线程安全的单例模式

package com.atguigu.java2;
/**
 * 使用同步机制将单例模式中的懒汉式改写为线程安全的
 *
 * @author Dxkstart
 * @create 2021-05-07 18:41
 */
public class BankTest {
    public static void main(String[] args) {
    }
}
class Bank {
    private Bank() {
    }
    private static Bank instance = null;
    public static Bank getInstance() {
        //方式一：效率稍差
//        synchronized (Bank.class) {
//            if(instance == null){
//                instance = new Bank();
//            }
//            return instance;
//        }
        //方式二；效率更高
        if (instance == null) {
            synchronized (Bank.class) {
                if (instance == null) {
                    instance = new Bank();
                }
            }
        }
        return instance;
    }
}