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)

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