About singleton patterns in Java

A. Features:

① Singleton class can have only one instance

② Singleton classes must create their own unique instances themselves

③ Singleton class must provide this instance to all other objects

Two. Implementation method:

① a hungry man type

public class singleton1{Private Singleton1 ();    private static Singleton1 single=new Singleton1 ();    public static final Singleton1 getinstance () {return single; } }

② Lazy 1 (thread insecure)

public class singleton1{Private Singleton1 ();    private static Singleton1 Single=null;         public static Singleton1 getinstance () {if (single==null) {single=new Singleton1 ();     } return single; } }

This approach is because no lock is added to the GetInstance method, and it produces multiple Singleton1 instances when multiple threads are accessing the method at the same time.

③ Lazy 2 (thread-safe, but inefficient, that is, adding a thread lock [the place where the lock is a waste of time, if you can reduce the determination of the lock can save time])

public class singleton1{Private Singleton1 ();    private static Singleton1 Single=null;         public static synchronized Singleton1 getinstance () {if (single==null) {single=new Singleton1 ();     } return single; } }

④ Lazy 3 (thread-safe, high-efficiency, double-judge)

  public class singleton1{    private singleton1 ();     private static singleton1 single=null;    public static  singleton1 getinstance () {        if (single==null) {             synchronized (Singleton1.class) {                     if (Single==null) {                         s=new singleton1 ();                      }              }               }         return single;      } }

About singleton patterns in Java