Checked Exception VS Unchecked Exception In Java

Checked Exception VS Unchecked Exception In Java

In this article, we will discuss checked and unchecked exception in detail with explanation & examples and also list some of the most commonly known checked & unchecked exception.

Checked Exception

• An exception which is checked at compile-time during compilation is known as Checked Exception
• Alternate definition: any line of code that could throw an exception, and if it is raised to handle during compilation is said to be checked exception
• For example, accessing a file from a remote location could throw a file not found an exception
• It is the programmer’s responsibility to handle the checked exception for successful compilation
• This way, if an exception is raised during execution, then respective handling code will be executed
• Note: if it isn’t handled then the program will throw a compile-time error
• Example: IOException, FileNotFoundException, InterruptedException, SQLException, etc
• Except for Runtime exception & its child classes and error & its child classes, all other exceptions fall under the category of Checked Exception

CheckedException.java

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import java.io.BufferedReader;
import java.io.FileReader; 
public class CheckedException { 
    public static void main(String[] args) 
{
        FileReader fileReader = new FileReader("F:\\BenchRes.txt");   
        BufferedReader bufferedReader = new BufferedReader(fileReader);    
 
        // logic for reading    
    }
}

Output:

Compile-time error: Unhandled exception type FileNotFoundException

Checked exception screen-capture from Eclipse IDE:

Unchecked Exception

• An exception which is NOT checked at compile-time is known as Unchecked Exception
• Alternate definition: any line of code that could throw an exception at runtime is said to be an unchecked exception
• An unchecked exception is because of a programming error
• For example, accessing out of index position to assign some value during execution could throw an exception at runtime
• So, it is again the programmer’s responsibility to handle the unchecked exception by providing an alternate solution in the exception handling code
• Note: if it isn’t handled properly then the program will terminate abnormally at runtime
• Example: Runtime exception & its child classes and error & its child classes are examples of Unchecked Exception
• Like ArithmeticException, NullPointerException, NumberFormatException, ArrayIndexOutOfBoundsException, StatckOverflowError, etc

UncheckedException.java

public class UncheckedException {
 
    public static void main(String[] args) {
 
        char[] ch = new char[4];
        ch[7] = 'B';
 
        System.out.println(ch);
    }
}

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7
    at in.bench.resources.exception.handling.UncheckedException.main(UncheckedException.java:8)

The misconception about the checked and unchecked exception:

• Sometimes, a checked exception is also referred to as a compile-time exception, and unchecked exception are referred to as runtime exception
• But this is misleading because every exception (whether it is checked or unchecked) occurs/raised only at the runtime, i.e., during program execution-only
• Reason: during compilation; the checked exception is caught and raises a compile-time error, due to which programmer has to handle the exception by providing either try-catch blocks or using throws keyword
• Whereas unchecked exception isn’t caught during compilation, rather it raises an exception during execution because of a programming error