Singleton（单例模式）

一、
/**
 * lazy man(不是线程安全的)
 * @author TMAC-J
 *
 */
public class Singleton {
	
	private static Singleton instance;
	
	private Singleton(){}
	
	public static Singleton getInstance(){
		if(instance!=null){
			instance = new Singleton();		
			}
		return instance;
	}
	
}

二、
/**
 * lazy man（线程安全）
 * @author TMAC-J
 *
 */
public class Singleton {
	
	private static Singleton instance;
	
	private Singleton(){}
	
	public static synchronized Singleton getInstance(){
		if(instance!=null){
			instance = new Singleton();		
			}
		return instance;
	}
	
}

三、
/**
 * hungry man（天生线程安全,缺点是类加载的时候就会实例化）
 * @author TMAC-J
 *
 */
public class Singleton {
	
	private static Singleton instance = new Singleton();
	
	private Singleton(){}
	
	public static Singleton getInstance(){
		return instance;
	}
	
}

四、
这种写法和上面效果一样
public class Singleton {  
    private Singleton instance = null;  
    static {  
    instance = new Singleton();  
    }  
    private Singleton (){}  
    public static Singleton getInstance() {  
    return this.instance;  
    }  
}

五、

/**
 * 静态内部类
 * 
 * @author TMAC-J
 *
 */
public class Singleton {
 
	private static class SingletonHolder {
		private static  final Singleton instance = new Singleton();
	}

	private Singleton(){};
	
	public static final Singleton getSinleton(){
		return SingletonHolder.instance;
	}
}

六、

public enum Singleton {  
    INSTANCE;  
}  

七、
/**
 * 双重锁
 * 
 * @author TMAC-J
 *
 */
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;
	}
}


    

最常用的就是双重锁了，效率还可以