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:

 1 package com.shellway.test;
 2 
 3 public class Person {
 4     String name;
 5     String age;
 6 
 7     public String getName() {
 8         return name;
 9     }
10 
11     public void setName(String name) {
12         this.name = name;
13     }
14 
15     public String getAge() {
16         return age;
17     }
18 
19     public void setAge(String age) {
20         this.age = age;
21     }
22 
23     public Person(String name, String age) {
24         super();
25         this.name = name;
26         this.age = age;
27         System.out.println("有参数的构造器。。。。");
28     }
29 
30     public Person() {
31         System.out.println("无参数的构造器。。。。");
32     }
33 }

Person类

 1 package com.shellway.test;
 2 
 3 import static org.junit.Assert.*;
 4 import java.io.FileInputStream;
 5 import java.io.FileNotFoundException;
 6 import java.io.InputStream;
 7 import java.lang.reflect.Field;
 8 import org.junit.Test;
 9 
10 public class ReflectionTest {
11     @Test
12     public void testClassLoader() throws ClassNotFoundException,
13             FileNotFoundException {
14         ClassLoader classLoader = ClassLoader.getSystemClassLoader();
15         System.out.println(classLoader);
16         classLoader = classLoader.getParent();
17         System.out.println(classLoader);
18         classLoader = classLoader.getParent();
19         System.out.println(classLoader);
20 
21         // 测试由哪个类加载器进行加载
22         classLoader = Class.forName("com.shellway.test.Person")
23                 .getClassLoader();
24         System.out.println(classLoader);
25 
26         // 调用getResourceAsStream获取类路径下文件对应的输入流
27         InputStream in = null;
28         in = this.getClass().getClassLoader()
29                 .getResourceAsStream("com/shellway/test/test.properties");
30         // new FileInputStream("com/shellway/test/test.properties");
31         System.out.println(in);
32     }
33 
34     @Test
35     public void testNewInstance() throws ClassNotFoundException,
36             InstantiationException, IllegalAccessException {
37         String className = "com.shellway.test.Person";
38         Class clazz = Class.forName(className);
39         Object obj = clazz.newInstance();// 实际上调用的是无参数的构造器创建的实例。
40         System.out.println(obj);
41     }
42 
43     @Test
44     public void test() throws ClassNotFoundException {
45         // 1.得到Class对象的三种方法
46         // 1.1直接通过类名.class的方式得到
47         Class clazz = null;
48         clazz = Person.class;
49         Field[] fields = clazz.getDeclaredFields();
50         System.out.println(clazz);
51 
52         // 2.1通过对象调用getClass()方法来获取
53         Person person = new Person();// Object obj =new Person();
54         clazz = person.getClass(); // clazz = obj.getClass();
55 
56         // 3.1通过全类名的方式获取,用的最多的
57         String className = "com.shellway.test.Person";
58         clazz = Class.forName(className);
59     }
60 }

ReflectionTest类

利用反射写一个晚会案例：

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

party.properties

 1 package com.shellway.Reflection;
 2 
 3 import com.shellway.Reflection.imp.Dancing;
 4 import com.shellway.Reflection.imp.Singing;
 5 import com.shellway.Reflection.imp.Xiangsheng;
 6 
 7 public class EveningParty {
 8     public static void main(String[] args) throws Exception {
 9         System.out.println("晚会开始!!!!!");
10         //唱歌
11         Singing sing = Factory.getSinger();
12         sing.singing();
13         //跳舞
14         Dancing dancing = Factory.getDancer();
15         dancing.dancing();
16         //相声
17         Xiangsheng xiangsheng = Factory.getPerformer();
18         xiangsheng.show();
19         System.out.println("晚会结束!!!!!");
20     }
21 }

EveningParty.java

1 package com.shellway.Reflection.imp;
2 
3 public interface Singing {
4     public void singing();
5 }

Singing 接口

1 package com.shellway.Reflection.imp;
2 
3 public interface Dancing {
4     void dancing();
5 }

Dancing 接口

1 package com.shellway.Reflection.imp;
2 
3 public interface Xiangsheng {
4      void show();
5 }

Xiangsheng 接口

接口实现类：

 1 package com.shellway.Reflection.impl;
 2 
 3 import com.shellway.Reflection.imp.Singing;
 4 
 5 public class Liudehua implements Singing {
 6 
 7     @Override
 8     public void singing() {
 9         System.out.println("刘德华演唱：中国人");
10     }
11 }

歌手刘德华

 1 package com.shellway.Reflection.impl;
 2 
 3 import com.shellway.Reflection.imp.Singing;
 4 
 5 public class Xietingfeng implements Singing {
 6 
 7     @Override
 8     public void singing() {
 9         System.out.println("谢霆锋演唱:因为爱所以爱...");
10     }
11 }

歌手谢霆锋

 1 package com.shellway.Reflection.impl;
 2 
 3 import com.shellway.Reflection.imp.Dancing;
 4 
 5 public class Yangliping implements Dancing {
 6 
 7     @Override
 8     public void dancing() {
 9         System.out.println("杨丽萍表演孔雀舞...");
10     }
11 }

舞者杨丽萍

 1 package com.shellway.Reflection.impl;
 2 
 3 import com.shellway.Reflection.imp.Dancing;
 4 
 5 public class Guofucheng implements Dancing {
 6 
 7     @Override
 8     public void dancing() {
 9         System.out.println("郭富城跳广场舞...");
10     }
11 }

舞者郭富城

 1 package com.shellway.Reflection.impl;
 2 
 3 import com.shellway.Reflection.imp.Xiangsheng;
 4 
 5 public class Guodegang implements Xiangsheng {
 6 
 7     @Override
 8     public void show() {
 9         System.out.println("郭德纲表演相声...");
10     }
11 }

相声演员郭德纲

工厂类与配置文件结合实现反射

 1 package com.shellway.Reflection;
 2 
 3 import java.util.ResourceBundle;
 4 
 5 import com.shellway.Reflection.imp.Dancing;
 6 import com.shellway.Reflection.imp.Singing;
 7 import com.shellway.Reflection.imp.Xiangsheng;
 8 
 9 public class Factory {
10 
11     public static Singing getSinger() throws Exception{
12         String pathName = ResourceBundle.getBundle("party").getString("Singing");
13         Object obj = Class.forName(pathName).newInstance();
14         return  (Singing) obj;
15     }
16     public static Dancing getDancer() throws Exception{
17         String pathName = ResourceBundle.getBundle("party").getString("Dancing");
18         Object obj = Class.forName(pathName).newInstance();
19         return (Dancing) obj;
20     }
21 
22     public static Xiangsheng getPerformer() throws Exception{
23         String pathName = ResourceBundle.getBundle("party").getString("Xiangsheng");
24         Object obj = Class.forName(pathName).newInstance();
25         return (Xiangsheng) obj;
26     }
27         
28 }

Factory