示例代碼:
1、餓漢單例模式 :
package com.example.imageloader;public class CEO {
private static final CEO mCeo = new CEO();
private CEO(){
}
public static CEO getCeo(){
return mCeo;
}
}
2、懶漢模式:
package com.example.imageloader;
public class Singleton {
private static Singleton instance;
private Singleton(){};
public static synchronized Singleton getInstance(){
if(instance == null){
instance = new Singleton();
}
return instance;
}
}
懶漢單例模式的有點事單例只有在使用時纔會被實例化,在一定程度上節約了資源;缺點是第一次加載時需要及時進行實例化,反應稍慢,最大的問題是每次調用getInstance都進行同步,造成不必要的同步開銷。這種模式一般不建議使用。
3、DCL實現單例
package com.example.imageloader;
public class Singleton {
private static Singleton instance = null;
private Singleton(){};
public static Singleton getInstance(){
if(instance == null){
synchronized (Singleton.class) {
if(instance == null){
instance = new Singleton();
}
}
}
return instance;
}
}
4、靜態內部類
package com.example.imageloader;
public class Singleton {
private Singleton() {
};
public static Singleton getInstance() {
return SingletonHolder.sInstance;
}
/**
* 靜態內部類
*/
private static class SingletonHolder {
private static final Singleton sInstance = new Singleton();
}
}
這是推薦使用的單例模式實現方式
5、使用容器實現單例模式
package com.example.imageloader;
import java.util.HashMap;
import java.util.Map;
public class SingletonManager {
private static Map<String , Object> objMap = new HashMap<String, Object>();
private SingletonManager(){};
public static void registerService(String key,Object instance){
if(!objMap.containsKey(key)){
objMap.put(key, instance);
}
}
public static Object getService(String key){
return objMap.get(key);
}
}