java面试题三

饿汉式:
public class SingletonDemo{
	//创建一个静态类对象    
	private static SingletonDemo instance = new SingletonDemo(); 
	//修饰符限定为private,避免了类在外部被实例化   
    private SingletonDemo(){
	}  
	public static SingletonDemo getInstance(){
		return instance;
	}
}

懒汉式:
public class SingletonDemo{  
	private static SingletonDemo instance = null;  
	private SingletonDemo(){
	}
	public static synchronized SingletonDemo getInstance(){
		if(instance == null){
			instance = new SingletonDemo();
		}
		return instance;
	}
}