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 }