Java Tutorial

This Java tutorial is tailored for newcomers, offering a journey from basic principles to complex Java programming techniques. Completing this tutorial equips you with a solid understanding of Java, preparing you for advanced learning. You'll emerge ready to tackle the challenges of becoming a top-tier software engineer, with the skills to innovate and excel in the vast world of software development.

Custom Exception
Java Custom Exception
The custom exception refers to the creation of your own exception to customize an exception according to the needs. The custom exceptions are derived from the Exception class.
Need of Java Custom Exceptions
To categorize the exceptions based on the different types of errors in your project.
To allow application-level exception handling.
Create a Custom Exception in Java
To create a custom exception, you need to create a class that must be inherited from the Exception class.
Syntax
Here is the syntax to create a custom class in Java 
class MyException extends Exception {
}
You just need to extend the predefined Exception class to create your own Exception. These are considered to be checked exceptions.
Rules to Create Custom Exception
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.
Java Custom Exception Example
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.
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.
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.
package com.tutorialspoint;
﻿
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();
      }
   }
}
﻿
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;
   }
}
﻿
class InsufficientFundsException extends Exception {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}
Output
Compile all the above three files and run BankDemo. This will produce the following result 
Depositing $500...
﻿
Withdrawing $100...
﻿
Withdrawing $600...
Sorry, but you are short $200.0
com.tutorialspoint.InsufficientFundsException
	at com.tutorialspoint.CheckingAccount.withdraw(BankDemo.java:39)
	at com.tutorialspoint.BankDemo.main(BankDemo.java:14)
In next example, we're declaring our custom exception as RuntimeException to make it as unchecked exception class as below
class MyException extends RuntimeException {
}
Example to Create Custom Class by Extending Runtime Exception
We are extending the predefined RuntimeException class to create your own Exception as an unchecked exception. The following InsufficientFundsException class is a user-defined exception that extends the RuntimeException class, making it a unchecked exception. An RuntimeException class is like any other class, containing useful fields and methods.
class InsufficientFundsException extends RuntimeException {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}
The following BankDemo program demonstrates invoking the deposit() and withdraw() methods of CheckingAccount using unchecked exception.
package com.tutorialspoint;
﻿
public class BankDemo {
﻿
   public static void main(String [] args) {
      CheckingAccount c = new CheckingAccount(101);
      System.out.println("Depositing $500...");
      c.deposit(500.00);
      
      System.out.println("\nWithdrawing $100...");
      c.withdraw(100.00);
      System.out.println("\nWithdrawing $600...");
      c.withdraw(600.00);
﻿
   }
}
﻿
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) {
      if(amount <= balance) {
         balance -= amount;
      }else {
         double needs = amount - balance;
         throw new InsufficientFundsException(needs);
      }
   }
   
   public double getBalance() {
      return balance;
   }
   
   public int getNumber() {
      return number;
   }
}
﻿
class InsufficientFundsException extends RuntimeException {
   private double amount;
   
   public InsufficientFundsException(double amount) {
      this.amount = amount;
   }
   
   public double getAmount() {
      return amount;
   }
}
Output
Compile and run BankDemo. This will produce the following result 
Depositing $500...
﻿
Withdrawing $100...
﻿
Withdrawing $600...
Exception in thread "main" 
com.tutorialspoint.InsufficientFundsException
	at com.tutorialspoint.CheckingAccount.withdraw(BankDemo.java:35)
	at com.tutorialspoint.BankDemo.main(BankDemo.java:13)
﻿
﻿
﻿
﻿

Java Tutorial

Java Control Statements

Object Oriented Programming

Java Built-in Classes

Java File Handling

Java Error & Exceptions

Java Multithreading

Java Synchronization

Java Networking

Java Collections

Java List Interface

Java Queue Interface

Java Map Interface

Java Set Interface

Java Data Structures

Java Collections Algorithms

Java Miscellaneous

Java Tutorial

Custom Exception

Java Custom Exception

Need of Java Custom Exceptions

Create a Custom Exception in Java

Syntax

Rules to Create Custom Exception

Java Custom Exception Example

Output

Example to Create Custom Class by Extending Runtime Exception

Output