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

巴特西

复习java基础第七天（反射）

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