Java反射的小故事

 1 package com.xiaoysec.test;
 2 
 3 public class Person {
 4     private String name;
 5     private String sex;
 6     private int id;
 7 
 8     public String getName() {
 9         return name;
10     }
11 
12     public void setName(String name) {
13         this.name = name;
14     }
15 
16     public String getSex() {
17         return sex;
18     }
19 
20     public void setSex(String sex) {
21         this.sex = sex;
22     }
23 
24     public int getId() {
25         return id;
26     }
27 
28     public void setId(int id) {
29         this.id = id;
30     }
31 
32     public Person(String name, String sex, int id) {
33         this.name = name;
34         this.sex = sex;
35         this.id = id;
36     }
37     private void show(){
38         System.out.println("name is:"+this.name);
39         System.out.println("sex is:"+this.sex);
40         System.out.println("id is:"+this.id);
41     }
42     public static void main(String[] args){
43         System.out.println(args[0]);
44     }
45 }

 1 package com.xiaoysec.test;
 2 
 3 import java.lang.reflect.Constructor;
 4 import java.lang.reflect.Field;
 5 import java.lang.reflect.Method;
 6 
 7 import org.junit.Test;
 8 
 9 public class Classtest {
10     private String simplename;
11 
12     @Test
13     public void test() {
14 
15         try {
16             Class c = Class.forName("com.xiaoysec.test.Person");
17             Constructor constructor = c.getConstructor(new Class[] {
18                     String.class, String.class, int.class });
19             Person p = (Person) constructor.newInstance("xiaoysec", "sex", 19);
20             Method m = c.getDeclaredMethod("show", null); // 获取的是private权限的show方法
21             m.setAccessible(true); // 强行打开访问权限 使用发射可以访问private方法
22                                     // 面试的时候如果被问及private是否可以被访问应该 回答
23                                     // 普通的方式只能在类的内部访问 而通过反射可以访问private
24             m.invoke(p, null);
25             System.out.println(c.getName());
26             System.out.println("-------------");
27             Field f = c.getDeclaredField("name");
28             f.setAccessible(true);
29             Class fieldtype = f.getType();
30             System.out.println(fieldtype);
31             Object o = f.get(p);
32             System.out.println(o.getClass()); // 此处返回的是class java.lang.String
33             System.out.println(o);
34             System.out.println("--------------");
35             Method mainmethod = c.getMethod("main", String[].class); // main方法的反射
36             // mainmethod.invoke(p, new String[]{"xiaoysec"});//argument type
37             // mismatch
38             mainmethod.invoke(p, (Object) new String[] { "xiaoysec" });
39             // mainmethod.invoke(p,new Object[]{new String[]{"xiaoysec"}});
40             // //此方法也是对的
41         } catch (Exception e) {
42             // TODO Auto-generated catch block
43             e.printStackTrace();
44         }
45 
46     }
47 
48 }

 1 package com.xiaoysec.reflecttest;
 2 
 3 import java.lang.reflect.InvocationTargetException;
 4 import java.lang.reflect.Method;
 5 import java.util.ArrayList;
 6 import java.util.Iterator;
 7 
 8 import org.junit.Test;
 9 
10 
11 
12 public class Reflecttest {
13     @Test
14     public void test() {
15         ArrayList<String> list = new ArrayList<String>();
16         list.add("xiaoysec");
17         list.add("B12040423");
18         Iterator it = list.iterator();
19         while (it.hasNext()) {
20             String str = (String) it.next();
21             if (str.equals("xiaoysec")) {
22                 str = "xiaoy";
23                 // list.add("nanjing"); 在iterator作用范围内不能改变集合中的元素
24             }
25             System.out.println(str);
26         }
27 
28     }
29     /**
30      * 下面的測試方法證明了java中的泛型只是针对编译时有效
31      * 通过反射可以绕过泛型的限制
32     */
33     @Test
34     public void test2() {
35         ArrayList<String> list2 = new ArrayList<String>();
36         list2.add("XIAOYSEC");
37         list2.add("12040423");
38         for(String str:list2){
39             System.out.println(str);
40         }
41         System.out.println("-----------------");
42         try {
43             Class c = list2.getClass();
44             Method m = c.getMethod("add", Object.class);  // public boolean add(E e) 
45             m.invoke(list2, 12);  //传入的参数是12 int类型而非String类型
46             Iterator it = list2.iterator();
47             while (it.hasNext()) {
48                 System.out.println(it.next());
49             }
50         } catch (Exception e) {
51             // TODO Auto-generated catch block
52             e.printStackTrace();
53         }
54         
55 
56     }
57 
58 }