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Creating Own Exceptions in Java





The Java programming language allow us to create our own exception classes which are basically subclasses built-in class Exception.

To create our own exception class simply create a class as a subclass of built-in Exception class.

We may create constructor in the user-defined exception class and pass a string to Exception class constructor using super(). We can use getMessage() method to access the string.

Let's look at the following Java code that illustrates the creation of user-defined exception.

Example
import java.util.Scanner;

class NotEligibleException extends Exception{
    NotEligibleException(String msg){
        super(msg);
    }
}
        
class VoterList{            
    int age;            
    VoterList(int age){
        this.age = age;
    }
            
    void checkEligibility() {
        try {
            if(age < 18) {
                throw new NotEligibleException("Error: Not eligible for vote due to under age.");
            }
            System.out.println("Congrates! You are eligible for vote.");
        }
        catch(NotEligibleException nee) {
            System.out.println(nee.getMessage());
        }
    }
    public static void main(String args[]) {
        
        Scanner input = new Scanner(System.in);
        System.out.println("Enter your age in years: ");
        int age = input.nextInt();
        VoterList person = new VoterList(age);
        person.checkEligibility();
    }
}

When we run this code, it produce the following output.

creating own exception in Java