Singleton Pattern

Singleton pattern is the simplest pattern in java and is under the creational pattern. some key points to use in singleton pattern.

• It is static in nature
• private constructor
• private static instance of the class
• public static getter method
• no parameters to the constructor

create singleton class

public class Singleton {
    private static Singleton object = null;
    private Singleton() {
    }
    public static Singleton getInstance() {
        if (object == null) {
            object = new Singleton();
        }
        return object;
    }
    public void showMessage() {
        System.out.println("Singleton Pattern");
    }
}

create demo class

public class Demo {
    public static void main(String[] args) {
        Singleton object = Singleton.getInstance();
        object.showMessage();
    }
}

but this classic implementation not thread safe. therefore using synchronized make sure that the one thread can execute the getInstance();at one time.
As this;

public class Singleton {
    private static Singleton object = null;
    private Singleton() {
    }
    public static synchronized Singleton getInstance() {
        if (object == null) {
            object = new Singleton();
        }
        return object;
    }
}