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; }}复制代码 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; }}复制代码 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; }}复制代码 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(); }}复制代码 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 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; }}复制代码 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(){}}复制代码 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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