Java总结篇系列：Java 反射

Java反射：

 package com.corn;

 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;

 public class TestReflect {

     public static void main(String[] args) {

         // 获取“类类型对象”  方法1
         Class<?> c0 = User.class;

         // 获取“类类型对象”  方法2
         User user1 = new User();
         Class<?> c1 = user1.getClass();

         User user2 = new User();
         Class<?> c2 = user2.getClass();

         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

         //c0 == c1 :true, c1 == c2 :true
         System.out.println("c0 == c1 :" + (c0 == c1) + ", c1 == c2 :" + (c1 == c2));

         try {
             // 获取“类类型对象”  方法3
             Class<?> c3 = Class.forName("com.corn.User");
             System.out.println("user class c3:" + c3); //user class c3:class com.corn.User

             try {
                 User user3 = (User) c3.newInstance();

                 //Constructor public com.corn.User(int,java.lang.String,int)
                 //Constructor public com.corn.User(int,java.lang.String)
                 //Constructor public com.corn.User()
                 Constructor<?>[] cons = c3.getConstructors();
                 for (int i = 0; i < cons.length; i++) {
                     // 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]);
                 }

                 try {
                     User user4 = (User) cons[1].newInstance(51, "corn");
                     //user instance 4:user instance uid:51 name:corn
                     System.out.println("user instance 4:" + user4);

                     // 返回特定参数类型的“构造器对象”所新建的实例
                     User user40;
                     user40 = (User) c3.getConstructor(int.class, String.class).newInstance(520, "corn0");
                     //user instance 40:user instance uid:520 name:corn0
                     System.out.println("user instance 40:" + user40);

                     // 返回该类“类类型对象”的所有的父类“类类型对象”
                     Class<?> father = c3.getSuperclass();
                     //father class instance class com.corn.Person
                     System.out.println("father class instance " + father);

                     //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();
                     //interface class instance 0 interface com.corn.Workable
                     //interface class instance 1 interface com.corn.Thinkable
                     for (int i = 0; i < interfaceArray.length; i++) {
                         // 与implements中接口顺序相同
                         System.out.println("interface class instance " + i + " " + interfaceArray[i]);
                     }

                 } catch (IllegalArgumentException e) {
                     e.printStackTrace();
                 } catch (InvocationTargetException e) {
                     e.printStackTrace();
                 }

             } catch (InstantiationException e) {
                 e.printStackTrace();
             } catch (IllegalAccessException e) {
                 e.printStackTrace();
             }
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (Exception e) {
             e.printStackTrace();
         }

         // 返回“类类型对象”所具有的全部属性实例/对象
         Field[] fieldArray = c0.getDeclaredFields();
         //filed 0 private int com.corn.User.uid
         //filed 1 private java.lang.String com.corn.User.name
         //filed 2 private int com.corn.User.age
         for (int i = 0; i < fieldArray.length; i++) {
             System.out.println("filed " + i + " " + fieldArray[i]);
         }

         User u = new User(12, "yumidi", 99);

         try {
             // 直接获取private/私有属性的值
             Field nameField = c0.getDeclaredField("name");
             //取消Java对访问修饰符的检查
             nameField.setAccessible(true);
             String nameValue = (String) nameField.get(u);
             //name:yumidi
             System.out.println("name:" + nameValue);

             // 直接改变private/私有属性的值
             nameField.set(u, "corn");
             //new name:corn
             System.out.println("new name:" + u.getName());

         } catch (NoSuchFieldException e) {
             e.printStackTrace();
         } catch (SecurityException e) {
             e.printStackTrace();
         } catch (Exception e) {
             e.printStackTrace();
         }

         //访问私有方法
         try {
             Method method = c0.getDeclaredMethod("getResult");
             //取消Java对访问修饰符的检查
             method.setAccessible(true);
             int result = (int) method.invoke(u);
             //result:1000
             System.out.println("result:" + result);

         } catch (NoSuchMethodException e) {
             e.printStackTrace();
         } catch (SecurityException e) {
             e.printStackTrace();
         } catch (Exception e) {
             e.printStackTrace();
         }

     }
 }

 class User extends Person implements Workable, Thinkable {

     private int uid;
     private String name;
     private int age;

     public User() {

     }

     private User(int uid) {
         this.uid = uid;
     }

     protected User(String name) {
         this.name = name;
     }

     public User(int uid, String name) {
         this.uid = uid;
         this.name = name;
     }

     public User(int uid, String name, int age) {
         this.uid = uid;
         this.name = name;
         this.age = age;
     }

     public int getUid() {
         return uid;
     }

     public void setUid(int uid) {
         this.uid = uid;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public int getAge() {
         return age;
     }

     public void setAge(int age) {
         this.age = age;
     }

     private int getResult() {
         return 1000;
     }

     @Override
     public String toString() {
         return "user instance uid:" + this.uid + " name:" + this.name;
     }

 }

 class Person {

 }

 interface Workable {

 }

 interface Thinkable {

 }