Java的反射机制例子

JavaReflection.java

package cn.lee.demo;  
  
import java.lang.reflect.Constructor;  
import java.lang.reflect.Field;  
import java.lang.reflect.InvocationTargetException;  
import java.lang.reflect.Method;  
import java.lang.reflect.Modifier;  
import java.lang.reflect.TypeVariable;  
  
public class Main {  
    /** 
     * 为了看清楚Java反射部分代码，所有异常我都最后抛出来给虚拟机处理！ 
     * @param args 
     * @throws ClassNotFoundException 
     * @throws InstantiationException 
     * @throws IllegalAccessException 
     * @throws InvocationTargetException  
     * @throws IllegalArgumentException  
     * @throws NoSuchFieldException  
     * @throws SecurityException  
     * @throws NoSuchMethodException  
     */  
    public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, SecurityException, NoSuchFieldException, NoSuchMethodException {  
        // TODO Auto-generated method stub  
          
        //Demo1.  通过Java反射机制得到类的包名和类名  
        Demo1();  
        System.out.println("===============================================");  
          
        //Demo2.  验证所有的类都是Class类的实例对象  
        Demo2();  
        System.out.println("===============================================");  
          
        //Demo3.  通过Java反射机制，用Class 创建类对象[这也就是反射存在的意义所在]，无参构造  
        Demo3();  
        System.out.println("===============================================");  
          
        //Demo4:  通过Java反射机制得到一个类的构造函数，并实现构造带参实例对象  
        Demo4();  
        System.out.println("===============================================");  
          
        //Demo5:  通过Java反射机制操作成员变量, set 和 get  
        Demo5();  
        System.out.println("===============================================");  
          
        //Demo6: 通过Java反射机制得到类的一些属性： 继承的接口，父类，函数信息，成员信息，类型等  
        Demo6();  
        System.out.println("===============================================");  
          
        //Demo7: 通过Java反射机制调用类中方法  
        Demo7();  
        System.out.println("===============================================");  
          
        //Demo8: 通过Java反射机制获得类加载器  
        Demo8();  
        System.out.println("===============================================");  
          
    }  
      
    /** 
     * Demo1: 通过Java反射机制得到类的包名和类名 
     */  
    public static void Demo1()  
    {  
        Person person = new Person();  
        System.out.println("Demo1: 包名: " + person.getClass().getPackage().getName() + "，"   
                + "完整类名: " + person.getClass().getName());  
    }  
      
    /** 
     * Demo2: 验证所有的类都是Class类的实例对象 
     * @throws ClassNotFoundException  
     */  
    public static void Demo2() throws ClassNotFoundException  
    {  
        //定义两个类型都未知的Class , 设置初值为null, 看看如何给它们赋值成Person类  
        Class<?> class1 = null;  
        Class<?> class2 = null;  
          
        //写法1, 可能抛出 ClassNotFoundException [多用这个写法]  
        class1 = Class.forName("cn.lee.demo.Person");  
        System.out.println("Demo2:(写法1) 包名: " + class1.getPackage().getName() + "，"   
                + "完整类名: " + class1.getName());  
          
        //写法2  
        class2 = Person.class;  
        System.out.println("Demo2:(写法2) 包名: " + class2.getPackage().getName() + "，"   
                + "完整类名: " + class2.getName());  
    }  
      
    /** 
     * Demo3: 通过Java反射机制，用Class 创建类对象[这也就是反射存在的意义所在] 
     * @throws ClassNotFoundException  
     * @throws IllegalAccessException  
     * @throws InstantiationException  
     */  
    public static void Demo3() throws ClassNotFoundException, InstantiationException, IllegalAccessException  
    {  
        Class<?> class1 = null;  
        class1 = Class.forName("cn.lee.demo.Person");  
        //由于这里不能带参数，所以你要实例化的这个类Person，一定要有无参构造函数哈～  
        Person person = (Person) class1.newInstance();  
        person.setAge(20);  
        person.setName("LeeFeng");  
        System.out.println("Demo3: " + person.getName() + " : " + person.getAge());  
    }  
      
    /** 
     * Demo4: 通过Java反射机制得到一个类的构造函数，并实现创建带参实例对象 
     * @throws ClassNotFoundException  
     * @throws InvocationTargetException  
     * @throws IllegalAccessException  
     * @throws InstantiationException  
     * @throws IllegalArgumentException  
     */  
    public static void Demo4() throws ClassNotFoundException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException  
    {  
        Class<?> class1 = null;  
        Person person1 = null;  
        Person person2 = null;  
          
        class1 = Class.forName("cn.lee.demo.Person");  
        //得到一系列构造函数集合  
        Constructor<?>[] constructors = class1.getConstructors();  
          
        person1 = (Person) constructors[0].newInstance();  
        person1.setAge(30);  
        person1.setName("leeFeng");  
          
        person2 = (Person) constructors[1].newInstance(20,"leeFeng");  
          
        System.out.println("Demo4: " + person1.getName() + " : " + person1.getAge()  
                + "  ,   " + person2.getName() + " : " + person2.getAge()  
                );  
          
