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Thread: Declaring your own exceptions

  1. #1

    Default Declaring your own exceptions

    You can create your own exceptions in Java. Keep the following points in mind when writing your own exception classes:

    * All exceptions must be a child of Throwable.
    If you want to write a checked exception that is automatically enforced by the Handle or Declare Rule, you need to extend the Exception class.
    * If you 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{ 
     }

    You just need to extend the Exception class to create your own Exception class. These are considered to be checked exceptions. The following InsufficientFundsException class is a user-defined exception that extends the Exception class, making it a checked exception. An exception class is like any other class, containing useful fields and methods.

    Example:

     // File Name InsufficientFundsException.java
     import java.io.*;
     
     public class InsufficientFundsException extends Exception 
     {
       private double amount;
       public InsufficientFundsException(double amount)
       {
          this.amount = amount;
       } 
       public double getAmount()
       {
          return amount;
       }
     }


    To demonstrate using our user-defined exception, the following CheckingAccount class contains a withdraw() method that throws an InsufficientFundsException.

     // File Name CheckingAccount.java
     import java.io.*;
     
     public class CheckingAccount
     {
       private double balance;
       private int number;
       public CheckingAccount(int number)
       {
          this.number = number;
       }
       public void deposit(double amount)
       {
          balance += amount;
       }
       public void withdraw(double amount) throws InsufficientFundsException 
       {
          if(amount <= balance)
          {
             balance -= amount;
          }
          else
          {
             double needs = amount - balance;
             throw new InsufficientFundsException(needs); 
          }
       }
       public double getBalance()
       {
          return balance;
       }
       public int getNumber()
       {
          return number;
       }
     }


    The following BankDemo program demonstrates invoking the deposit() and withdraw() methods of CheckingAccount.

     // File Name BankDemo.java
     public class BankDemo
     {
       public static void main(String [] args)
       {
          CheckingAccount c = new CheckingAccount(101);
          System.out.println("Depositing $500...");
          c.deposit(500.00);
          try
          {
             System.out.println("\nWithdrawing $100..."); 
             c.withdraw(100.00);
             System.out.println("\nWithdrawing $600...");
             c.withdraw(600.00);
          }catch(InsufficientFundsException e)
          {
             System.out.println("Sorry, but you are short $"
                                      + e.getAmount());
             e.printStackTrace();
          }
        }
     }
     
     
     
    //Compile all the above three files and run BankDemo, this would produce following result:
     
    Depositing $500...
     
    Withdrawing $100...
     
    Withdrawing $600...
    Sorry, but you are short $200.0
    InsufficientFundsException
            at CheckingAccount.withdraw(CheckingAccount.java:25)
            at BankDemo.main(BankDemo.java:13)

    Source Code 2 Learn
    Last edited by weakprogrammer; June 25th, 2011 at 03:50 PM.
    Warm Regards,

    weakprogrammer

    Code 2 Learn


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Declaring your own exceptions

    Please wrap your code segments in code tags to preserver formatting. Use the # icon in Advanced.

  3. #3

    Default Re: Declaring your own exceptions

    dONE norm.

    Thanks for telling.
    Warm Regards,

    weakprogrammer

    Code 2 Learn

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Declaring your own exceptions

    Thanks. Many of us find code easier to read if its formatted.

  5. #5
    mmm.. coffee JavaPF's Avatar
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    Default Re: Declaring your own exceptions

    I've updated the tags to the highlight tag as the syntax highlighting makes it even easier to read.. Ideally I would like to replace the code tag with this completely.

    As for this example on Exceptions, thanks for the post. I think people will indeed find this useful

    I notice you run a blog. Feel free to contact me if you wish to host a blog here.
    Please use [highlight=Java] code [/highlight] tags when posting your code.
    Forum Tip: Add to peoples reputation by clicking the button on their useful posts.

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