java常用设计模式--单例模式简单例子

Posted 2021-01-18 MsencSir

package com.ruanyun;

/**
 * @Auther: maxw
 * @Date: 2018/11/10 17:29
 * @Description:
 */
public class Test4 {
    public static void main(String args[]){
        F99 f99  = F99.getInstance();
        F99 f100 = F99.getInstance();
        System.out.println(f99==f100);
    }
}
//假设 F99战机 只有一架
class F99{
    //懒汉模式
 /*   private volatile static F99 f99;
    private F99() {
    }
    public static synchronized F99 getInstance(){
        if(f99 == null){
            f99 = new F99();
        }
        return f99;
    }*/
    //饿汉模式
    /*private static final F99 f99 = new F99();
    private F99() {
    }
    public static F99 getInstance(){
        return f99;
    }*/
    //双重锁模式
    /*private volatile static F99 f99;
    private F99() {
    }
    public static F99 getInstance(){
        if(f99==null){
            synchronized (F99.class){
                if(f99==null){
                    f99 = new F99();
                }
            }
        }
        return f99;
    }*/
    //静态内部类模式 最优写法
    private static class innerClass{
        private static final F99 f99 = new F99();
    }
    public static F99 getInstance(){
        return innerClass.f99;
    }
    //还有一种方法 枚举 在此不再展示
}