Java基础篇之反射机制详解

目录

• 1、反射概述

• 1.1什么是反射
• 1.2、反射能干什么

• 2.1反射构造方法

• 2.1.1反射无参的构造函数
• 2.1.2反射“一个参数”的构造函数
• 2.1.3反射“多个参数”的构造函数
• 2.1.4反射“私有”的构造函数
• 2.1.5反射得到类中所有的构造函数

package com.cj.test;
import java.util.Date;
public class Person {
	public Person(){
		System.out.println("默认的无参构造方法执行了");
	}
	public Person(String name){
		System.out.println("姓名:"+name);
	}
	public Person(String name,int age){
		System.out.println(name+"="+age);
	}
	private Person(int age){
		System.out.println("年龄:"+age);
	}
	public void m1() {
		System.out.println("m1");
	}
	public void m2(String name) {
		System.out.println(name);
	}
	public String m3(String name,int age) {
		System.out.println(name+":"+age);
		return "aaa";
	}
	private void m4(Date d) {
		System.out.println(d);
	}
	public static void m5() {
		System.out.println("m5");
	}
	public static void m6(String[] strs) {
		System.out.println(strs.length);
	}
        public static void main(String[] args) {
		System.out.println("main");
	}
}

package com.cj.test;
import java.lang.reflect.Method;
import java.util.Date;
import org.junit.Test;
public class Demo2 {
	@Test//public void m1()
	public void test1() throws Exception{
		Class clazz = Class.forName("com.cj.test.Person");
		Person p = (Person)clazz.newInstance();
		Method m = clazz.getMethod("m1", null);
		m.invoke(p, null);
	}
	@Test//public void m2(String name)
	public void test2() throws Exception{
		Class clazz = Person.class;
		Person p = (Person) clazz.newInstance();
		Method m = clazz.getMethod("m2", String.class);
		m.invoke(p, "张三");
	}
	@Test//public String m3(String name,int age)
	public void test3() throws Exception{
		Class clazz = Person.class;
		Person p = (Person) clazz.newInstance();
		Method m = clazz.getMethod("m3", String.class,int.class);
		String returnValue = (String)m.invoke(p, "张三",23);
		System.out.println(returnValue);
	}
	@Test//private void m4(Date d)
	public void test4() throws Exception{
		Class clazz = Person.class;
		Person p = (Person) clazz.newInstance();
		Method m = clazz.getDeclaredMethod("m4", Date.class);
		m.setAccessible(true);
		m.invoke(p,new Date());
	}
	@Test//public static void m5()
	public void test5() throws Exception{
		Class clazz = Person.class;
		Method m = clazz.getMethod("m5", null);
		m.invoke(null,null);
	}
	@Test//private static void m6(String[] strs)
	public void test6() throws Exception{
		Class clazz = Person.class;
		Method m = clazz.getDeclaredMethod("m6",String[].class);
		m.setAccessible(true);
		m.invoke(null,(Object)new String[]{"a","b"});
	}
	@Test
	public void test7() throws Exception{
		Class clazz = Person.class;
		Method m = clazz.getMethod("main",String[].class);
		m.invoke(null,new Object[]{new String[]{"a","b"}});
	}
}

package com.cj.test;
import java.util.Date;
public class Person {
	public String name="李四";
	private int age = 18;
	public static Date time;
	public int getAge() {
		return age;
	}
	public Person(){
		System.out.println("默认的无参构造方法执行了");
	}
	public Person(String name){
		System.out.println("姓名:"+name);
	}
	public Person(String name,int age){
		System.out.println(name+"="+age);
	}
	private Person(int age){
		System.out.println("年龄:"+age);
	}
	public void m1() {
		System.out.println("m1");
	}
	public void m2(String name) {
		System.out.println(name);
	}
	public String m3(String name,int age) {
		System.out.println(name+":"+age);
		return "aaa";
	}
	private void m4(Date d) {
		System.out.println(d);
	}
	public static void m5() {
		System.out.println("m5");
	}
	public static void m6(String[] strs) {
		System.out.println(strs.length);
	}
	public static void main(String[] args) {
		System.out.println("main");
	}
}

package com.cj.test;
import java.lang.reflect.Field;
import java.util.Date;
import org.junit.Test;
public class Demo3 {
	//public String name="李四";
	@Test
	public void test1() throws Exception{
		Class clazz = Person.class;
		Person p = (Person)clazz.newInstance();
		Field f = clazz.getField("name");
		String s = (String)f.get(p);
		System.out.println(s);
		//更改name的值
		f.set(p, "王六");
		System.out.println(p.name);
	}
	@Test//private int age = 18;
	public void test2() throws Exception{
		Class clazz = Person.class;
		Person p = (Person)clazz.newInstance();
		Field f = clazz.getDeclaredField("age");
		f.setAccessible(true);
		int age = (Integer)f.get(p);
		System.out.println(age);
		f.set(p, 28);
		age = (Integer)f.get(p);
		System.out.println(age);
	}
	@Test//public static Date time;
	public void test3() throws Exception{
		Class clazz = Person.class;
		Field f = clazz.getField("time");
		f.set(null, new Date());
		System.out.println(Person.time);
	}
}