Java -- 反射示例

1. 反射： 即加载和解剖， 用于设计框架， 读取配置档 动态创建对象。

Person类，用于反射。

package com.kevin.class_test;

public class Person {

	public String namestr="aaaa";

	public Person()
	{
		System.out.println("public constructor");
	}
	private Person(String name)
	{
		System.out.println("private constructor " + name);
	}
	public Person(String name1, String name2)
	{
		System.out.println("public constructor " + name1 + name2);
	}

	public void fun()
	{
		System.out.println("in fun: " + namestr);
	}

	public String fun(String name)
	{
		System.out.println("in fun: " + namestr + name);
		return "Yes";
	}

	public static void main(String[] args)
	{
		System.out.println("in main");
		for(String str : args)
		{
			System.out.println(str);
		}
	}
}

反射的使用实例， 使用Junit测试

package com.kevin.class_test;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class JunitTest {

	Class clazz = null;  //建立Class对象

	@Before
	public void before() throws Exception  //初始化@before
	{
		System.out.println("before");
		clazz = Class.forName("com.kevin.class_test.Person");  //加载类，一定要用类全名
	}

	@Test
	public void test() throws Exception {
		Person person = (Person) clazz.newInstance();  //反射实例化对象
		person.fun();
	}

	@Test
	public void test2() throws Exception {
		Constructor cons = clazz.getDeclaredConstructor(String.class);  //反射获取private方法
		cons.setAccessible(true);      //改变private属性
		Person person = (Person) cons.newInstance("kevin");  //使用获取的构造器 实例化对象
		person.fun();
	}

	@Test
	public void test3() throws Exception {
		Person p = new Person();
		Method method = clazz.getMethod("fun", String.class);    //反射获取public方法
		String result = (String) method.invoke(p, "xiang");
		System.out.println("result: " + result);
	}

	@Test
	public void test4() throws Exception {
		Method method = clazz.getMethod("main", String[].class);  //反射获取main方法
		method.invoke(null, (Object)new String[]{"a","b"});     //必须将String[]掩饰为Object，不然会参数异常报错
	}

	@Test
	public void test5() throws Exception {
		Person p = new Person();
		Field field = clazz.getField("namestr");          //反射获取属性
		Object value = field.get(p);           //获取属性值
		Class type = field.getType();          //获取属性值类型
		if( type.equals(String.class) )
		{
			String str = (String)value;     //类型转换
			System.out.println("str: " + str);
		}
		field.set(p, "bbbb");         //修改属性
		System.out.println("str: " + p.namestr);
	}

	@After
	public void after()
	{
		System.out.println("atfer");
	}
}