参数可以在子方法中赋值，主方法中得到

 1 import java.util.*;
 2 
 3 public class Test {
 4     public static void main(String[] args) {
 5         
 6         Person person = new Person();
 7         int a = 100;
 8         int b = person.doPerson(a);
 9         System.out.println(b);
10         List<String> list = new ArrayList<String>();
11         person.doList(list);
12         System.out.println(list.size());
13         System.out.println(list.get(0));
14         System.out.println(list.get(1));
15     }
16 }
17 
18 class Person {
19     public int doPerson(int c) {
20         c = 50;
21         return c;
22     }
23     
24     public void doList(List<String> list) {
25         list.add("hello");
26         list.add("world");
27     }
28 }