Java反射

最新推荐文章于 2022-08-18 09:03:07 发布
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博客围绕Java反射展开，反射是Java的重要特性，能在运行时动态获取类的信息、调用方法等，在框架开发、测试等场景有广泛应用，可增强程序的灵活性和扩展性。
package com.company;

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;

public class Main {
    /**
     * 为了看清楚Java反射部分代码，所有异常我都最后抛出来给虚拟机处理！
     * @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.  通过Java反射机制得到类的包名和类名
        Demo1();
        System.out.println("===============================================");

        //Demo2.  验证所有的类都是Class类的实例对象
        Demo2();
        System.out.println("===============================================");

        //Demo3.  通过Java反射机制，用Class 创建类对象[这也就是反射存在的意义所在]，无参构造
        Demo3();
        System.out.println("===============================================");

        //Demo4:  通过Java反射机制得到一个类的构造函数，并实现构造带参实例对象
        Demo4();
        System.out.println("===============================================");

        //Demo5:  通过Java反射机制操作成员变量, set 和 get
        Demo5();
        System.out.println("===============================================");

        //Demo6: 通过Java反射机制得到类的一些属性： 继承的接口，父类，函数信息，成员信息，类型等
        Demo6();
        System.out.println("===============================================");

        //Demo7: 通过Java反射机制调用类中方法
        Demo7();
        System.out.println("===============================================");

        //Demo8: 通过Java反射机制获得类加载器
        Demo8();
        System.out.println("===============================================");

    }

    /**
     * Demo1: 通过Java反射机制得到类的包名和类名
     */
    public static void Demo1()
    {
        Person person = new Person();
        System.out.println("Demo1: 包名: " + person.getClass().getPackage().getName() + "，"
                + "完整类名: " + person.getClass().getName());
    }

    /**
     * Demo2: 验证所有的类都是Class类的实例对象
     * @throws ClassNotFoundException
     */
    public static void Demo2() throws ClassNotFoundException
    {
        //定义两个类型都未知的Class , 设置初值为null, 看看如何给它们赋值成Person类
        Class<?> class1 = null;
        Class<?> class2 = null;

        //写法1, 可能抛出 ClassNotFoundException [多用这个写法]
        class1 = Class.forName("com.company.Person");
        System.out.println("Demo2:(写法1) 包名: " + class1.getPackage().getName() + "，"
                + "完整类名: " + class1.getName());

        //写法2
        class2 = Person.class;
        System.out.println("Demo2:(写法2) 包名: " + class2.getPackage().getName() + "，"
                + "完整类名: " + class2.getName());
    }

    /**
     * Demo3: 通过Java反射机制，用Class 创建类对象[这也就是反射存在的意义所在]
     * @throws ClassNotFoundException
     * @throws IllegalAccessException
     * @throws InstantiationException
     */
    public static void Demo3() throws ClassNotFoundException, InstantiationException, IllegalAccessException
    {
        Class<?> class1 = null;
        class1 = Class.forName("com.company.Person");
        //由于这里不能带参数，所以你要实例化的这个类Person，一定要有无参构造函数哈～
        Person person = (Person) class1.newInstance();
        person.setAge(14);
        person.setName("Alipay");
        System.out.println("Demo3: " + person.getName() + " : " + person.getAge());
    }

    /**
     * Demo4: 通过Java反射机制得到一个类的构造函数，并实现创建带参实例对象
     * @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("com.company.Person");
        //得到一系列构造函数集合
        Constructor<?>[] constructors = class1.getConstructors();

        person1 = (Person) constructors[0].newInstance();
        person1.setAge(14);
        person1.setName("Alipay");

        person2 = (Person) constructors[1].newInstance(19,"Alibaba");

        System.out.println("Demo4: " + person1.getName() + " : " + person1.getAge()
                + "  ,   " + person2.getName() + " : " + person2.getAge()
        );

    }

    /**
     * Demo5: 通过Java反射机制操作成员变量, 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("com.company.Person");
        Object obj = class1.newInstance();

