建立一個靜態變數，每生成一個物件，使該變數加一

package trackobjectnum;

public class ObjectNum {
    private static int n = 0;
    public ObjectNum() {
        n = n + 1;
    }
    public static int getNum() {
        return n;
    }
    
    public static void main(String[] args) {
        ObjectNum o1 = new ObjectNum();
        ObjectNum o2 
 
= new ObjectNum();
        ObjectNum o3 = new ObjectNum();
        ObjectNum o4 = new ObjectNum();
        System.out.println("已生成物件個數為：" + ObjectNum.getNum());
    }
}

執行結果