1

单例模式的几种实现方法,具体如下:

懒汉模式

public class Singleton{
    private static Singleton instance;

    private Singleton(){
    }

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

优点

  • 可以延迟加载

缺点

  • 多线程不安全

饿汉模式

public class Singleton {
    private static Singleton instance = new Singleton();

    private Singleton(){}

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

优点

  • 多线程安全

缺点

  • 加载类时就初始化完成,无法延时加载

双重检查

public class Singleton {

    private static Singleton instance ;

    private Singleton(){}

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

优点

  • 多线程安全

  • 延迟加载

缺点

  • 同步耗时

静态内部类

public class Singleton {

    private Singleton(){}

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

    private static class SingletonHolder {
        private static Singleton instance = new Singleton();
    }
}

优点

  • 多线程安全

  • 延迟加载

  • 耗时短(与双重检查相比)

用缓存实现

public class Singleton {

    private static final String KEY = "instance";

    private static Map<String, Singleton> map = new HashMap<>();

    private Singleton(){}

    public static Singleton getInstance(){
        Singleton singleton ;
        if (map.get(KEY) == null){
            singleton = new Singleton();
            map.put(KEY, singleton);
        } else {
            singleton = map.get(KEY);
        }
        return singleton;
    }
}

优点

  • 线程安全

缺点

  • 占用内存较大

枚举模式

public enum Singleton {

    instance;

    public void operate(){}
}

优点

  • 简洁

缺点

  • 占用内存大(Android官方不推荐使用枚举)

更多文章请移步我的博客:DevWiki Bolg


DevWiki
387 声望25 粉丝