设计模式之单例模式

静态内部类实现

package com.haxianhe.singleton;

/**
 * 静态内部类
 */
public class Singleton5 {
    private Singleton5() {

    }

    private static class InstanceFactory {
        public static Singleton5 instance = new Singleton5();
    }

    public static Singleton5 getInstance() {
        return InstanceFactory.instance;
    }
}

饿汉模式

package com.haxianhe.singleton;
/**
 * 饿汉模式
 * */
public class Singleton4 {
    private Singleton4() {

    }

    private static Singleton4 instance = new Singleton4();

    public static Singleton4 getInstance() {
        return instance;
    }
}

懒汉模式（双重锁检测）

package com.haxianhe.singleton;

/**
 * 双重锁检测（懒汉模式）
 */
public class Singleton3 {
    /* 私有构造方法，防止被实例化 */
    private Singleton3() {

    }

    /* 私有实例变量，防止被引用 */
    private static Singleton3 instance = null;

    public static Singleton3 getInstance() {
        if (instance == null) {
            synchronized (instance) {
                if (instance == null) {
                    instance = new Singleton3();
                }
            }
        }
        return instance;
    }
}