Java中static用来计数

搓搓的代码
 1 import java.util.ArrayList;
 2 import java.util.Iterator;
 3 class Student{
 4     private static int num;
 5     private String name;
 6     private int age;
 7     private int number;
 8     public Student(){}
 9     public Student(String name,int age) {
10         num++;
11         this.number=num;
12         this.name=name;
13         this.age=age;
14     }
15     public void setName(String name) {
16         this.name=name;
17     }
18     public String getName() {
19         return name;
20     }
21     public void setAge(int age) {
22         this.age=age;
23     }
24     public int getAge() {
25         return age;
26     }
27     public int getNumber() {
28         return number;
29     }
30 }
31 public class Main{
32     public static void main(String[] args) {
33         Student[] arr=new Student[5];
34         arr[0]=new Student("张三",19);
35         arr[1]=new Student("李四",18);
36         arr[2]=new Student("王五",18);
37         for(int i=0;i<3;i++) {
38             System.out.println(arr[i].getName()+" "+arr[i].getAge()+" "+arr[i].getNumber());
39         }
40         /*
41         ArrayList<String> t =new ArrayList<String>();
42         t.add("abc");
43         t.add("1551");
44         Iterator<String> it = t.iterator();
45         while(it.hasNext()) {
46              Object obj=it.next();
47              System.out.println(obj);
48          }
49         */
50         /*
51         ArrayList list = new ArrayList();
52         list.add("str");
53         list.add(123);
54         Iterator it =list.iterator();
55         while(it.hasNext()) {
56             Object obj=it.next();
57             System.out.println(obj);
58         }
59         */
60         
61         
62     }
63 }