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