单例模式

/**
 *  
 *  @author devin
 *  @date 2021-01-08 11:12
 *  @version 1.0.2
*/
public class SingleTest {

    private static volatile SingleTest instance;

    private SingleTest(){
        System.out.println("create method");
    }

    //在这里加同步太重
    public static  SingleTest getInstance(){
        if(instance == null){
            synchronized (SingleTest.class){
                if(instance == null){
                    return instance = new SingleTest();
                }
            }
        }

        return instance;

    }

    public static void main(String[] args) {
        for(int i = 0;i < 1000;i++){
            new Thread(){
                @Override
                public void run() {
                    SingleTest.getInstance();
                }
            }.start();
        }

    }
}