设计模式单例

最新推荐文章于 2023-07-26 17:18:18 发布

原创最新推荐文章于 2023-07-26 17:18:18 发布 · 311 阅读

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文章标签：

#设计模式 #java #singleton

设计模式专栏收录该内容

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Singleton设计模式

1.使用时生成(非线程安全)

java code

class Singleton {

    private static Singleton instance = null;

    private Singleton() {}

    public static Singleton getInstance() {

        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

public class SingletonMode {

    public static void main(String[] args) {

        Singleton instance1 = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();

        if (instance1 == instance2) {
            System.out.println("singleton");
        } else {
            System.out.println("not singleton");
        }
    }
}

修改获得实例方法来保证线程安全

1 使用方法同步

java code

public static synchronized Singleton getInstance() {

    if (instance == null) {
        instance = new Singleton();
    }
    return instance;
}

2 使用类实例同步

java code

public static Singleton getInstance() {

    if (instance == null) {
        synchronized (Singleton.class) {
            instance = new Singleton();
        }
    }
    return instance;
}

2.初始化加载(线程安全)

java code

class Singleton {

    private static final Singleton instance = new Singleton();

    private Singleton() {}

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

public class SingletonMode {

    public static void main(String[] args) {

        Singleton instance1 = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();

        if (instance1 == instance2) {
            System.out.println("singleton");
        } else {
            System.out.println("not singleton");
        }
    }
}