1 package jxlPacakge;
 2 
 3 public class Object_num {
 4      public static void main(String[] args) {
 5             // TODO Auto-generated method stub
 6        Roo obj1=new Roo();
 7        Roo obj2=new Roo();
 8        Roo obj3=null;
 9        System.out.println("定义了"+Roo.num+"个对象。");
10         }
11 
12     }
13     class Roo{
14         static int num=0;
15          Roo(){
16             number();
17         }
18          static void number(){
19              num++;
20          }
21 }