閒來無事無事,重新看看java的一些知識。這也是Spring中IOC中的基礎。
反射機制的使用目的,就是爲了靈活動態加載需要的對象。
如下的代碼,非常簡單明瞭的介紹了java的反射機制的使用。
轉載自http://blog.csdn.net/ljphhj/article/details/12858767
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 { /** * 爲了看清楚Java反射部分代碼,所有異常我都最後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 創建類對象[這也就是反射存在的意義所在],無參構造 Demo3(); System.out.println("==============================================="); //Demo4: 通過Java反射機制得到一個類的構造函數,並實現構造帶參實例對象 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,函數信息,成員信息,類型等 Demo6(); System.out.println("==============================================="); //Demo7: 通過Java反射機制調用類中方法 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 , 設置初值爲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2 class2 = 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"); //由於這裏不能帶參數,所以你要實例化的這個類Person,一定要有無參構造函數哈~ 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造函數,並實現創建帶參實例對象 * @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"); //得到一系列構造函數集合 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: 修改屬性之後得到屬性變量的值:" + 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("函數名:" + methods[i].getName()); System.out.println("函數返回類型:" + methods[i].getReturnType()); System.out.println("函數訪問修飾符:" + Modifier.toString(methods[i].getModifiers())); System.out.println("函數代碼寫法: " + methods[i]); } System.out.println("==============================================="); //取得類實現的接口,因爲接口類也屬於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("實現的接口類名: " + interfaces[i].getName() ); } } /** * Demo7: 通過Java反射機制調用類方法 * @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調用無參方法fly():"); Method method = class1.getMethod("fly"); method.invoke(class1.newInstance()); System.out.println("調用有參方法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。[這段資料網上截取] 1)Bootstrap ClassLoader 此加載器採用c++編寫,一般開發中很少見。 2)Extension ClassLoader 用來進行擴展類的加載,一般對應的是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; } @Override public void walk(int m) { // TODO Auto-generated method stub System.out.println("超人會走耶~~走了" + m + "米就走不動了!"); } } interface ActionInterface{ public void walk(int m); }