Singleton Class Implementation in JAVA

Introduction

This repository contains a Java implementation of the Singleton design pattern. The Singleton pattern ensures that a class has only one instance. This can be useful in scenarios where you want to restrict the instantiation of a class to a single object.

Type-1 implementation: This implementation restricts the user to create more than one object of the singleton class.

Type-2 implementation: In this implementation every object of the singleton class points to the same memeory location.

How to compile

1. Go inside Type-1 or Type-2 directory.

cd Type-1

or,

cd Type-2

2. Compile using java compiler.

javac singleton.java

🗃️ Note: This will create two .class files inside current directory: Singleton.class & Main.class

How to run

• Run using java interpreter.

java Main

Output

• for Type-1 implementation

Object has been created!
This is a singleton class! Cannot create more objects!
This is a singleton class! Cannot create more objects!
1
Exception in thread "main" java.lang.NullPointerException: Cannot read field "id" because "<local2>" is null
        at Main.main(singleton.java:30)

• for Type-2 implementation

1
1
1