Java设计模式---单例模式

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