implement singleton design pattern in java code example

Example 1: java singleton implementation

public class SingletonClass {
    private static final SingletonClass SINGLE_INSTANCE = new SingletonClass();
    private SingletonClass() {}
  public static SingletonClass getInstance() {
      return SINGLE_INSTANCE;
    }
}

Example 2: threadsafe singleton pattern in java

package com.journaldev.designpatterns;

public class ASingleton {

	private static volatile ASingleton instance;
	private static Object mutex = new Object();

	private ASingleton() {
	}

	public static ASingleton getInstance() {
		ASingleton result = instance;
		if (result == null) {
			synchronized (mutex) {
				result = instance;
				if (result == null)
					instance = result = new ASingleton();
			}
		}
		return result;
	}

}