(转)个例子让你了解Java反射机制
原文地址：http://blog.csdn.net/ljphhj/article/details/12858767
JAVA反射机制：
通俗地说,反射机制就是可以把一个类,类的成员(函数,属性),当成一个对象来操作,希望读者能理解,也就是说,类,类的成员,我们在运行的时候还可以动态地去操作他们.
理论的东东太多也没用，下面我们看看实践 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); }
