java 单例模式的实现

最新推荐文章于 2025-02-15 11:01:31 发布

原创最新推荐文章于 2025-02-15 11:01:31 发布 · 147 阅读

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#java #单例模式

1. 懒汉

缺点：线程不安全

public class SingletonInstanceLazy {
    
    private SingletonInstanceLazy (){
    }
    
    private static SingletonInstanceLazy singletonInstanceLazy;
    
    public static SingletonInstanceLazy getInstance(){
        if(singletonInstanceLazy == null){
            singletonInstanceLazy = new SingletonInstanceLazy();
        }
        return singletonInstanceLazy;
    }
}

2. 饿汉

优点：线程安全

缺点：项目初始化会慢

public class SingletonInstanceHungry {

    private SingletonInstanceHungry(){
    }

    private static SingletonInstanceHungry singletonInstanceHungry = new SingletonInstanceHungry();

    public static SingletonInstanceHungry getInstance(){
        return singletonInstanceHungry;
    }
}

3. 双重检查锁

优点：线程安全

public class SingletonInstanceDoubleCheck {

    private SingletonInstanceDoubleCheck(){
    }

    private static volatile SingletonInstanceDoubleCheck singletonInstanceDoubleCheck;

    public static SingletonInstanceDoubleCheck getInstance(){
        if(singletonInstanceDoubleCheck == null){
            synchronized (singletonInstanceDoubleCheck){
                if(singletonInstanceDoubleCheck == null){
                    singletonInstanceDoubleCheck = new SingletonInstanceDoubleCheck();
                }
            }
        }
        return singletonInstanceDoubleCheck;
    }
}

4. 静态内部类

优点：线程安全，也不用提前加载

public class SingletonInstanceStaticInnerClass {

    private SingletonInstanceStaticInnerClass(){
    }
    
    private static class InnerClass{
        private static final SingletonInstanceStaticInnerClass INSTANCE = new SingletonInstanceStaticInnerClass();
    }

    public SingletonInstanceStaticInnerClass getInstance(){
        return InnerClass.INSTANCE;
    }
}

5. 枚举

优点：线程安全

public enum SingletonInstanceEnum {
    INSTANCE;
}