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。。。。");
    }
}

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);
    }
}

 

 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

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!!!!!");
    }
}

package com.shellway.Reflection.imp;

public interface Singing {
    public void singing();
}

package com.shellway.Reflection.imp;

public interface Dancing {
    void dancing();
}

package com.shellway.Reflection.imp;

public interface Xiangsheng {
     void show();
}

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");
    }
}

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...");
    }
}

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...");
    }
}

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...");
    }
}

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...");
    }
}

 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;
    }
        
}