What is nested try-catch block?

Nested try-catch block means a try-catch block containing another try-catch block. In some cases, part of a block can cause one error and the entire block can cause another. In such cases, Java allows us to enclose a try catch in another try catch block which is known as nested try-catch block.

Syntax

try {
    
    Statement 1
    Statement 2
    Statement 3
    
    // A nested try catch block
    try {
        
        // Body of nested try block.
        
    } catch(<exception_class> <object_name>) {
        // Body of nested catch block.
    }
    Statement N

} catch (<exception_class> <object_name>) {
    // Body of parent catch block.
}

Example 1

In the following example program, one nested try-catch block is created to handle unexpected null pointer exception and the outer exception can handle any type of checked/unchecked exceptions.

NestedTryCatchExample1.javaCopy
public class NestedTryCatchExample1 {

    public static void main(String[] args) {

        try {

            String str = null;
            int length = 0;

            try {

                length = str.length();

            } catch (NullPointerException ex) {

                // Handle the nested exception here.
                System.out.println("Oops string is not looking good!");
            }

            System.out.println("Length of a string: " + length);

        } catch (Exception ex) {

            // Handle any type of exception here.
            System.out.println("Unknown exception!");
        }

    }
}
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Example 2

The following program is just similar to the above one, but here nested try-catch block is not capable to handle the exception so it is passing the exception to the parent catch block.

NestedTryCatchExample2.javaCopy
public class NestedTryCatchExample2 {

    public static void main(String[] args) {

        try {

            int numA = 1000;
            int numB = 0;
            int result = 0;

            // It can only handle null pointer exception
            try {

                // Divide a number by zero.
                result = numA / numB;

            } catch (NullPointerException ex) {

                // Handle the nested exception here.
                System.out.println(ex);
            }

            System.out.println("Result is: " + result);

        } catch (Exception ex) {

            // Handle any type of exception here.
            System.out.println("Unknown exception!");
        }

    }
}
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