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個例子讓你了解Java反射機制

原文地址：http://blog.csdn.net/ljphhj/article/details/12858767

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JAVA反射機制：

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通俗地說,反射機制就是可以把一個類,類的成員(函數(shù),屬性),當(dāng)成一個對象來操作,希望讀者能理解,也就是說,類,類的成員,我們在運行的時候還可以動態(tài)地去操作他們.

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理論的東東太多也沒用，下面我們看看實踐 Demo?～

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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 {/*** 為了看清楚Java反射部分代碼，所有異常我都最后拋出來給虛擬機處理！* @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. 通過Java反射機制得到類的包名和類名 Demo1();System.out.println("===============================================");//Demo2. 驗證所有的類都是Class類的實例對象 Demo2();System.out.println("===============================================");//Demo3. 通過Java反射機制，用Class 創(chuàng)建類對象[這也就是反射存在的意義所在]，無參構(gòu)造 Demo3();System.out.println("===============================================");//Demo4: 通過Java反射機制得到一個類的構(gòu)造函數(shù)，并實現(xiàn)構(gòu)造帶參實例對象 Demo4();System.out.println("===============================================");//Demo5: 通過Java反射機制操作成員變量, set 和 get Demo5();System.out.println("===============================================");//Demo6: 通過Java反射機制得到類的一些屬性： 繼承的接口，父類，函數(shù)信息，成員信息，類型等 Demo6();System.out.println("===============================================");//Demo7: 通過Java反射機制調(diào)用類中方法 Demo7();System.out.println("===============================================");//Demo8: 通過Java反射機制獲得類加載器 Demo8();System.out.println("===============================================");}/*** Demo1: 通過Java反射機制得到類的包名和類名*/public static void Demo1(){Person person = new Person();System.out.println("Demo1: 包名: " + person.getClass().getPackage().getName() + "，" + "完整類名: " + person.getClass().getName());}/*** Demo2: 驗證所有的類都是Class類的實例對象* @throws ClassNotFoundException */public static void Demo2() throws ClassNotFoundException{//定義兩個類型都未知的Class , 設(shè)置初值為null, 看看如何給它們賦值成Person類Class<?> class1 = null;Class<?> class2 = null;//寫法1, 可能拋出 ClassNotFoundException [多用這個寫法]class1 = Class.forName("cn.lee.demo.Person");System.out.println("Demo2:(寫法1) 包名: " + class1.getPackage().getName() + "，" + "完整類名: " + class1.getName());//寫法2class2 = Person.class;System.out.println("Demo2:(寫法2) 包名: " + class2.getPackage().getName() + "，" + "完整類名: " + class2.getName());}/*** Demo3: 通過Java反射機制，用Class 創(chuàng)建類對象[這也就是反射存在的意義所在]* @throws ClassNotFoundException * @throws IllegalAccessException * @throws InstantiationException */public static void Demo3() throws ClassNotFoundException, InstantiationException, IllegalAccessException{Class<?> class1 = null;class1 = Class.forName("cn.lee.demo.Person");//由于這里不能帶參數(shù)，所以你要實例化的這個類Person，一定要有無參構(gòu)造函數(shù)哈～Person person = (Person) class1.newInstance();person.setAge(20);person.setName("LeeFeng");System.out.println("Demo3: " + person.getName() + " : " + person.getAge());}/*** Demo4: 通過Java反射機制得到一個類的構(gòu)造函數(shù)，并實現(xiàn)創(chuàng)建帶參實例對象* @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");//得到一系列構(gòu)造函數(shù)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: 通過Java反射機制操作成員變量, 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: 修改屬性之后得到屬性變量的值：" + personNameField.get(obj));}/*** Demo6: 通過Java反射機制得到類的一些屬性： 繼承的接口，父類，函數(shù)信息，成員信息，類型等* @throws ClassNotFoundException */public static void Demo6() throws ClassNotFoundException{Class<?> class1 = null;class1 = Class.forName("cn.lee.demo.SuperMan");//取得父類名稱Class<?> superClass = class1.getSuperclass();System.out.println("Demo6: SuperMan類的父類名: " + superClass.getName());System.out.println("===============================================");Field[] fields = class1.getDeclaredFields();for (int i = 0; i < fields.length; i++) {System.out.println("類中的成員: " + fields[i]);}System.out.println("===============================================");//取得類方法Method[] methods = class1.getDeclaredMethods();for (int i = 0; i < methods.length; i++) {System.out.println("Demo6,取得SuperMan類的方法：");System.out.println("函數(shù)名：" + methods[i].getName());System.out.println("函數(shù)返回類型：" + methods[i].getReturnType());System.out.println("函數(shù)訪問修飾符：" + Modifier.toString(methods[i].getModifiers()));System.out.println("函數(shù)代碼寫法： " + methods[i]);}System.out.println("===============================================");//取得類實現(xiàn)的接口,因為接口類也屬于Class,所以得到接口中的方法也是一樣的方法得到哈Class<?> interfaces[] = class1.getInterfaces();for (int i = 0; i < interfaces.length; i++) {System.out.println("實現(xiàn)的接口類名: " + interfaces[i].getName() );}}/*** Demo7: 通過Java反射機制調(diào)用類方法* @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調(diào)用無參方法fly()：");Method method = class1.getMethod("fly");method.invoke(class1.newInstance());System.out.println("調(diào)用有參方法walk(int m)：");method = class1.getMethod("walk",int.class);method.invoke(class1.newInstance(),100);}/*** Demo8: 通過Java反射機制得到類加載器信息* * 在java中有三種類類加載器。[這段資料網(wǎng)上截取]1）Bootstrap ClassLoader 此加載器采用c++編寫，一般開發(fā)中很少見。2）Extension ClassLoader 用來進行擴展類的加載，一般對應(yīng)的是jre\lib\ext目錄中的類3）AppClassLoader 加載classpath指定的類，是最常用的加載器。同時也是java中默認的加載器。* * @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: 類加載器類名: " + 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("超人會飛耶～～");}public boolean isBlueBriefs() {return BlueBriefs;}public void setBlueBriefs(boolean blueBriefs) {BlueBriefs = blueBriefs;}@Overridepublic void walk(int m) {// TODO Auto-generated method stubSystem.out.println("超人會走耶～～走了" + m + "米就走不動了！");} } interface ActionInterface{public void walk(int m); } View Code

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轉(zhuǎn)載于:https://www.cnblogs.com/luolizhi/p/4943808.html

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