Difference Between Throw and Throws in Java

Throw VS Throws in Java: In this article, we will discuss the difference between throw and throws clause in detail with a few examples.

Throw Clause or Throw Keyword

• the throw keyword is used to throw an exception explicitly
• It is used within the method to throw an exception explicitly
• It is generally used for throwing user-defined exception or custom exception
• Although, it is valid & possible to throw a pre-defined exception or already defined exception in Java too
• Maximum of only one exception can be thrown using throw keyword and it can be checked exception or unchecked exception or a user-defined exception
• the throw keyword is always followed by instance (i.e.; instance of any type of exception)

Syntax:

throw instanceOfExceptionType;

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• throws keyword is used to declare an exception, indicating the caller method to handle the exception whenever invoking
• with the usage of throws clause, any type of exception can be declared (i.e.; checked exception or unchecked exception or user-defined exception)
• Any number of the exception can be declared next to the method signature, with a comma (,) separating them
• throws keyword is always followed by class (this class must be a pre-defined exception or user-defined exception which must be a subclass of Throwable class or one of its sub-class)

Syntax:

access_modifier return_type method_name() throws exception_list;

Let us move on and discuss them on a one-on-one parameter in the tabular format

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Difference Between Throw VS Throws

Check Also: Checked vs Unchecked exception

Example of Throw and Throws Keyword

• Whenever checked exception (it may be a pre-defined or user-defined exception) is thrown explicitly using throw keyword, then it must be handled either using a try-catch block or throws clause. Therefore, we have used throws clause to delegate the exception responsibility to the caller method
• But whenever unchecked exception (it may be a pre-defined or user-defined exception) is thrown explicitly using throw keyword, then it is not necessary to handle. It is up to the choice of a programmer to handle it

Example 1: checked exception

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ThrowAndThrowsExample.java

import java.io.FileNotFoundException;
public class ThrowAndThrowsExample {
    public static void main(String[] args) throws FileNotFoundException {
        // must be surrounded with try-catch block compulsorily,
        // because we are invoking method throwing checked exception OR throws clause
        printFileContent();
    }
    // throwing checked exception
    public static void printFileContent() throws FileNotFoundException  {
        // assumed that, we are trying to access file from remote location
        // FileReader fileReader = new FileReader("D:/Folder/test.txt");
        throw new FileNotFoundException("File is not available");
        // further file processing
    }
}

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Example 2: unchecked exception

Explicitly throwing an exception using throw keyword

ThrowWithUncheckedExceptionExample.java

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public class ThrowWithUncheckedExceptionExample {
    public static void main(String[] args) {
        // invoking method
        anotherMethod(null);
    }
    public static void anotherMethod(String str) {
        if(str == null){
            throw new NullPointerException("Please send some valid Sgring");
        }
        // further processing with the string value
    }
}