader etc.

Is Empty .java file name a valid source file name?
Ans: Yes, save your java file by .java only, compile it by javac .java and run by java your class name. Let’s take a simple example:

//save by .java only
class A{
public static void main(String args[]){
System.out.println("Hello java");
}
}
//compile by javac .java
//run by java A
compile it by javac .java

Ans: run it by java A

If I don’t provide any arguments on the command line, then the String array of Main method will be empty or null?
Ans: It is empty. But not null.

What if I write static public void instead of the public static void?
Ans: Program compiles and runs properly.

What is the default value of the local variables?
Ans: The local variables are not initialized to any default value, neither primitives nor object references.

What is the difference between an object-oriented programming language and object-based programming language?
Ans: Object-based programming languages follow all the features of OOPs except Inheritance. Examples of object-based programming languages are JavaScript, VBScript etc.

What will be the initial value of an object reference which is defined as an instance variable?
Ans: The object references are all initialized to null in Java.

What is a constructor?
Ans: Constructor is just like a method that is used to initialize the state of an object. It is invoked at the time of object creation.

What is the purpose of a default constructor?
Ans: The default constructor provides the default values for the objects. The java compiler creates a default constructor only if there is no constructor in the class.

Does constructor return any value?
Ans: yes, that is a current instance (You cannot use return type yet it returns a value).

Is constructor inherited?
Ans: No, the constructor is not inherited.

Can you make a constructor final?
Ans: No, constructor can’t be final.

Core Java Interview Questions For 10 Years Experienced

What is a static variable?
Ans: static variable is used to refer the common property of all objects (that is not unique for each object), e.g. company name of employees, college name of students etc. static variable gets memory only once in a class area at the time of class loading.

What is the static method?
Ans: A static method belongs to the class rather than an object of a class. A static method can be invoked without the need for creating an instance of a class. the static method can access static data member and can change the value of it.

Why is the main method static?
Ans: because the object is not required to call the static method if It were a non-static method, JVM creates the object first then call the main() method that will lead to the problem of extra memory allocation.

What is a static block?
Ans: Is used to initialize the static data member. It is executed before the main method at the time of classloading.

Can we execute a program without main() method?
Ans: Yes, one of the ways is a static block.

What if the static modifier is removed from the signature of the main method?
Ans: Program compiles. But at runtime throws an error “NoSuchMethodError”.

What is the difference between static (class) method and instance method?
Ans: static or class method instance method

Static Method	Instance Method
A method, i.e. declared as static is known as a static method.	A method, i.e. not declared as static, is known as an instance method.
The object is not required to call the static method.	The object is required to call instance methods.
Non-static (instance) members cannot be accessed in a static context (static method, static block, and static nested class) directly.	Static and non-static variables can be accessed in instance methods.
For example: public static int cube(int n){ return nnn;}	For example: public void msg(){…}.

What is this in java?
Ans: It is a keyword that that refers to the current object.

What is Inheritance?
Ans: Inheritance is a mechanism by which one object acquires all the properties and behaviour of another object in another class. It represents the IS-A relationship. It is used for Code Reusability and Method Overriding.

Which class is the superclass of every class?
Ans: Object class.

Why are multiple inheritances not supported in java?
Ans: To reduce the complexity and simplify the language, multiple inheritances are not supported in java in case of class.

What is composition?
Ans: Holding the reference of the other class within some other class is known as composition.

What is the difference between aggregation and composition?
Ans: Aggregation represents a weak relationship, whereas composition represents a strong relationship. For example, the bike has an indicator (aggregation), but the bike has an engine (composition).

Why does Java not support pointers?
Ans: Pointer is a variable that refers to the memory address. They are not used in Java because they are unsafe(unsecured) and complex to understand.

What is super in java?
Ans: It is a keyword that refers to the immediate parent class object.

Can you use this() and super() both in a constructor?
Ans: No. Because super() or this() must be the first statement.

What is object cloning?
Ans: The object cloning is used to create the exact copy of an object.

What is method overloading?
Ans: If a class have multiple methods by the same name but different parameters, it is known as Method Overloading. It increases the readability of the program.

Why is method overloading not possible by changing the return type in java?
Ans: Because of ambiguity.

Core Java Interview Questions For 3 Years Experience

Can we overload the main() method?
Ans: Yes, You can have many main() methods in a class by overloading the main method.

What is method overriding:
Ans: If a subclass provides a specific implementation of a method that is already provided by its parent class, it is known as Method Overriding. It is used for runtime polymorphism and to provide the specific implementation of the method.

Can we override the static method?
Ans: No, you can’t override the static method because they are the part of class not object.

Why can we not override static method?
Ans: It is because the static method is the part of a class and it is bound with class whereas instance method is bound with an object and static gets memory in the class area, and instance gets memory in a heap.

Can we override the overloaded method?
Ans: Yes.

Difference between method Overloading and Overriding.
Ans:

Method Overloading	Method Overriding
Method overloading increases the readability of the program.	Method overriding provides the specific implementation of the method that is already provided by its superclass.
Method overloading occurs within the class.	Method overriding occurs in two classes that have an IS-A relationship.
In this case, a parameter must be different.	In this case, a parameter must be the same.

