Throwing and re-throwing an Exception in Java

When an exception is thrown, it is propagated up the call stack until it is caught by a try-catch block. If the exception is not caught, the program will terminate. Re-throwing an exception means throwing the same exception again after it has been caught in a try-catch block.

This can be useful for a number of reasons, such as:

• To pass the exception on to a higher-level method that can handle it.
• To add additional information to the exception object.
• To prevent the program from terminating.

Following is an example of how to throw and re-throw an exception in Java:

public class ExceptionDemo {

    public static void main(String[] args) {
        try {
            // This method will throw an exception.
            throw new RuntimeException("This is an exception");
        } catch (RuntimeException e) {
            // Add some additional information to the exception object.
            e.setMessage("This is a more detailed message");

            // Re-throw the exception.
            throw e;
        }
    }
}

Following are some additional things to keep in mind when throwing and re-throwing exceptions in Java:

• When we re-throw an exception, we must use the throw keyword.
• We can only re-throw an exception that has been caught in a try-catch block.
• If we re-throw an exception, the stack trace will be preserved.
• We can wrap an exception in another exception when we re-throw it. This is known as exception chaining.

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