        Field personNameField = class1.getDeclaredField("name");
        personNameField.setAccessible(true);
        personNameField.set(obj, "Alipay");


        System.out.println("Demo5: 修改属性之后得到属性变量的值：" + personNameField.get(obj));

    }


    /**
     * Demo6: 通过Java反射机制得到类的一些属性： 继承的接口，父类，函数信息，成员信息，类型等
     * @throws ClassNotFoundException
     */
    public static void Demo6() throws ClassNotFoundException
    {
        Class<?> class1 = null;
        class1 = Class.forName("com.company.SuperMan");

        //取得父类名称
        Class<?>  superClass = class1.getSuperclass();
        System.out.println("Demo6:  SuperMan类的父类名: " + superClass.getName());

        System.out.println("===============================================");


        Field[] fields = class1.getDeclaredFields();
        for (int i = 0; i < fields.length; i++) {
            System.out.println("类中的成员: " + fields[i]);
        }
        System.out.println("===============================================");


        //取得类方法
        Method[] methods = class1.getDeclaredMethods();
        System.out.println("Demo6,取得SuperMan类的方法：");
        for (int i = 0; i < methods.length; i++) {
            System.out.println("-------------------------");
            System.out.println("函数名：" + methods[i].getName());
            System.out.println("函数返回类型：" + methods[i].getReturnType());
            System.out.println("函数访问修饰符：" + Modifier.toString(methods[i].getModifiers()));
            System.out.println("函数代码写法： " + methods[i]);
        }

        System.out.println("===============================================");

        //取得类实现的接口,因为接口类也属于Class,所以得到接口中的方法也是一样的方法得到哈
        Class<?> interfaces[] = class1.getInterfaces();
        for (int i = 0; i < interfaces.length; i++) {
            System.out.println("实现的接口类名: " + interfaces[i].getName() );
        }

    }

    /**
     * Demo7: 通过Java反射机制调用类方法
     * @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("com.company.SuperMan");

        System.out.println("Demo7: \n调用无参方法fly()：");
        Method method = class1.getMethod("fly");
        method.invoke(class1.newInstance());

        System.out.println("调用有参方法walk(int m)：");
        method = class1.getMethod("walk",int.class);
        method.invoke(class1.newInstance(),100);

        System.out.println("使用已有实例调用有参方法walk(int m)：");
        //推荐用如下方式获得构造函数
        Constructor constructor=class1.getConstructor(int.class,java.lang.String.class);
        SuperMan superMan = (SuperMan) constructor.newInstance(14,"Alipay");
        method.invoke(superMan,666);
    }

    /**
     * Demo8: 通过Java反射机制得到类加载器信息
     *
     * 在java中有三种类类加载器。[这段资料网上截取]
     1）Bootstrap ClassLoader 此加载器采用c++编写，一般开发中很少见。
     2）Extension ClassLoader 用来进行扩展类的加载，一般对应的是jre\lib\ext目录中的类
     3）AppClassLoader 加载classpath指定的类，是最常用的加载器。同时也是java中默认的加载器。
     *
     * @throws ClassNotFoundException
     */
    public static void Demo8() throws ClassNotFoundException
    {
        Class<?> class1 = null;
        class1 = Class.forName("com.company.SuperMan");
        String nameString = class1.getClassLoader().getClass().getName();

        System.out.println("Demo8: 类加载器类名: " + 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 SuperMan() {
    }

    public SuperMan(int age, String name, boolean blueBriefs) {
        super(age, name);
        BlueBriefs = blueBriefs;
    }

    public SuperMan(int age, String name) {
        super(age, name);
    }

    public void fly()
    {
        System.out.println((getName()!=null?getName():"Alibaba")+" is flying～～");
    }

    public boolean isBlueBriefs() {
        return BlueBriefs;
    }
    public void setBlueBriefs(boolean blueBriefs) {
        BlueBriefs = blueBriefs;
    }

    @Override
    public void walk(int m) {
        System.out.println((getName()!=null?getName():"Alibaba")+" is walking～～走了" + m + "米就走不动了！");
    }
}
interface ActionInterface{
    public void walk(int m);
}