User defined exception in java
An exception is a problem that arises during the execution of a program. An exception can occur for many different reasons, including the following:
A user has entered invalid data.
A file that needs to be opened cannot be found.
A network connection has been lost in the middle of communications, or the JVM has run out of memory.
Some of these exceptions are caused by end user error, others by programmer error, and others by physical resources that have failed in some manner.Though Java provides an extensive set of in-built exceptions, there are cases in which we may need to define our own exceptions in order to handle the various application specific errors that we might encounter
In Java,Exceptions have been Categorized in two ways:
1. Java’s Built-In Exceptions
2. Custom Exceptions also called as User-Defined Exception
All Checked and Unchecked Exceptions are Java’s Built-In Exceptions.
You can create own customized exception as per requirements of the application. We know that for each application there are specific constraints. For Example, In case of Air Flight Booking, a passenger must specify the source ,destination place and age. Passenger must brings a ticket who is above the age of 3 years. Thus,Error-handling become necessary while developing a constraint application The Exception class and its subclass in java is not able to meet up the required constraint in application. For this, you create your own customized Exception to over address these constraints and ensure the integrity in the application
Developer can able to create their Own Exception Class by :
1.Extending the Exception class.
2.And the toString() method should be overridden in the user defined exception class in order to display meaningful information about the exception.
3.If want to write a checked exception that is automatically enforced by the Handle or Declare Rule, you need to extend the Exception class.
4.If want to write a runtime exception, you need to extend the RuntimeException class.
We can define our own Exception class as below:
class MyException extends Exception{
}
EXAMPLE:
Lets create an Exception class to handle age given in negative value.
NegativeAgeException.java
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public class NegativeAgeException extends Exception { private int age; public NegativeAgeException(int age){ this.age = age; } public String toString(){ return "Age cannot be negative" + " " +age ; } } |
CustomExceptionTest.java
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public class CustomExceptionTest { public static void main(String[] args) throws Exception{ int age = getAge(); if (age < 0){ throw new NegativeAgeException(age); }else{ System.out.println("Age entered is " + age); } } static int getAge(){ return -10; } } |
In the CustomExceptionTest class, the age is expected to be a positive number.
It would throw the user defined exception NegativeAgeException if the age is assigned a negative number.
At runtime, we get the following exception since the age is a negative number:
Exception in thread “main” Age cannot be negative -10
at com.j2eerference.corejava.exception.CustomExceptionTest.main(CustomExceptionTest.java:10)
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