Java Singleton

In this tutorial, we will learn about the singleton design pattern and how to apply it in Java with the help of examples.

The singleton pattern is one of the simplest design patterns. Sometimes we need to have only one instance of our class .

Java Singleton

Here's how we can use singletons in Java.
• create a private constructor that restricts to create an object outside of the class.
• create a private attribute that refers to the singleton object.
• create a public static method that allows us to create and access the object we created. Inside the method, we will create a condition that restricts us from creating more than one object.

Here's an example.

class SingletonExample {

// private field that refers to the object
   private static SingletonExample singleObject;

   private SingletonExample() {
      // constructor of the SingletonExample class
   }

   public static SingletonExample getInstance() {
      // write code that allows us to create only one object
      // access the object as per our need
   }
}

In the above example,

• private static SingletonExample singleObject - a reference to the object of the class.
• private SingletonExample() - a private constructor that restricts creating objects outside of the class.
• public static SingletonExample getInstance() - this method returns the reference to the only object of the class. Since the method static, it can be accessed using the class name.

Use of Singleton Class

In Java, Singleton class is a class that controls the object creation. It means the singleton class allows us to create a single object of the class, at a time. It is usually used to control access to resources, such as database connections or sockets. It ensures that only one connection is made and a thread can access the connection at a time.

Advantages

• Singleton controls concurrent access to the resource.
• It ensures there is only one object available across the application in a controlled state.

Difference Between Singleton Class and Normal Class

The main difference between these two classes is an instantiation. To create an instance of a normal class, we use a constructor. On the other hand, to create an instance of a singleton class, we use getInstance() method.
Generally, we use the class name as the method name. It avoids confusion.