Core Java Interview Questions For Selenium

What is the final variable?
Ans: If you make any variable as final, you cannot change the value of a final variable(It will be constant).

What is the final method?
Ans: Final methods can’t be overridden.

What is the final class?
Ans: Final class can’t be inherited.

What is the final blank variable?
Ans: A final variable, not initialized at the time of declaration, is known as a final blank variable.

Can we initialize the final blank variable?
Ans: Yes, only in the constructor if it is non-static. If it is static blank final variable, it can be initialized only in the static block.

Can you declare the main method as final?
Ans: Yes, such as public static final void main(String[] args){}.

What is Runtime Polymorphism?
Ans: Runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time.
In this process, an overridden method is called through the reference variable of a superclass. The determination of the method to be called is based on the object being referred to by the reference variable.

Can you achieve Runtime Polymorphism by data members?
Ans: No.

What is the difference between static binding and dynamic binding?
Ans: In case of a static binding type of object is determined at compile time whereas in a dynamic binding type of object is determined at runtime.

What is abstraction?
Ans: Abstraction is a process of hiding the implementation details and showing only functionality to the user.
Abstraction lets you focus on what the object does instead of how it does it.

What is the difference between abstraction and encapsulation?
Ans: Abstraction hides the implementation details, whereas encapsulation wraps code and data into a single unit.

What is an abstract class?
Ans: A class that is declared as abstract is known as an abstract class. It needs to be extended, and its method implemented. It cannot be instantiated.

Can there be any abstract method without an abstract class?
Ans: No, if there is an abstract method in a class, that class must be abstract.

Can you use abstract and final both with a method?
Ans: No, because the abstract method needs to be overridden, whereas you can’t override a final method.

Is it possible to instantiate the abstract class?
Ans: No, the abstract class can never be instantiated.

What is an interface?
Ans: Interface is a blueprint for a class that has static constants and abstract methods. It can be used to achieve full abstraction and multiple inheritances.

Can you declare an interface method static?
Ans: No, because methods of an interface are abstract by default, and static and abstract keywords can’t be used together.

Can an Interface be final?
Ans: No, because another class provides its implementation.

What is marker interface?
Ans: An interface that has no data member and method is known as a marker interface. For example, Serializable, Cloneable etc.

What is the difference between abstract class and interface?
Ans: Abstract class Interface

An abstract class can have a method body (non-abstract methods). The interface has only abstract methods.
An abstract class can have instance variables. An interface cannot have instance variables.
An abstract class can have a constructor. An interface cannot have a constructor.
An abstract class can have static methods. An interface cannot have static methods.
You can extend one abstract class. You can implement multiple interfaces.

Can we define private and protected modifiers for variables in interfaces?
Ans: No, they are implicitly public.

When can an object reference be cast to an interface reference?
Ans: An object reference can be cast to an interface reference when the object implements the referenced interface.

What is a package?
Ans: A package is a group of similar type of classes interfaces and sub-packages. It provides access protection and removes naming collision.

Do I need to import java?lang package any time? Why?
Ans: No. It is by default loaded internally by the JVM.

Can I import the same package/class twice? Will the JVM load the package twice at runtime?
Ans: One can import the same package or the same class multiple times. Neither compiler nor JVM complains about it. But the JVM will internally load the class only once no matter how many times you import the same class.

What is a static import?
Ans: By static import, we can access the static members of a class directly, there is no to qualify it with the class name.

What is Exception Handling?
Ans: Exception Handling is a mechanism to handle runtime errors. It is mainly used to handle checked exceptions.

What is the difference between Checked Exception and Unchecked Exception?
Ans:

Checked Exception	Unchecked Exception
The classes that extend Throwable class except RuntimeException and Error are known as checked exceptions e.g.IOException, SQLException etc. Checked exceptions are checked at compile-time.	The classes that extend RuntimeException are known as unchecked exceptions, e.g. ArithmeticException, NullPointerException etc. Unchecked exceptions are not checked at compile-time.

What is the base class for Error and Exception?
Ans: Throwable.

Is it necessary that a catch block must follow each try block?
Ans: It is not necessary that a catch block must follow each try block. It should be followed by either a catch block OR a finally block. And whatever exceptions are likely to be thrown should be declared in the throws clause of the method.

What is finally block?
Ans: finally block is a block that is always executed.

Can finally block be used without a catch?
Ans: Yes, by try block. finally must be followed by either try or catch.

Is there any case when finally will not be executed?
Ans: finally will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort).

What is the difference between throw and throws?
Ans:

Throw Keyword	Throws Keyword
throw is used to throw an exception explicitly.	Throws are used to declare an exception.
Checked exceptions cannot be propagated with throw only.	A checked exception can be propagated with throws.
An instance follows the throw.	Throws are followed by class.
the throw is used within the method.	Throws are used with the method signature.
You cannot throw multiple exceptions	You can declare multiple exceptions, e.g. public void method()throws IOException, SQLException.

Can an exception be rethrown?
Ans: Yes.

Can subclass overriding method declare an exception if the parent class method doesn’t throw an exception?
Ans: Yes, but only unchecked exception not checked.

