复习java基础第七天（反射）

一：目标

Ø理解 Class 类

Ø理解 Java 的类加载机制

Ø学会使用 ClassLoader 进行类加载

Ø理解反射的机制

Ø掌握 Constructor、Method、Field 类的用法

Ø理解并掌握动态代理

 

1、Class类

–对象照镜子后可以得到的信息：某个类的数据成员名、方法和构造器、某个类到底实现了哪些接口。

对于每个类而言，JRE 都为其保留一个不变的 Class 类型的对象。

一个 Class 对象包含了特定某个类的有关信息。

–  Class 对象只能由系统建立对象。

–  一个类在 JVM 中只会有一个Class实例。

–  每个类的实例都会记得自己是由哪个 Class 实例所生成 。

获取 Class 对象的方式：

 

 

Class类的常用方法：

 

三种类加载器（ClassLoader):

 

练习代码:

 package com.shellway.test;

 public class Person {
     String name;
     String age;

     public String getName() {
         return name;
     }

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

     public String getAge() {
         return age;
     }

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

     public Person(String name, String age) {
         super();
         this.name = name;
         this.age = age;
         System.out.println("有参数的构造器。。。。");
     }

     public Person() {
         System.out.println("无参数的构造器。。。。");
     }
 }

Person类

 package com.shellway.test;

 import static org.junit.Assert.*;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.InputStream;
 import java.lang.reflect.Field;
 import org.junit.Test;

 public class ReflectionTest {
     @Test
     public void testClassLoader() throws ClassNotFoundException,
             FileNotFoundException {
         ClassLoader classLoader = ClassLoader.getSystemClassLoader();
         System.out.println(classLoader);
         classLoader = classLoader.getParent();
         System.out.println(classLoader);
         classLoader = classLoader.getParent();
         System.out.println(classLoader);

         // 测试由哪个类加载器进行加载
         classLoader = Class.forName("com.shellway.test.Person")
                 .getClassLoader();
         System.out.println(classLoader);

         // 调用getResourceAsStream获取类路径下文件对应的输入流
         InputStream in = null;
         in = this.getClass().getClassLoader()
                 .getResourceAsStream("com/shellway/test/test.properties");
         // new FileInputStream("com/shellway/test/test.properties");
         System.out.println(in);
     }

     @Test
     public void testNewInstance() throws ClassNotFoundException,
             InstantiationException, IllegalAccessException {
         String className = "com.shellway.test.Person";
         Class clazz = Class.forName(className);
         Object obj = clazz.newInstance();// 实际上调用的是无参数的构造器创建的实例。
         System.out.println(obj);
     }

     @Test
     public void test() throws ClassNotFoundException {
         // 1.得到Class对象的三种方法
         // 1.1直接通过类名.class的方式得到
         Class clazz = null;
         clazz = Person.class;
         Field[] fields = clazz.getDeclaredFields();
         System.out.println(clazz);

         // 2.1通过对象调用getClass()方法来获取
         Person person = new Person();// Object obj =new Person();
         clazz = person.getClass(); // clazz = obj.getClass();

         // 3.1通过全类名的方式获取,用的最多的
         String className = "com.shellway.test.Person";
         clazz = Class.forName(className);
     }
 }

ReflectionTest类

 利用反射写一个晚会案例：

 Singing=com.shellway.Reflection.impl.Liudehua
 Dancing=com.shellway.Reflection.impl.Guofucheng
 Xiangsheng=com.shellway.Reflection.impl.Guodegang

party.properties

 package com.shellway.Reflection;

 import com.shellway.Reflection.imp.Dancing;
 import com.shellway.Reflection.imp.Singing;
 import com.shellway.Reflection.imp.Xiangsheng;

 public class EveningParty {
     public static void main(String[] args) throws Exception {
         System.out.println("晚会开始!!!!!");
         //唱歌
         Singing sing = Factory.getSinger();
         sing.singing();
         //跳舞
         Dancing dancing = Factory.getDancer();
         dancing.dancing();
         //相声
         Xiangsheng xiangsheng = Factory.getPerformer();
         xiangsheng.show();
         System.out.println("晚会结束!!!!!");
     }
 }

EveningParty.java

 package com.shellway.Reflection.imp;

 public interface Singing {
     public void singing();
 }

Singing 接口

 package com.shellway.Reflection.imp;

 public interface Dancing {
     void dancing();
 }

Dancing 接口

 package com.shellway.Reflection.imp;

 public interface Xiangsheng {
      void show();
 }

Xiangsheng 接口

接口实现类：

 package com.shellway.Reflection.impl;

 import com.shellway.Reflection.imp.Singing;

 public class Liudehua implements Singing {

     @Override
     public void singing() {
         System.out.println("刘德华演唱：中国人");
     }
 }

歌手刘德华

 package com.shellway.Reflection.impl;

 import com.shellway.Reflection.imp.Singing;

 public class Xietingfeng implements Singing {

     @Override
     public void singing() {
         System.out.println("谢霆锋演唱:因为爱所以爱...");
     }
 }

歌手谢霆锋

 package com.shellway.Reflection.impl;

 import com.shellway.Reflection.imp.Dancing;

 public class Yangliping implements Dancing {

     @Override
     public void dancing() {
         System.out.println("杨丽萍表演孔雀舞...");
     }
 }

舞者杨丽萍

 package com.shellway.Reflection.impl;

 import com.shellway.Reflection.imp.Dancing;

 public class Guofucheng implements Dancing {

     @Override
     public void dancing() {
         System.out.println("郭富城跳广场舞...");
     }
 }

舞者郭富城

 package com.shellway.Reflection.impl;

 import com.shellway.Reflection.imp.Xiangsheng;

 public class Guodegang implements Xiangsheng {

     @Override
     public void show() {
         System.out.println("郭德纲表演相声...");
     }
 }

相声演员郭德纲

工厂类与配置文件结合实现反射

 package com.shellway.Reflection;

 import java.util.ResourceBundle;

 import com.shellway.Reflection.imp.Dancing;
 import com.shellway.Reflection.imp.Singing;
 import com.shellway.Reflection.imp.Xiangsheng;

 public class Factory {

     public static Singing getSinger() throws Exception{
         String pathName = ResourceBundle.getBundle("party").getString("Singing");
         Object obj = Class.forName(pathName).newInstance();
         return  (Singing) obj;
     }
     public static Dancing getDancer() throws Exception{
         String pathName = ResourceBundle.getBundle("party").getString("Dancing");
         Object obj = Class.forName(pathName).newInstance();
         return (Dancing) obj;
     }

     public static Xiangsheng getPerformer() throws Exception{
         String pathName = ResourceBundle.getBundle("party").getString("Xiangsheng");
         Object obj = Class.forName(pathName).newInstance();
         return (Xiangsheng) obj;
     }

 }

Factory