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 }