What is exception propagation?
Ans: Forwarding the exception object to the invoking method is known as exception propagation.

What is the meaning of immutable in terms of String?
Ans: The simple meaning of immutable is unmodifiable or unchangeable. Once the string object has been created, its value can’t be changed.

Why are string objects immutable in java?
Ans: Because Java uses the concept of a string literal. Suppose there are 5 reference variables, all refer by one object “Sachin”.If one reference variable changes the value of the object, it will be affected by all the reference variables. That is why string objects are immutable in java.

How many ways can we create the string object?
Ans: There are two ways to create the string object, by a string literal and by new keyword.

Core Java Coding Interview Questions

How many objects will be created in the following code?
Ans:
String s1=”Welcome”;
String s2=”Welcome”;
String s3=”Welcome”;
Only one object.

Why java uses the concept of a string literal?
Ans: To make Java more memory efficient (because no new objects are created if it exists already in constant string pool).

How many objects will be created in the following code?
Ans: String s = new String(“Welcome”);
Two objects, one in constant string pool and other in non-pool(heap).

What is the basic difference between string and StringBuffer object?
Ans: String is an immutable object. StringBuffer is a mutable object.

What is the difference between StringBuffer and StringBuilder?
Ans: StringBuffer is synchronized whereas StringBuilder is not synchronized.

How can we create an immutable class in java?
Ans: We can create an immutable class as the String class by defining a final class and

What is the purpose of the toString() method in java?
Ans: The toString() method returns the string representation of an object. If you print any object, java compiler internally invokes the toString() method on the object. So overriding the toString() method, returns the desired output, it can be the state of an object etc. depends on your implementation.

What is a nested class?
Ans: A class which is declared inside another class is known as a nested class. There are 4 types of nested class member inner class, local inner class, anonymous inner class, and static nested class.

Is there any difference between nested classes and inner classes?
Ans: Yes, inner classes are non-static nested classes, i.e. inner classes, are the part of nested classes.

Can we access the non-final local variable, inside the local inner class?
Ans: No, the local variable must be constant if you want to access it in a local inner class.

What is a nested interface?
Ans: Any interface, i.e. declared inside the interface or class, is known as a nested interface. It is static by default.

Can a class have an interface?
Ans: Yes, it is known as the nested interface.

Can an Interface have a class?
Ans: Yes, they are static implicitly.

What is Garbage Collection?
Ans: Garbage collection is a process of reclaiming the unused runtime objects. It is performed for memory management.

What is GC()?
Ans: GC() is a daemon thread.GC() method is defined in System class that is used to send the request to JVM to perform garbage collection.

What is the purpose of the finalize() method?
Ans: finalize() method is invoked just before the object is garbage collected. It is used to perform cleanup processing.

Can unreferenced objects be referenced again?
Ans: Yes.

What kind of thread is the Garbage collector thread?
Ans: Daemon thread.

What is the difference between final, finally and finalize?
Ans:

Final: final is a keyword, final can be variable, method or class. You, can’t change the value of the final variable, can’t override the final method, can’t inherit the final class.
Finally: finally block is used in exception handling. Finally, the block is always executed.
finalize(): finalize() method is used in garbage collection.finalize() method is invoked just before the object is garbage collected. The finalize() method can be used to perform any cleanup processing.

What is the purpose of the Runtime class?
Ans: The purpose of the Runtime class is to provide access to the Java runtime system.

How will you invoke any external process in Java?
Ans: By Runtime.getRuntime().exec(?) method.

What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
Ans: The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.

What an I/O filter?
Ans: An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

What is serialization?
Ans: Serialization is a process of writing the state of an object into a byte stream. It is mainly used to travel object’s state on the network.

What is Deserialization?
Ans: Deserialization is the process of reconstructing the object from the serialized state. It is the reverse operation of serialization.

What is a transient keyword?
Ans: If you define any data member as transient, it will not be serialized.

What is Externalizable?
Ans: the Externalizable interface is used to write the state of an object into a byte stream in a compressed format. It is not a marker interface.

What is the difference between Serializable and Externalizable interface?
Ans: Serializable is a marker interface, but Externalizable is not a marker interface. When you use the Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serialization process. When you use Externalizable interface, you have complete control over your class’s serialization process.

What is a reflection?
Ans: Reflection is the process of examining or modifying the runtime behaviour of a class at runtime. It is used in:
IDE (Integrated Development Environment), e.g. Eclipse, MyEclipse, NetBeans. Debugger Test Tools etc.

Can you access the private method from outside the class?
Ans: Yes, by changing the runtime behaviour of a class if the class is not secured.

What are wrapper classes?
Ans: Wrapper classes are classes that allow primitive types to be accessed as objects.

What is a native method?
Ans: A native method is a method that is implemented in a language other than Java.

What is the purpose of the System class?
Ans: The purpose of the System class is to provide access to system resources.

What comes to mind when someone mentions a shallow copy in Java?
Ans: Object cloning.

What is a singleton class?
Ans: Singleton class means that at any given time only one instance of the class is present, in one JVM.

Java Interview Questions Core Java