解决单例模式懒汉式的线程安全问题

解决单例模式懒汉式的线程安全问题的几种办法

方法一：利用同步方法

将getInstance（）作为同步方法

class Bank{

    private Bank(){}

    private static Bank instance = null;

    //同步方法  
public static synchronized Bank getInstance(){

            if (instance == null){

                instance = new Bank();
            }

            return instance;
}

方法二：利用同步代码块

同步代码块中可以有两种写法，一种效率较好。

class Bank{

    private Bank(){}

    private static Bank instance = null;

public static  Bank getInstance(){

    //方式一：效率稍差
        synchronized (Bank.class) { //同步代码块

            if (instance == null){

                instance = new Bank();
            }

            return instance;
        }
}

    

class Bank{

    private Bank(){}

    private static Bank instance = null;

public static  Bank getInstance(){
//方式二：先判断instance是否为null
    if (instance == null) {
        
            synchronized (Bank.class) {
                
                if (instance == null) {
                    instance = new Bank();   
                }
            }
        }
    return instance;

    }
}