user defined exceptions in java with example

The built-in exceptions in java are not able to describe a certain situation. In such cases, like the built-in exceptions, the user(programmer) can also create his own exceptions which are called 'User-defined exceptions'. The following steps are followed in creation of user-defined exceptions.
  • The user should create an exception class as a subclass to Exception class. Since all exceptions are subclasses of Exception class, the user should also make his class a subclass to it.
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class MyException extends Exception
  • The user can write a default constructor in his own exception class. He can use it in case he does not want to store any exceptions details. If the user does not want to create an empty object to his exception class, he can eliminate writing the default constructor.

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MyException() {}
  • The user can create a parametrised constructor with a string as a parameter. He can use this to store exception details. He can call super class (Exception) constructor from this and send the string there.
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MyException(String str){
    super(str);  //call exception class constructor and store str there.
}
  • When the user wants to raise his own exception, he should create an object to his exception class and throw it using throw clause,
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MyException me = new MyException("Exception Data");
throw me;

       Here is the example of user defined exception. Users can create their own exception classes by extending the Exception class and thrown by using the throw keyword.

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package com.javatbrains.exceptions;

/*This class represents the Users own exception class.*/
public class MyOwnException extends Exception {
     // store account information
     private static int acc[] = { 101, 102, 103, 104, 105 };

     private static String name[] = { "Subba", "Reddy", "Samba", "Rama", "Amar"};
     private static double bal[] = { 1000.00, 1200.00, 1290.00, 1500.00, 168.00 };

     // default constructor
     MyOwnException() {
     }

     // Parametrized Constructor
     MyOwnException(String str) {
          super(str);
     }

     // write main()
     public static void main(String[] args) {
          try{
              // display the heading from the table
              System.out.println("AccNo"+ "\t"+ "Customer"+ "\t"+ "Balance");

              // display actual account information
              for(inti = 0; i <5; i++) {
                   System.out.println(acc[i] + "\t"+ name[i] + "\t\t"+ bal[i]);

                   // display own exception if balance <1000
                   if(bal[i] <1000) {
                        MyOwnException me = new MyOwnException(
                                  "Balance amount is less");
                        throwme;
                   }
              }
          } catch(MyOwnException me) {
              me.printStackTrace();
          }
     }

}
OutPut:
      AccNo   Customer   Balance
       101     Subba     1000.0
       102     Reddy     1200.0
       103     Samba     1290.0
       104     Rama      1500.0
       105     Amar      168.0
      com.javatbrains.exceptions.MyOwnException: Balance amount is less
     at     com.javatbrains.exceptions.MyOwnException.main(MyOwnException.java:32)

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