Java总结篇系列：Java 反射
Java反射：
1 package com.corn;2
3 import java.lang.reflect.Constructor;
4 import java.lang.reflect.Field;
5 import java.lang.reflect.InvocationTargetException;
6 import java.lang.reflect.Method;
7
8 public class TestReflect {
9
10 public static void main(String[] args) {
11
12 // 获取“类类型对象” 方法1
13 Class<?> c0 = User.class;
14
15 // 获取“类类型对象” 方法2
16 User user1 = new User();
17 Class<?> c1 = user1.getClass();
18
19 User user2 = new User();
20 Class<?> c2 = user2.getClass();
21
22 System.out.println("user class instance 0:" + c0); //user class instance 0:class com.corn.User
23 System.out.println("user class instance 1:" + c1); //user class instance 1:class com.corn.User
24 System.out.println("user class instance 2:" + c2); //user class instance 2:class com.corn.User
25
26 //c0 == c1 :true, c1 == c2 :true
27 System.out.println("c0 == c1 :" + (c0 == c1) + ", c1 == c2 :" + (c1 == c2));
28
29 try {
30 // 获取“类类型对象” 方法3
31 Class<?> c3 = Class.forName("com.corn.User");
32 System.out.println("user class c3:" + c3); //user class c3:class com.corn.User
33
34 try {
35 User user3 = (User) c3.newInstance();
36
37 //Constructor public com.corn.User(int,java.lang.String,int)
38 //Constructor public com.corn.User(int,java.lang.String)
39 //Constructor public com.corn.User()
40 Constructor<?>[] cons = c3.getConstructors();
41 for (int i = 0; i < cons.length; i++) {
42 // 一次返回类定义中所有public修饰符修饰的“构造器对象”,其与类定义中的构造器顺序不一定相同
43 System.out.println("Constructor " + cons[i]);
44 }
45
46 try {
47 User user4 = (User) cons[1].newInstance(51, "corn");
48 //user instance 4:user instance uid:51 name:corn
49 System.out.println("user instance 4:" + user4);
50
51 // 返回特定参数类型的“构造器对象”所新建的实例
52 User user40;
53 user40 = (User) c3.getConstructor(int.class, String.class).newInstance(520, "corn0");
54 //user instance 40:user instance uid:520 name:corn0
55 System.out.println("user instance 40:" + user40);
56
57 // 返回该类“类类型对象”的所有的父类“类类型对象”
58 Class<?> father = c3.getSuperclass();
59 //father class instance class com.corn.Person
60 System.out.println("father class instance " + father);
61
62 //返回类对象所有的接口对象（其实也是类类型对象）数组
63 Class<?>[] interfaceArray = c3.getInterfaces();
64 //interface class instance 0 interface com.corn.Workable
65 //interface class instance 1 interface com.corn.Thinkable
66 for (int i = 0; i < interfaceArray.length; i++) {
67 // 与implements中接口顺序相同
68 System.out.println("interface class instance " + i + " " + interfaceArray[i]);
69 }
70
71 } catch (IllegalArgumentException e) {
72 e.printStackTrace();
73 } catch (InvocationTargetException e) {
74 e.printStackTrace();
75 }
76
77 } catch (InstantiationException e) {
78 e.printStackTrace();
79 } catch (IllegalAccessException e) {
80 e.printStackTrace();
81 }
82 } catch (ClassNotFoundException e) {
83 e.printStackTrace();
84 } catch (Exception e) {
85 e.printStackTrace();
86 }
87
88 // 返回“类类型对象”所具有的全部属性实例/对象
89 Field[] fieldArray = c0.getDeclaredFields();
90 //filed 0 private int com.corn.User.uid
91 //filed 1 private java.lang.String com.corn.User.name
92 //filed 2 private int com.corn.User.age
93 for (int i = 0; i < fieldArray.length; i++) {
94 System.out.println("filed " + i + " " + fieldArray[i]);
95 }
96
97 User u = new User(12, "yumidi", 99);
98
99 try {
100 // 直接获取private/私有属性的值
101 Field nameField = c0.getDeclaredField("name");
102 //取消Java对访问修饰符的检查
103 nameField.setAccessible(true);
104 String nameValue = (String) nameField.get(u);
105 //name:yumidi
106 System.out.println("name:" + nameValue);
107
108 // 直接改变private/私有属性的值
109 nameField.set(u, "corn");
110 //new name:corn
111 System.out.println("new name:" + u.getName());
112
113 } catch (NoSuchFieldException e) {
114 e.printStackTrace();
115 } catch (SecurityException e) {
116 e.printStackTrace();
117 } catch (Exception e) {
118 e.printStackTrace();
119 }
120
121 //访问私有方法
122 try {
123 Method method = c0.getDeclaredMethod("getResult");
124 //取消Java对访问修饰符的检查
125 method.setAccessible(true);
126 int result = (int) method.invoke(u);
127 //result:1000
128 System.out.println("result:" + result);
129
130 } catch (NoSuchMethodException e) {
131 e.printStackTrace();
132 } catch (SecurityException e) {
133 e.printStackTrace();
134 } catch (Exception e) {
135 e.printStackTrace();
136 }
137
138 }
139 }
140
141 class User extends Person implements Workable, Thinkable {
142
143 private int uid;
144 private String name;
145 private int age;
146
147 public User() {
148
149 }
150
151 private User(int uid) {
152 this.uid = uid;
153 }
154
155 protected User(String name) {
156 this.name = name;
157 }
158
159 public User(int uid, String name) {
160 this.uid = uid;
161 this.name = name;
162 }
163
164 public User(int uid, String name, int age) {
165 this.uid = uid;
166 this.name = name;
167 this.age = age;
168 }
169
170 public int getUid() {
171 return uid;
172 }
173
174 public void setUid(int uid) {
175 this.uid = uid;
176 }
177
178 public String getName() {
179 return name;
180 }
181
182 public void setName(String name) {
183 this.name = name;
184 }
185
186 public int getAge() {
187 return age;
188 }
189
190 public void setAge(int age) {
191 this.age = age;
192 }
193
194 private int getResult() {
195 return 1000;
196 }
197
198 @Override
199 public String toString() {
200 return "user instance uid:" + this.uid + " name:" + this.name;
201 }
202
203 }
204
205 class Person {
206
207 }
208
209 interface Workable {
210
211 }
212
213 interface Thinkable {
214
215 }
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