java--单例模式

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单例模式

设计为私有构造方法，不允许对象被new出来
这是一种创建型模式，主要用来创建只需要创建一次的对象，比如数据库连接，线程池创建等。

分类

按加载顺序分“懒汉”与“饿汉”式
按线程安全也可分为线程安全与非线程安全

package com.carl.singleton;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public final class ThreadPoolDirectLoad {    private static ExecutorService threadPool = Executors.newFixedThreadPool(5);    private ThreadPoolDirectLoad() {    }    public static ExecutorService getThreadPool() {        return threadPool;    }}

package com.carl.singleton;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public final class ThreadPoolLazyLoad {    private ThreadPoolLazyLoad() {    }    public static ExecutorService getThreadPool() {        return Help.threadPool;    }    private static class Help {        private static ExecutorService threadPool = Executors.newFixedThreadPool(5);    }}

package com.carl.singleton;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public final class ThreadPoolFactory {    private enum ThreadPoolEnum {        INSTANCE;        private ExecutorService threadPool;        private ThreadPoolEnum() {            threadPool = Executors.newFixedThreadPool(5);        }        public ExecutorService getInstance() {            return threadPool;        }    }    public static ExecutorService getInstance() {        return ThreadPoolEnum.INSTANCE.getInstance();    }}

其他

另外还有通过锁实现的懒汉与饿汉式，相对复杂些，工作中很少使用，

同样是达到线程安全的目的，我更喜欢枚举实现

https://testerhome.com/topics/10042

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