Implementation of Java single case schema data collation _java

The implementation of Java Single example mode , several methods of Java single example mode are sorted out:

Single case mode It's written in many books:

public class SingleTon1 {
   
  private SingleTon1 () { 
  }
 
  private static SingleTon1 instance = null;
 
   
  public static SingleTon1 getinstance () {
    if (instance = null) {
      instance = new SingleTon1 ();
    }
    return instance
  }
}

But the actual development is not so written, because there is a serious problem, multithreading concurrent access, may produce multiple instances!!

Here are a few common methods:

1. Use the Synchronized keyword

Package Singleton;
 
public class SingleTon1 {
   
   
  private SingleTon1 () {
     
  }
 
  private static SingleTon1 instance = null;
   
  Multithreading problem solution one, but not high efficiency! Because every call will lock! Public
  static synchronized SingleTon1 getinstance () {
    if (instance = = null) {
      instance = new SingleTon1 ();
    return
    instance;
  }
  public void print () {
    System.out.println ("thread_id:" +thread.currentthread (). GetId ());
  }
   
  private static Object = new Object ();
  The ingenious method is to add a lock on null and then not add public
  static SingleTon1 GetInstance2 () {
     
    if (instance = null) {
      Synchronized (object) {
        instance = new SingleTon1 ();
      }
    }
    return instance
  }
 
}

2. Add lock

Package Singleton;
 
Import Java.util.concurrent.locks.ReentrantLock;
 
public class SingleTon2 {
   
  private SingleTon2 () {
     
  }
  private static Reentrantlock lock = new Reentrantlock (); C6/>private static SingleTon2 instance = null;
   
   
  public void print () {
    System.out.println ("thread_id:" +thread.currentthread (). GetId ());
  }
   
  public static SingleTon2 GetInstance2 () {
     
    if (instance = null) {
      lock.lock ();
      if (instance = null) {//Note here also to judge!!
        instance = new SingleTon2 ();
      }
      Lock.unlock ();
    }
    return instance
  }
}

3. Using static variables:

Package Singleton;
 
 
public class SingleTon3 {public
   
  static void print () {
    System.out.println ("thread_id:" +thread.currentthread () . GetId ());
   
  public static Nested getnested () {return
   
    nested.instance;
  }
  This is a single instance of the class static classes created
  nested{
   private Nested () {
    }
  static Nested instance = new Nested ();
  }
}

These are the common patterns for creating a single example:

Test code:

 package singleton; Import Singleton.
 
singleton3.nested; public class Test2 {public static void main (string[] args) {//TODO auto-generated a stub Nested single
    ton
    myrunnable mm = new myrunnable ();
     
    Myrunnable m1 = new myrunnable ();
    Myrunnable2 m2 = new Myrunnable2 ();
    New Thread (M1). Start ();
    New Thread (M2). Start ();
    if (M1.singleton = = M2.singleton) {//Is the same System.out.println ("is the same");
    }else{System.out.println ("not the same");
      }} class Myrunnable implements runnable{Nested Singleton; 
        @Override public void Run () {//TODO auto-generated method Stub singleton = singleton3.getnested ();
      Singleton3.print ();
    } class Myrunnable2 implements runnable{Nested Singleton;
      @Override public void Run () {//TODO auto-generated method Stub singleton = singleton3.getnested ();
    Singleton3.print (); }
  }

Output:

is the same

Thread_id:11
Thread_id:10

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