Java design mode-singleton Mode

The first form: defines a class. Its constructor is private. It has a static private class variable. When the class is initialized, use a public getInstance method to obtain its reference, and then call the method. In this way, a new instance is required each time: public class Singleton {private static Singleton singleton = new Singleton (); public static Singleton getInstance () {return singleton ;}}. Method 2: class Singleton1 {private static Singleton1 singleton = null; public static Singleton1 getInstance () {if (singleton = null) singleton = new Singleton1 (); return singleton ;}} this method does not need to create an object every time.