How to create a custom exception in Java

Why we need custom Exception ?

How to create a custom exception ?

Write code to create a Custom Exception

All these are questions usually asked in a Java interview .So my today's post on how to create a custom exception in java .

As we know There are two types of Exception :

1. Checked Exception

2. Unchecked Exception

Both these exceptions have a common parent class Exception .So ,in same order if we have to create a custom exception ,we need to extend Exception class.

Ok , let me explain the process step by step .

1. Any custom exception should extend Exception Class .

2. There should be a proper name given to the Exception ,For example if there is an exception related to Invalid age name can be given as InvalidAgeException

public class InvalidAgeException extends Exception {}

public class InvalidAgeException extends Exception { private int age; public InvalidAgeException () { super(); } public InvalidAgeException (String message, int age) {    super(message);    this.age = age; }  }

In the above way we can define two constructors of InvalidAgeException with message and without message

Usage of custom Exception:

Below is the program with usage of custom exception.

public class CustomExceptionDemo  {  private static final Map<Integer, String> employee = new HashMap<>();  static  {    employee.put(100, "Mahesh");   employee.put(101, "Suresh");    employee.put(102, "Bran");    employee.put(103, "Troy"); }  public static void main(String args[])  {       CustomExceptionDemo t = new CustomExceptionDemo();     t.getAge(1000); }  public String getAge(int age)  {       if (employee.get(age) == null) {     throw new InvalidAgeException ("No such employee exists", age); } return employee.get(name); } }