通俗地說(shuō),反射機(jī)制就是可以把一個(gè)類,類的成員(函數(shù),屬性),當(dāng)成一個(gè)對(duì)象來(lái)操作,希望讀者能理解,也就是說(shuō),類,類的成員,我們?cè)谶\(yùn)行的時(shí)候還可以動(dòng)態(tài)地去操作他們.
理論的東東太多也沒(méi)用，下面我們看看實(shí)踐 Demo ～
Demo:
[java]
view plaincopyprint?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 {
/**
* 為了看清楚Java反射部分代碼，所有異常我都最后拋出來(lái)給虛擬機(jī)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(guò)Java反射機(jī)制得到類的包名和類名
Demo1();
System.out.println("===============================================");
//Demo2. 驗(yàn)證所有的類都是Class類的實(shí)例對(duì)象
Demo2();
System.out.println("===============================================");
//Demo3. 通過(guò)Java反射機(jī)制，用Class 創(chuàng)建類對(duì)象[這也就是反射存在的意義所在]，無(wú)參構(gòu)造
Demo3();
System.out.println("===============================================");
//Demo4: 通過(guò)Java反射機(jī)制得到一個(gè)類的構(gòu)造函數(shù)，并實(shí)現(xiàn)構(gòu)造帶參實(shí)例對(duì)象
Demo4();
System.out.println("===============================================");
//Demo5: 通過(guò)Java反射機(jī)制操作成員變量, set 和 get
Demo5();
System.out.println("===============================================");
//Demo6: 通過(guò)Java反射機(jī)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(guò)Java反射機(jī)制調(diào)用類中方法
Demo7();
System.out.println("===============================================");
//Demo8: 通過(guò)Java反射機(jī)制獲得類加載器
Demo8();
System.out.println("===============================================");
}
/**
* Demo1: 通過(guò)Java反射機(jī)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(yàn)證所有的類都是Class類的實(shí)例對(duì)象
* @throws ClassNotFoundException
*/
public static void Demo2() throws ClassNotFoundException
{
//定義兩個(gè)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(xiě)法1, 可能拋出 ClassNotFoundException [多用這個(gè)寫(xiě)法]
class1 = Class.forName("cn.lee.demo.Person");
System.out.println("Demo2:(寫(xiě)法1) 包名: " + class1.getPackage().getName() + "，"
+ "完整類名: " + class1.getName());
//寫(xiě)法2
class2 = Person.class;
System.out.println("Demo2:(寫(xiě)法2) 包名: " + class2.getPackage().getName() + "，"
+ "完整類名: " + class2.getName());
}
/**
* Demo3: 通過(guò)Java反射機(jī)制，用Class 創(chuàng)建類對(duì)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(shí)例化的這個(gè)類Person，一定要有無(wú)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(guò)Java反射機(jī)制得到一個(gè)類的構(gòu)造函數(shù)，并實(shí)現(xiàn)創(chuàng)建帶參實(shí)例對(duì)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(guò)Java反射機(jī)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(guò)Java反射機(jī)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(wèn)修飾符：" + Modifier.toString(methods[i].getModifiers()));
System.out.println("函數(shù)代碼寫(xiě)法： " + methods[i]);
}
System.out.println("===============================================");
//取得類實(shí)現(xiàn)的接口,因?yàn)榻涌陬愐矊儆贑lass,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(shí)現(xiàn)的接口類名: " + interfaces[i].getName() );
}
}
/**
* Demo7: 通過(guò)Java反射機(jī)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(wú)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(guò)Java反射機(jī)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(xiě)，一般開(kāi)發(fā)中很少見(jiàn)。
2）Extension ClassLoader 用來(lái)進(jìn)行擴(kuò)展類的加載，一般對(duì)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(shí)也是java中默認(rèn)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(huì)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(huì)走耶～～走了" + m + "米就走不動(dòng)了！");
}
}
interface ActionInterface{
public void walk(int m);
}
個(gè)人覺(jué)得使用反射機(jī)制的一些地方：
1.工廠模式：Factory類中用反射的話，添加了一個(gè)新的類之后，就不需要再修改工廠類Factory了
2.數(shù)據(jù)庫(kù)JDBC中通過(guò)Class.forName(Driver).來(lái)獲得數(shù)據(jù)庫(kù)連接驅(qū)動(dòng)
3.分析類文件：畢竟能得到類中的方法等等
4.訪問(wèn)一些不能訪問(wèn)的變量或?qū)傩裕浩平鈩e人代碼
