Java.lang.reflect 下的Class，Method，Field的使用实例

本文目录：一、自己编写的反射练习的Demo; 

                    二、编写一个实例，如何通过反射获取一个类中private 字段的值

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一、自己编写的反射练习的Demo; 

建立一个实体：Book.java

package testdb;import java.math.BigDecimal;public class Book {private int id;private String book_Type;private String book_Name;public BigDecimal sale_Price;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getBook_Type() {return book_Type;}public void setBook_Type(String book_Type) {this.book_Type = book_Type;}public String getBook_Name() {//System.out.println("掉眼泪该方法，book_Name:"+book_Name);return book_Name;}public void setBook_Name(String book_Name) {this.book_Name = book_Name;}public BigDecimal getSale_Price() {return sale_Price;}public void setSale_Price(BigDecimal sale_Price) {this.sale_Price = sale_Price;} }

2、编写实例 main 类

package testdb;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.lang.reflect.Modifier;public class BookTest {//------------Class 3种方式获得类对象public void classTest() throws InstantiationException, IllegalAccessException{Class demo1=null;Class demo2=null;Class demo3=null;try {//1、类对象   Class.forName()demo1 = Class.forName("testdb.Book");} catch (Exception e) {e.printStackTrace();}System.out.println("第一种方式（Class.forName()）：-----------"+demo1);//-------------------方式2开始------------------------------Book book = new Book();Object ob  =book;System.out.println("第2种方式：ob.getClass()= ---------------"+ob.getClass());System.out.println("第2种方式：book.getClass()= ---------------"+book.getClass());//---------------------方式3开始-------------------------------------demo3 = Book.class;System.out.println("第三种方式获取类对象（demo3 = Book.class;）：----------"+demo3);//-----------------------将类对象实例化-----------------------------------------------System.out.println("将类对象实例化: "+demo3.newInstance());}//------------Fieldpublic  void showClass( Class cl ){ Field [] fl = cl.getDeclaredFields();//得到类的所有对象(可以将私有属性获取出来) for(Field fl1:fl){System.out.println("对象名称----"+fl1.getName()); fl1.getName();//获取对象的名称System.out.println("对象类型----"+fl1.getType());fl1.getType();//获取属性对象类型 } System.out.println("-----------------------------------------------------------");  Field [] fle = cl.getFields();//得到类的所有对象(只可以将公有属性获取出来)  for(Field fl1:fle){System.out.println("对象名称222----"+fl1.getName()); fl1.getName();//获取对象的名称System.out.println("对象类型----"+fl1.getType());fl1.getType();//获取属性对象类型 }}public  void showClass(Object ob) throws IllegalArgumentException, IllegalAccessException{Class cl = ob.getClass();Field [] fl = cl.getDeclaredFields();//得到类的所有对象(可以将私有属性获取出来) for(Field fl1:fl){ fl1.setAccessible(true);System.out.println("对象名称ob----"+fl1.getName()+"---"+fl1.get(ob)); fl1.getName();//获取对象的名称  }}//------------------------Method1------------获取类对象方法public void showMethod(Object ob) throws ClassNotFoundException{Class cl =  ob.getClass();Method [] methods = cl.getDeclaredMethods();//获得对象的所有方法for(Method med:methods){System.out.println("方法名----"+med.getName()); //获取对象方法名System.out.println("方法修饰符----"+Modifier.toString(med.getModifiers()));//public  private ...System.out.println("方法返回值类型----"+med.getReturnType());//方法返回值//方法参数列表 set方法Class[] proType= med.getParameterTypes();System.out.println("方法参数列表");for(Class type:proType){System.out.println("参数类型："+type.getName());}}}//--------------------Method2---------------------------操作类对象值public void showMethod2(Object ob) throws ClassNotFoundException, SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException{Class cl = ob.getClass(); Method me = cl.getMethod("getBook_Name", null); me.invoke(ob, null); System.out.println(me.invoke(ob, null)); System.out.println("---------------------------------"); Method me2 = cl.getMethod("setBook_Name", String.class); me2.invoke(ob, "平凡的世界");//相当于book.setBook_Name 设值方法  Method me3 = cl.getMethod("getBook_Name", null); me3.invoke(ob, null); System.out.println(me3.invoke(ob, null));//相当于book.getBook_Name 取值方法}/** * @param args * @throws ClassNotFoundException  * @throws IllegalAccessException  * @throws IllegalArgumentException  * @throws InstantiationException  * @throws InvocationTargetException  * @throws NoSuchMethodException  * @throws SecurityException  */public static void main(String[] args) throws ClassNotFoundException, IllegalArgumentException, IllegalAccessException, InstantiationException, SecurityException, NoSuchMethodException, InvocationTargetException {// TODO Auto-generated method stub//新建一本书Book book = new Book();Class cl= Class.forName("java.lang.String");book.setId(1);book.setBook_Name("《和空姐同居的日子》");book.setBook_Type("言情");//BookTest bt = new BookTest();//bt.classTest();//bt.showClass(book);//bt.showClass(Class.forName("testdb.Book"));bt.showMethod2(book);System.out.println(book.getBook_Name());}}

二、编写一个实例，如何通过反射获取一个类中private 字段的值

1、编写一个实体：

package ww;public class BeanTest {      private int count;    public <span style="font-family: Arial, Helvetica, sans-serif;">BeanTest</span><span style="font-family: Arial, Helvetica, sans-serif;">(String str) {</span>super();this.count = str.length();} }

2、main 代码：

public class demoTest {        public static void main(String[] args) throws Exception{               <span style="font-family: Arial, Helvetica, sans-serif;">beanTest</span><span style="font-family: Arial, Helvetica, sans-serif;">  </span><span style="font-family: Arial, Helvetica, sans-serif;"> test = new   </span><span style="font-family: Arial, Helvetica, sans-serif;">beanTest</span><span style="font-family: Arial, Helvetica, sans-serif;">("abcdsef");</span> Field f = beanTest.class.getDeclaredField("count");//其中,最关键的代码是://f.setAccessible(true);//这行代码把对象data上的name字段设置为public访问属性.f.setAccessible(true);System.out.println(f.get(test)); }}

运行结果：7

PS----确实不是很清楚，java 的一大特性就是封装，保障数据安全；  但是这里却能通过反射访问被封装的数据。