Java_反射技术_简述

来源：互联网发布：淘宝买的假落红好用吗? 编辑：程序博客网时间：2024/05/22 08:06

学习笔记：反射

提出一个问题

String classPath=”cn.itcast.Cat”

需求，请把该类的所有方法和属性得到.

反射原理图：

1. 使用反射技术得到构造函数，并实例化对象

所有的操作都是对Cat.java

packagecn.itcast.reflection; importjava.util.List; public class Cat {     public Stringname=”麦当劳”;    private int age;    private String[]foods;    public Cat(){             // TODO Auto-generated constructor stub    }    publicCat(String []foods){       this.foods=foods;    }       public void show(){       System.out.println("猫猫叫w");    }    //添加一个带有参数的函数    public void show(String name){       System.out.println("猫猫叫"+name);    }    //有两个参数的普通函数    public void show(String name,int age){       System.out.println(name+" 年龄是"+age);    }       //猫猫数数    private void count(List list){             for(Object obj: list)       {           System.out.println(obj);       }    }       publicCat(String name,int age){       this.name=name;       this.age=age;    }     public StringgetName() {       return name;    }     public void setName(String name) {       this.name = name;    }     public int getAge() {       return age;    }     public void setAge(int age) {       this.age = age;    }     publicString[] getFoods() {       return foods;    }     public void setFoods(String[] foods) {       this.foods = foods;    }   }

案例1

//使用默认的构造函数来实例化对象    private static void test1() throws InstantiationException,           IllegalAccessException {       // TODO Auto-generated method stub       Class clazz=Cat.class;       //实例化Cat       Cat cat=(Cat) clazz.newInstance();       //测试       cat.show();    }

案例2

//用 public Cat(String name,int age)来实例化对象    private static void test2() throws NoSuchMethodException,           SecurityException,InstantiationException, IllegalAccessException,           IllegalArgumentException,InvocationTargetException {             Class clazz =Cat.class;       //得到该构造方法,希望得到       Constructorc=clazz.getConstructor(String.class,int.class);             //创建实例       Cat cat=(Cat) c.newInstance("小白",2); //相当于 Cat cat=new Cat("小白",2);       System.out.println(cat.getName());       cat.show();    }

案例3

//得到 public Cat(String []foods) 构造函数    private static void test3() throws NoSuchMethodException,           SecurityException,InstantiationException, IllegalAccessException,           IllegalArgumentException,InvocationTargetException {             //1.得到Class 对象       Class clazz = Cat.class;       //2.通过clazz得打构造       Constructor c=clazz.getConstructor(String[].class);       //3.通过c 来创建Cat 实例       //Cat cat=(Cat) c.newInstance((Object) new String[]{"鱼","老鼠"});//因为newInstance接受可变参数,"鱼"，"老鼠" // newInstance("鱼","老鼠")       Cat cat=(Cat) c.newInstance(new Object[]{ new String[]{"鱼","老鼠"}});//因为newInstance接受可变参数,"鱼"，"老鼠" // newInstance("鱼","老鼠")       cat.show();    }

2. 使用反射技术,得到成员函数，并调用.

案例1

//反射 public void show()，并调用.    private static void test1() throws Exception {             //1.得到Class对象       Class clazz = Class.forName("cn.itcast.reflection.Cat");       //2.得到show方法       Method m=clazz.getMethod("show",null);       //3.调用       m.invoke(clazz.newInstance(),null); //同学会不好理解clazz.newInstance().invoke(m,"");    }

案例2

////反射public void show(String name)    private static void test2() throws Exception {       //反射public void show(String name)       Class clazz = Class.forName("cn.itcast.reflection.Cat");       //得到show(String name)       Method m=clazz.getMethod("show",String.class);       //调用       m.invoke(clazz.newInstance(), "宋江"); // show("宋江");    }

案例3

//反射 public void show(String name,intage)    private static void test3() throws Exception {             Class clazz = Class.forName("cn.itcast.reflection.Cat");       Method m=clazz.getMethod("show", String.class,int.class);       m.invoke(clazz.newInstance(), "贾宝玉",12);    }

案例4

//反射private void count(List list)    private static void test4() throws Exception {             Class clazz = Class.forName("cn.itcast.reflection.Cat");       //Method m=clazz.getMethod("count", List.class);//当一个函数是私有的，则不能使用 getMethod       Method m=clazz.getDeclaredMethod("count", List.class);       m.setAccessible(true);//暴力访问.       List al=new ArrayList();       al.add(1);al.add(3);       m.invoke(clazz.newInstance(), al);    }

3. 使用反射得到字段

案例1:

//反射public  String name="麦当劳";    private static void test1() throws Exception {             //Cat cat=new Cat();       Class clazz=Cat.class;       Field f=clazz.getField("name");             //取得f的值.       String name=(String)f.get(clazz.newInstance()); //cat.get(f); //返回Object就是name的值       System.out.println(name);    }

案例2:

//得到private int age;private static void test2() throws Exception {Class clazz = Cat.class;Field f=clazz.getDeclaredField("age");f.setAccessible(true);//这是创建猫的实例Cat cat=(Cat) clazz.newInstance();//给f字段赋值.cat表示给哪个实例赋值.f.set(cat, 13);//取出f.get(cat) 取出cat这个实例的f字符的值System.out.println(f.get(cat));}

0 0