设计模式之单例模式

单例模式1

public class A{   
    
	   private static A a = null;   
	      
	   private  A(){   
	}   
	      
	   public static A getA(){   
	       
	     if(a == null){   
	       a = new A();   
	   }   
	    return a;   
	}   
	      
	}