Java-单例模式

package com.example.demo.dataStructure.designPatten.singleTon;

/**
* 单例模式-懒汉式
*/
public class SingletonDemo1 {
private static SingletonDemo1 instance = null;

private SingletonDemo1() {}

public static SingletonDemo1 getInstance() {

// 真正用到的时候在实例化
if(instance == null) {
instance = new SingletonDemo1();
}
return instance;
}

}

package com.example.demo.dataStructure.designPatten.singleTon;

/**
* 单例模式-饿汉式
*/
public class SingletonDemo2 {
private static SingletonDemo2 instance = new SingletonDemo2(); // 类加载的时候实例化

private SingletonDemo2() {}

public static SingletonDemo2 getInstance() {
return instance;
}

}

package com.example.demo.dataStructure.designPatten.singleTon;

public class Test {
public static void main(String[] args) {
// 起10个线程
for (int i = 0; i < 10; i++) {
new TestThread().start();;
}
}
}

class TestThread extends Thread {
@Override
public void run() {
int hash = SingletonDemo1.getInstance().hashCode();// 更换类名来获取不同的实例
System.out.println(hash);
}
}

 1 package com.example.demo.dataStructure.designPatten.singleTon;
 2 
 3 /**
 4 * 双重检验懒汉式
 5 * */
 6 public class SingletonDemo3 {
 7 private static volatile SingletonDemo3 instance = null; // volatile 关键字作用
 8 
 9 private SingletonDemo3() {}
10 
11 public static SingletonDemo3 getInstance() {
12 if(instance == null) {
13 synchronized (SingletonDemo3.class) {
14 if(instance == null) {
15 instance = new SingletonDemo3();
16 }
17 }
18 }
19 return instance;
20 }
21 
22 }

 1 package com.example.demo.dataStructure.designPatten.singleTon;
 2 
 3 public class SingletonDemo4 {
 4 private SingletonDemo4() {}
 5 
 6 private static class CreInstance {
 7 private static SingletonDemo4 instance = new SingletonDemo4();
 8 }
 9 
10 public static SingletonDemo4 getInstance() {
11 return CreInstance.instance;
12 } 
13 }

package com.example.demo.dataStructure.designPatten.singleTon;

public enum SingletonDemo5 {
INSTANCE;
}