使用类的静态字段和构造函数，可以跟踪某个类所创建对象的个数

package ke2;

public class Genzong {
    private static int n = 0;
    public Genzong() {
        n++;
    }
    public static int GetNum() {
        return n;
    }
    public static void main(String[] args) {
        Genzong n1=new Genzong();
        Genzong n2=new Genzong();
        Genzong n3=new Genzong();
        Genzong n4=new Genzong();
        Genzong n5=new Genzong();
        Genzong n6=new Genzong();
        System.out.println("已生成对象个数："+Genzong.GetNum());
    }
}