User Defined Exception in Java with Examples

In Java programming, it is possible to create our own exception and such exception are called user defined exception in Java.

Exception class is a predifine class. Any user defined exception created by us must be subclass of predefine Exception class and created by extending Exception class.

 The throw and throws keyword are used for implementing user defined exception. 

throw: throw keyword is used to throw an exception explicitly from a method or from a block.   

for instance

 Here new NumberIsGreaterException();

is creating new exception and throwing it.

throws: throws keyword is used with method signature that informs that the method can throw mentioned exception.   

Here Scanner is class and above mentioned Scanner represents the constructor call, On the constructor call of above we have to handle File not found Exception.

Steps for creating custom exception

  1. Create a class
  2. Extend the Exception class
  3. Create a String argument constructor to pass custom message.

Examples of User Defined Exception in Java

Example1:   write a program to take a number from user by using command line argument during run time. if user will enter  more than 100 then grnerate user defined exception MyException.

Explaination: In the above program, name of user define exception is NumberIsGreaterException. 

In the above program user enter  the number 111 during run time using command line argument.

Here value of “m” is greter than 100 therefore  “throw  newNumberIsGreaterException ();” this throw statement throw the exception and catch by catch block, but before thorw “NumberIsGreaterException ()” constructer will call.

Example: Create your own exception to check age is valid or not

InvalidAgeException.java

CheckAge.java

Output

Example: Write a Java program to check a time is in range or not, if time is not in range then throw custom exception.

InvalidTimeException.java

CheckTime.java

Output

Example: Write a program to create user defined exception in Java to check a given name exists or not. If name doesn’t exists then throw a custom exception.

InvalidNameException.java

CheckName.java

Output