学习是件开心事

单例模式

发表于

如果一个类比较特殊，实例只能有一个，不能让调用方自行new来创建对象，而是提供一个接口来返回该实例。这种设计理论被称为单例模式。

懒汉式

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public class Singleton {
    private static Singleton singleton;
    private Singleton() {
    }
    //懒汉式线程不安全
    public static Singleton getSingleton() {
        if (singleton == null) {
            singleton = new Singleton();
        }
        return singleton;
    }
    //懒汉式线程安全
    public static synchronized Singleton getSingleton2() {
        if (singleton == null) {
            singleton = new Singleton();
        }
        return singleton;
    }
}

饿汉式

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public class Singleton {
    private static Singleton singleton = new Singleton();
    private Singleton() {
    }
    public static Singleton getSingleton() {
        return singleton;
    }
}

静态内部类

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public class Singleton {
    private static class SingletonHolder {
        private static final Singleton INSTANCE = new Singleton();
    }
    private Singleton() {
    }
    public static Singleton getSingleton() {
        return SingletonHolder.INSTANCE;
    }
}