黑马程序员_JAVA反射学习

最新推荐文章于 2015-09-20 16:18:09 发布

原创最新推荐文章于 2015-09-20 16:18:09 发布 · 93 阅读

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本文详细介绍了Java反射机制的应用，通过具体示例展示了如何使用反射来获取类的构造方法、方法和字段等内容。从加载类到获取不同类型的构造方法，再到调用类的方法及修改类的字段，全面解析反射技术。

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反射主要用于框架。

Person类如下：

package com.fly.reflect;

import java.io.InputStream;
import java.util.List;

/*
* Person类，用于反射构造方法
*/
public class Person {
public String name = "aa";
private int password = 1232323;
private static int age = 19;

public Person() {
System.out.println("person");
}

public Person(String name) {
System.out.println("name:" + name);
}

public Person(String name, int age) {
System.out.println("person name:" + name + " age:" + age);
}

private Person(List list) {
System.out.println("list");
}

private Person(int a) {
System.out.println("a==" + a);
}

//测试用
public void testMe() {
System.out.println("可以了");
}

public void aa1() {
System.out.println("aa1");
}

public void aa1(String name, int password) {
System.out.println(name + ":" + password);
}

public Class[] aa1(String name, int[] password) {
return new Class[]{String.class};
}

private void aa1(InputStream in) {
System.out.println(in);
}

public static void aa1(int num) {
System.out.println(num);
}

public static void main(String[] args) {
System.out.println("This is main function");
}
}

一、用反射获取构造方法

反射方法如下：

package com.fly.reflect;

import java.lang.reflect.Constructor;
import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

//反射类的构造函数，创建类的对象
public class Demo1 {
//反射构造函数:public Person()
@Test
public void test1() throws Exception {
//加载类
Class clazz = Class.forName("com.fly.reflect.Person");
//获取空参构造方法
Constructor c = clazz.getConstructor(null);
//创建对象
Person p = (Person)c.newInstance(null);
p.testMe();
}

//反射构造函数:public Person(String name)
@Test
public void test2() throws Exception {
Class clazz = Class.forName("com.fly.reflect.Person");
Constructor c = clazz.getConstructor(String.class);
Person p = (Person)c.newInstance("gaozx");
p.testMe();
}

//反射构造函数:public Person(String name, int age)
@Test
public void test3() throws Exception {
Class clazz = Class.forName("com.fly.reflect.Person");
Constructor c = clazz.getConstructor(String.class, int.class);
Person p = (Person)c.newInstance("gaozx", 12);
p.testMe();
}

//反射构造函数:public Person(List list)
@Test
public void test4() throws Exception {
Class clazz = Class.forName("com.fly.reflect.Person");
//获取私有构造方法
Constructor c = clazz.getDeclaredConstructor(List.class);
c.setAccessible(true); //暴力反射
Person p = (Person)c.newInstance(new ArrayList());
p.testMe();
}

//getDeclaredConstrctor和getConstructor的区别
@Test
public void test5() throws Exception {
Class clazz = Class.forName("com.fly.reflect.Person");
Constructor c = clazz.getConstructor(String.class);
Person p = (Person)c.newInstance("Sim");
p.testMe();
}
}

获取公共构造方法和获取私有构造方法的方法不一样。 clazz.getDeclaredConstructor()也可以用于获取公共构造方法。

二、反射获取类的方法

package com.fly.reflect;

import java.io.FileInputStream;
import java.io.InputStream;
import java.lang.reflect.Method;

import org.junit.Test;

//反射类的方法
public class Demo2 {

//反射类的方法：public void aa1()
@Test
public void test1() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Method method = clazz.getMethod("aa1", null);
method.invoke(p, null);
}

//反射类的方法：public void aa1(String name, int password)
@Test
public void test2() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Method method = clazz.getMethod("aa1", String.class, int.class);
method.invoke(p, "aa", 1);
}

//反射类的方法：public Class[] aa1(String name, int[] password)
@Test
public void test3() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Method method = clazz.getMethod("aa1", String.class, int[].class);
Class[] cs = (Class[]) method.invoke(p, "aa", new int[]{1, 2});
System.out.println(cs[0]);
}

//反射类的方法：private void aa1(InputStream in)
@Test
public void test4() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Method method = clazz.getDeclaredMethod("aa1", InputStream.class);
method.setAccessible(true);
method.invoke(p, new FileInputStream("e:\\1.txt"));
}

//反射类的方法：public static void aa1(int num)
@Test
public void test5() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Method method = clazz.getMethod("aa1", int.class);
method.invoke(null, 11);
}

//反射类的方法：public static void main(String[] args)
@Test
public void test6() throws Exception {
Class clazz = Class.forName("com.fly.reflect.Person");
Method method = clazz.getMethod("main", String[].class);
method.invoke(null, new Object[]{new String[]{"1","2"}});
}
}

三、反射获取类的字段

package com.fly.reflect;

import java.lang.reflect.Field;

import org.junit.Test;

//反射类的字段
public class Demo3 {

//反射字段:public String name = "aa";
@Test
public void test1() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Field f = clazz.getField("name");
//获取字段的类型
Class type = f.getType();
//获取字段的值
Object obj = (String) f.get(p);
System.out.println((String)obj);
f.set(p, "bbbb");
System.out.println(p.name);
}

//反射字段：private int password;
@Test
public void test2() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Field f = clazz.getDeclaredField("password");
f.setAccessible(true);
int pwd = (Integer) f.get(p);
System.out.println(pwd);
f.set(p, 999999);
int pwd1 = (Integer) f.get(p);
System.out.println(pwd1);
}

//反射字段：private static int age = 19
@Test
public void test3() throws Exception {
Person p = new Person();
Class clazz = Class.forName("com.fly.reflect.Person");
Field f = clazz.getDeclaredField("password");
f.setAccessible(true);
int pwd = (Integer) f.get(p);
System.out.println(pwd);
f.set(p, 999999);
int pwd1 = (Integer) f.get(p);
System.out.println(pwd1);
}
}