How to Create a Custom Exception in Java

We can create a custom exception class by extending the Exception class and implementing the constructors.

public class CustomException extends Exception {}

1. Creating a custom exception#

We’ll want to ensure we implement every constructor listed in the Constructor Summary of the Exception documentation.

public class CustomException extends Exception {
  public CustomException() {}
  public CustomException(String message) {
    super(message);
  }
  public CustomException(Throwable cause) {
    super(cause);
  }
  public CustomException(String message, Throwable cause) {
    super(message, cause);
  }
}

In particular, we’ll want the last two constructors (i.e. Throwable(Throwable), Throwable(String, Throwable)) to support chained exceptions, which is very useful ƒor debugging.

2. Using the custom exception#

We can throw our custom exception just as we would any other exception.

try {
  if (/* Reason for exception */) {
    throw new CustomException();
  }
} catch(CustomException ex) {
  // Process exception
}