Java总结篇系列：Java 反射

Java反射：

 

package com.corn;  2 
import java.lang.reflect.Constructor;  4 import java.lang.reflect.Field;  5 import java.lang.reflect.InvocationTargetException;  6 import java.lang.reflect.Method;  7 
public class TestReflect {  9 
    public static void main(String[] args) {  11 
        // 获取“类类型对象” 方法1
        Class<?> c0 = User.class;  14 
        // 获取“类类型对象” 方法2
        User user1 = new User();  17         Class<?> c1 = user1.getClass();  18 
        User user2 = new User();  20         Class<?> c2 = user2.getClass();  21 
        System.out.println("user class instance 0:" + c0); //user class instance 0:class com.corn.User
        System.out.println("user class instance 1:" + c1); //user class instance 1:class com.corn.User
        System.out.println("user class instance 2:" + c2); //user class instance 2:class com.corn.User  25 
        //c0 == c1 :true, c1 == c2 :true
        System.out.println("c0 == c1 :" + (c0 == c1) + ", c1 == c2 :" + (c1 == c2));  28 
        try {  30             // 获取“类类型对象” 方法3
            Class<?> c3 = Class.forName("com.corn.User");  32             System.out.println("user class c3:" + c3); //user class c3:class com.corn.User

            try {  35                 User user3 = (User) c3.newInstance();  36 
                //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()
                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
                    System.out.println("Constructor " + cons[i]);  44  }  45 
                try {  47                     User user4 = (User) cons[1].newInstance(51, "corn");  48                     //user instance 4:user instance uid:51 name:corn
                    System.out.println("user instance 4:" + user4);  50 
                    // 返回特定参数类型的“构造器对象”所新建的实例
 User user40;  53                     user40 = (User) c3.getConstructor(int.class, String.class).newInstance(520, "corn0");  54                     //user instance 40:user instance uid:520 name:corn0
                    System.out.println("user instance 40:" + user40);  56 
                    // 返回该类“类类型对象”的所有的父类“类类型对象”
                    Class<?> father = c3.getSuperclass();  59                     //father class instance class com.corn.Person
                    System.out.println("father class instance " + father);  61 
                    //返回类对象所有的接口对象（其实也是类类型对象）数组
                    Class<?>[] interfaceArray = c3.getInterfaces();  64                     //interface class instance 0 interface com.corn.Workable  65                     //interface class instance 1 interface com.corn.Thinkable
                    for (int i = 0; i < interfaceArray.length; i++) {  67                         // 与implements中接口顺序相同
                        System.out.println("interface class instance " + i + " " + interfaceArray[i]);  69  }  70 
                } catch (IllegalArgumentException e) {  72  e.printStackTrace();  73                 } catch (InvocationTargetException e) {  74  e.printStackTrace();  75  }  76 
            } 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 
        // 返回“类类型对象”所具有的全部属性实例/对象
        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
        for (int i = 0; i < fieldArray.length; i++) {  94             System.out.println("filed " + i + " " + fieldArray[i]);  95  }  96 
        User u = new User(12, "yumidi", 99);  98 
        try { 100             // 直接获取private/私有属性的值
            Field nameField = c0.getDeclaredField("name"); 102             //取消Java对访问修饰符的检查 
            nameField.setAccessible(true); 104             String nameValue = (String) nameField.get(u); 105             //name:yumidi
            System.out.println("name:" + nameValue); 107 
            // 直接改变private/私有属性的值
            nameField.set(u, "corn"); 110             //new name:corn
            System.out.println("new name:" + u.getName()); 112 
        } catch (NoSuchFieldException e) { 114  e.printStackTrace(); 115         } catch (SecurityException e) { 116  e.printStackTrace(); 117         } catch (Exception e) { 118  e.printStackTrace(); 119  } 120 
        //访问私有方法
        try { 123             Method method = c0.getDeclaredMethod("getResult"); 124             //取消Java对访问修饰符的检查
            method.setAccessible(true); 126             int result = (int) method.invoke(u); 127             //result:1000
            System.out.println("result:" + result); 129 
        } catch (NoSuchMethodException e) { 131  e.printStackTrace(); 132         } catch (SecurityException e) { 133  e.printStackTrace(); 134         } catch (Exception e) { 135  e.printStackTrace(); 136  } 137 
 } 139 } 140 
class User extends Person implements Workable, Thinkable { 142 
    private int uid; 144     private String name; 145     private int age; 146 
    public User() { 148 
 } 150 
    private User(int uid) { 152         this.uid = uid; 153  } 154 
    protected User(String name) { 156         this.name = name; 157  } 158 
    public User(int uid, String name) { 160         this.uid = uid; 161         this.name = name; 162  } 163 
    public User(int uid, String name, int age) { 165         this.uid = uid; 166         this.name = name; 167         this.age = age; 168  } 169 
    public int getUid() { 171         return uid; 172  } 173 
    public void setUid(int uid) { 175         this.uid = uid; 176  } 177 
    public String getName() { 179         return name; 180  } 181 
    public void setName(String name) { 183         this.name = name; 184  } 185 
    public int getAge() { 187         return age; 188  } 189 
    public void setAge(int age) { 191         this.age = age; 192  } 193 
    private int getResult() { 195         return 1000; 196  } 197 
 @Override 199     public String toString() { 200         return "user instance uid:" + this.uid + " name:" + this.name; 201  } 202 
} 204 
class Person { 206 
} 208 
interface Workable { 210 
} 212 
interface Thinkable { 214 
}