How to create a custom unchecked exception in Java?

We can create the custom unchecked exception by extending the RuntimeException in Java.

Unchecked exceptions inherit from the Error class or the RuntimeException class. Many programmers feel that we cannot handle these exceptions in our programs because they represent the type of errors from which programs cannot be expected to recover while the program is running. When an unchecked exception is thrown, it is usually caused by misuse of code, passing a null or otherwise incorrect argument.

Syntax

public class MyCustomException extends RuntimeException {
   public MyCustomException(String message) {
      super(message);
   }
}

Implementing an Unchecked Exception

The implementation of a custom unchecked exception is almost similar to a checked exception in Java. The only difference is that an unchecked exception has to extend RuntimeException instead of Exception.

Example

public class CustomUncheckedException extends RuntimeException {
   /*
   * Required when we want to add a custom message when throwing the exception
   * as throw new CustomUncheckedException(" Custom Unchecked Exception ");
   */
   public CustomUncheckedException(String message) {
      // calling super invokes the constructors of all super classes
      // which helps to create the complete stacktrace.
      super(message);
   }
   /*
   * Required when we want to wrap the exception generated inside the catch block and rethrow it
   * as catch(ArrayIndexOutOfBoundsException e) {
      * throw new CustomUncheckedException(e);
   * }
   */
   public CustomUncheckedException(Throwable cause) {
      // call appropriate parent constructor
      super(cause);
   }
   /*
   * Required when we want both the above
   * as catch(ArrayIndexOutOfBoundsException e) {
      * throw new CustomUncheckedException(e, "File not found");
   * }
   */
   public CustomUncheckedException(String message, Throwable throwable) {
      // call appropriate parent constructor
      super(message, throwable);
   }
}