    }  
      
    /** 
     * Demo5: 通过Java反射机制操作成员变量, set 和 get 
     *  
     * @throws IllegalAccessException  
     * @throws IllegalArgumentException  
     * @throws NoSuchFieldException  
     * @throws SecurityException  
     * @throws InstantiationException  
     * @throws ClassNotFoundException  
     */  
    public static void Demo5() throws IllegalArgumentException, IllegalAccessException, SecurityException, NoSuchFieldException, InstantiationException, ClassNotFoundException  
    {  
        Class<?> class1 = null;  
        class1 = Class.forName("cn.lee.demo.Person");  
        Object obj = class1.newInstance();  
          
        Field personNameField = class1.getDeclaredField("name");  
        personNameField.setAccessible(true);  
        personNameField.set(obj, "胖虎先森");  
          
          
        System.out.println("Demo5: 修改属性之后得到属性变量的值：" + personNameField.get(obj));  
          
    }  
      
  
    /** 
     * Demo6: 通过Java反射机制得到类的一些属性： 继承的接口，父类，函数信息，成员信息，类型等 
     * @throws ClassNotFoundException  
     */  
    public static void Demo6() throws ClassNotFoundException  
    {  
        Class<?> class1 = null;  
        class1 = Class.forName("cn.lee.demo.SuperMan");  
          
        //取得父类名称  
        Class<?>  superClass = class1.getSuperclass();  
        System.out.println("Demo6:  SuperMan类的父类名: " + superClass.getName());  
          
        System.out.println("===============================================");  
          
          
        Field[] fields = class1.getDeclaredFields();  
        for (int i = 0; i < fields.length; i++) {  
            System.out.println("类中的成员: " + fields[i]);  
        }  
        System.out.println("===============================================");  
          
          
        //取得类方法  
        Method[] methods = class1.getDeclaredMethods();  
        for (int i = 0; i < methods.length; i++) {  
            System.out.println("Demo6,取得SuperMan类的方法：");  
            System.out.println("函数名：" + methods[i].getName());  
            System.out.println("函数返回类型：" + methods[i].getReturnType());  
            System.out.println("函数访问修饰符：" + Modifier.toString(methods[i].getModifiers()));  
            System.out.println("函数代码写法： " + methods[i]);  
        }  
          
        System.out.println("===============================================");  
          
        //取得类实现的接口,因为接口类也属于Class,所以得到接口中的方法也是一样的方法得到哈  
        Class<?> interfaces[] = class1.getInterfaces();  
        for (int i = 0; i < interfaces.length; i++) {  
            System.out.println("实现的接口类名: " + interfaces[i].getName() );  
        }  
          
    }  
      
    /** 
     * Demo7: 通过Java反射机制调用类方法 
     * @throws ClassNotFoundException  
     * @throws NoSuchMethodException  
     * @throws SecurityException  
     * @throws InvocationTargetException  
     * @throws IllegalAccessException  
     * @throws IllegalArgumentException  
     * @throws InstantiationException  
     */  
    public static void Demo7() throws ClassNotFoundException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException, InstantiationException  
    {  
        Class<?> class1 = null;  
        class1 = Class.forName("cn.lee.demo.SuperMan");  
          
        System.out.println("Demo7: \n调用无参方法fly()：");  
        Method method = class1.getMethod("fly");  
        method.invoke(class1.newInstance());  
          
        System.out.println("调用有参方法walk(int m)：");  
        method = class1.getMethod("walk",int.class);  
        method.invoke(class1.newInstance(),100);  
    }  
      
    /** 
     * Demo8: 通过Java反射机制得到类加载器信息 
     *  
     * 在java中有三种类类加载器。[这段资料网上截取] 
 
        1）Bootstrap ClassLoader 此加载器采用c++编写，一般开发中很少见。 
 
        2）Extension ClassLoader 用来进行扩展类的加载，一般对应的是jre\lib\ext目录中的类 
 
        3）AppClassLoader 加载classpath指定的类，是最常用的加载器。同时也是java中默认的加载器。 
     *  
     * @throws ClassNotFoundException  
     */  
    public static void Demo8() throws ClassNotFoundException  
    {  
        Class<?> class1 = null;  
        class1 = Class.forName("cn.lee.demo.SuperMan");  
        String nameString = class1.getClassLoader().getClass().getName();  
          
        System.out.println("Demo8: 类加载器类名: " + nameString);  
    }  
      
      
      
}  
/** 
 *  
 * @author xiaoyaomeng 
 * 
 */  
class  Person{  
    private int age;  
    private String name;  
    public Person(){  
          
    }  
    public Person(int age, String name){  
        this.age = age;  
        this.name = name;  
    }  
  
    public int getAge() {  
        return age;  
    }  
    public void setAge(int age) {  
        this.age = age;  
    }  
    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  
}  
  
class SuperMan extends Person implements ActionInterface  
{  
    private boolean BlueBriefs;  
      
    public void fly()  
    {  
        System.out.println("超人会飞耶～～");  
    }  
      
    public boolean isBlueBriefs() {  
        return BlueBriefs;  
    }  
    public void setBlueBriefs(boolean blueBriefs) {  
        BlueBriefs = blueBriefs;  
    }  
  
    @Override  
    public void walk(int m) {  
        // TODO Auto-generated method stub  
        System.out.println("超人会走耶～～走了" + m + "米就走不动了！");  
    }  
}  
interface ActionInterface{  
    public void walk(int m);  
}