[Java知识库]java(六) —— 反射

package com.reflection;



import org.junit.Test;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Calendar;
import java.util.Properties;

public class ReflectionTest {

    /**
     * 注意：1.单元测试需要用junit4  2.单元测试必须要public
     * @throws NoSuchMethodException
     * @throws IllegalAccessException
     * @throws InvocationTargetException
     * @throws InstantiationException
     */
    @Test
    public void reflectionStudy() throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {

        //调用非私有的
        //1.获得person类对象
        Class<Person> personClass = Person.class;

        //2.获得其构造器
        Constructor<Person> constructor = personClass.getConstructor(String.class, int.class);
        Person p1 = constructor.newInstance("张三", 12);
        System.out.println(p1.toString());

        //3.获得其属性
        Field name = personClass.getDeclaredField("age");
        //修改属性的方法  set
        name.set(p1,14);
        System.out.println(p1.toString());

        //4.调用方法
        Method showNation = personClass.getDeclaredMethod("showNation", String.class);
        Object showNationInvoke = showNation.invoke(p1, "中国");

        //调用私有的
        //5.私有的构造器
        Constructor<Person> declaredConstructor = personClass.getDeclaredConstructor(String.class);
        //接下来是访问private的核心方法
        declaredConstructor.setAccessible(true);
        Person p2 = declaredConstructor.newInstance("王五");
        System.out.println(p2.toString());

        //6.私有的属性
        Field name1 = personClass.getDeclaredField("name");
        name1.setAccessible(true);
        name1.set(p2,"赵六");
        System.out.println(p2.toString());

        //7.私有的方法
        Method showMe = personClass.getDeclaredMethod("showMe", String.class);
        showMe.setAccessible(true);
        Object act = showMe.invoke(p2, "跳跃");
        System.out.println(act);

    }

    /**
     * 加载Class类的实例的四种方法
     */
    @Test
    public void reflectionStudy1() throws ClassNotFoundException {
        //1.采用该类.class方法
        Class<Person> personClass = Person.class;

        //2.采用该类对象.getclass()方法
        Person person = new Person();
        Class<? extends Person> personClass1 = person.getClass();

        //3.采用Class.forName(地址)方法   这个方法最常用，最能够体现出java动态性特点来
        Class<?> forName = Class.forName("com.reflection.Person");

        //4.采用类加载器
        ClassLoader classLoader = ReflectionTest.class.getClassLoader();
        Class<?> loadClass = classLoader.loadClass("com.reflection.Person");

        //这四种方法都是一个地址
        System.out.println(personClass==personClass1);
        System.out.println(personClass==forName);
        System.out.println(personClass==loadClass);


    }

    /**
     * 加载配置文件
     * 注意在settings->Editor->FileEncodings里将配置文件默认编码选为utf-8并且选中旁边的对勾
     * @throws IOException
     */
    @Test
    public void reflectionStudy2() throws IOException {
        //第一种加载方式，此时默认加载src文件夹下，当处理web项目时，一般多用此种方法
//        Properties properties = new Properties();
//        ClassLoader classLoader = ReflectionTest.class.getClassLoader();
//        InputStream resourceAsStream = classLoader.getResourceAsStream("data1.properties");
//        properties.load(resourceAsStream);
//        Object user = properties.get("user");
//        Object password = properties.get("password");
//        System.out.println(user+"\t"+password);

        //第二种加载方式，此时默认加载当前module下
        Properties properties = new Properties();
        FileInputStream fileInputStream = new FileInputStream("data2.properties");
        FileInputStream fileInputStream1 = new FileInputStream("src\\data1.properties");
        properties.load(fileInputStream1);
        Object user = properties.get("user");
        Object password = properties.get("password");
        System.out.println(user+"\t"+password);

    }

}

package com.reflection;

public class Person {
    private String name;
    public int age;

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public Person() {
    }

    private Person(String name) {
        this.name=name;
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    private void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void showNation(String nation) {
        System.out.println("我是" + nation);
    }

    private String showMe(String activity) {
        System.out.println("我可以" + activity);
        return activity;
    }
}