简单原理介绍java反射（2）

public class Person {private String name;private int age;public Person(String name,int age) {super();this.name = name;this.age = age;}public   Person(){}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Person [name=" + name + ", age=" + age + "]";}public void show(){System.out.println("show");}public void fun(String str){System.out.println(str);}public static void function(){System.out.println("static");}}

public class Demo1 {/** * 反射：动态获取字节码文件对象(Person.class)，并对其成员进行运行 *  * 动态获取字节码文件对象的方式： * 1：任何一个对象都是由字节码文件对象创建的，所以任何一个对象都可以得到自己的字节码文件对象 *   那么这个功能应该定义在Object中，所以使用 getClass() *   需要先new对象 *    * 2:每种数据类型都有一个 静态的class 属性,通过该属性可以得到字节码文件对象 *   不需要new对象，但是需要Person类存在 *    * 3:Class类提供了一个静态的forName(String str)方法  *   只需要提供字符串形式的包名+类名 * @throws ClassNotFoundException  */public static void main(String[] args) throws ClassNotFoundException {          getClaz();          getClaz2();          getClaz3();}//Class类提供了一个静态的forNamepublic static void getClaz3() throws ClassNotFoundException{Class<?> claz1 = Class.forName("com.qianfeng.reflect.Person");Class<?> claz2 = Class.forName("com.qianfeng.reflect.Person");System.out.println(claz1==claz2);}//通过静态属性class获取字节码文件对象public static void getClaz2(){Class<Person> claz1 = Person.class;Class<Person> claz2 = Person.class;System.out.println(claz1==claz2);}//1:使用Object中的 getClass()获取字节码文件对象public static void getClaz(){//Person person1 = new Person();//先加载Person.class到方法区//Class<? extends Person> claz1 = person1.getClass();//得到了 Person.class////Person person2 = new Person();//Class<? extends Person> claz2 = person2.getClass();//得到了 Person.class////System.out.println(claz1==claz2);//true}}

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;public class Demo2 {/** * 动态获取字节码文件对象，并创建对象 * @throws IllegalAccessException  * @throws InstantiationException  * @throws ClassNotFoundException  * @throws InvocationTargetException  * @throws IllegalArgumentException  * @throws SecurityException  * @throws NoSuchMethodException  */public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {createObj1();createObj2();}//使用带参数的构造方法创建对象public static void createObj2() throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{   //Person person = new Person("小红",20);//获取字节码文件对象---Person.classClass<?> claz = Class.forName("com.qianfeng.reflect.Person");//得到构造方法所属的Constructor类型的对象Constructor<?> constructor = claz.getConstructor(String.class,int.class);//使用构造方法创建对象--使用Constructor提供的创建对象的功能Person person =(Person)constructor.newInstance("小红",20);System.out.println(person);}//当空参的构造方法不存在时，会发生InstantiationException//当构造方法的权限过低时，会发生IllegalAccessExceptionpublic static void createObj1() throws ClassNotFoundException, InstantiationException, IllegalAccessException{//Person person = new Person();//获取字节码文件对象---Person.classClass<?> claz = Class.forName("com.qianfeng.reflect.Person");//使用Class提供的newInstance()方法创建Person类型的对象Object obj = claz.newInstance();//使用空参的构造方法创建对象Person person = (Person)obj;System.out.println(person);}}

import java.lang.reflect.Field;public class Demo3 {/** * 动态创建对象并给属性赋值 * @throws ClassNotFoundException  * @throws SecurityException  * @throws NoSuchFieldException  * @throws IllegalAccessException  * @throws InstantiationException  */public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, SecurityException, InstantiationException, IllegalAccessException {//Person person = new Person();//person.setName("小红");//获取字节码文件对象---Person.class     Class<?> claz = Class.forName("com.qianfeng.reflect.Person");          //得到属性name所属的 Field类型的对象     //Field field = claz.getField("name");//只能获取权限是public 的属性     //System.out.println(field);//NoSuchFieldException          Field field = claz.getDeclaredField("name");          //因为name是非静态属性，所以必须通过对象访问，所以先创建对象     Object obj = claz.newInstance();          //设置name属性为可访问的     field.setAccessible(true);// 该方法是从父类中继承的          //使用Field类提供的赋值功能，给属性赋值     field.set(obj, "小红");          System.out.println(obj);          }}

import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;public class Demo4 {/** * 动态创建对象，并调用方法 * @throws InvocationTargetException  * @throws IllegalArgumentException  * @throws IllegalAccessException  * @throws InstantiationException  * @throws SecurityException  * @throws NoSuchMethodException  * @throws ClassNotFoundException  */public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {method1();method2();method3();}//调用静态方法public static void method3() throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{//获取字节码文件对象---Person.class     Class<?> claz = Class.forName("com.qianfeng.reflect.Person");          ///获取被调用的方法所属的 Method类型的对象     Method method = claz.getMethod("function", null);          //执行方法     method.invoke(null, null);     }//调用带参的构造方法public static void method2() throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{//获取字节码文件对象---Person.class     Class<?> claz = Class.forName("com.qianfeng.reflect.Person");        //获取被调用的方法所属的 Method类型的对象     Method method = claz.getMethod("fun", String.class);          //fun()属于非静态方式，需要对象去调用     Object obj = claz.newInstance();          //执行方法     method.invoke(obj, "hello");}//调用无参的构造方法public static void method1() throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{// Person person = new Person();person.show();//获取字节码文件对象---Person.class     Class<?> claz = Class.forName("com.qianfeng.reflect.Person");          //获取被调用的方法所属的 Method类型的对象     Method method = claz.getMethod("show", null);               //show()属于非静态方式，需要对象去调用     Object obj = claz.newInstance();          //执行方法     method.invoke(obj, null);          }}