java反射机制（笔记）

java反射机制就是获取出class的相应方法

 

例如 获取构造函数：

模版：

Class test = Class.forName("cn.test.Person");//得到相应的class
Constructor test1 = test.getConstructor(null); //获取空的够着函数
Person person = (Person) test1.newInstance(null);//new一个新对象
//这里是访问私有的构造函数，进行暴力反射
Constructor c3 = test3.getDeclaredConstructor(List.class);//获得私有的构造
c3.setAccessible(true);//暴力反射

反射函数模版：

//实例化一个对象
Class classtest = Class.forName("");
Method method = classtest.getMethod("方法名",参数)；//参数多个用逗号隔开
method.invoke(对象,参数);//首先要创建一个实例化类，然后再进行调用

 反射main方法

Class testmain = Class.forName("cn.test.Person");//得到对象
Method tt = testmain.getMethod("main",String[].class);//得到main方法
tt.invoke(null, new Object[]{new String[]{"aa","bbb"}});//调用

 

　得到字段:

Person person = new Person("yy");
        Class cla = Class.forName("cn.test.Person");
        Field field = cla.getField("name");//得到name
        String name = (String) field.get(person);
        System.out.println(name);

 

例子:

//Person类
package cn.test;

import static java.lang.System.out;

import java.awt.List;
public class Person {
	
	private String name;
	
	public Person(){
		out.print("nulllllllll");
	}
	public Person(String name){
		out.println(name);
		this.name = name;
	}
	
	public Person(String name,int n){
		out.print(""+name+"  "+n);
	}
	private Person(List l){
		out.print("static person");
	}
	
	public void getint(int x){
		System.out.println("x=="+x);
	}
	
	
	public static void main(String[] args){
		System.out.print("main ");
	}
}

　　

　

//测试类
package cn.test.test;

import java.awt.List;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

import org.junit.Test;

import cn.test.Person;

public class test {

    @Test
    public void test1() throws Exception{
        Class test = Class.forName("cn.test.Person");
        Constructor test1 = test.getConstructor(null);
        Person person = (Person) test1.newInstance(null);
        
    }
    
    @Test
    public void test2() throws Exception{
        Class test2 = Class.forName("cn.test.Person");
        Constructor c2 = test2.getConstructor(String.class);
        Person person = (Person) c2.newInstance("xxvdfdfd");
        
    }
    @Test
    public void test3() throws Exception{
        Class test3 = Class.forName("cn.test.Person");
        Constructor c3 = test3.getDeclaredConstructor(List.class);
        c3.setAccessible(true);
        Person person = (Person) c3.newInstance(new List());
    }
    
    //反射得到方法
    @Test
    public void test4() throws Exception{
        Person person = new Person();
        Class test4 = Class.forName("cn.test.Person");
        Method  tt = test4.getMethod("getint", int.class);
    
            tt.invoke(person, 12);
            
    }
    //反射得到买你函数
    @Test
    public void testmain() throws Exception{
        Class testmain = Class.forName("cn.test.Person");
        Method tt = testmain.getMethod("main",String[].class);
        tt.invoke(null, new Object[]{new String[]{"aa","bbb"}});
    }

    //反射得到字段
    @Test
    public void getname() throws Exception{
        Person person = new Person("yy");
        Class cla = Class.forName("cn.test.Person");
        Field field = cla.getField("name");//得到name
        String name = (String) field.get(person);
        System.out.println(name);
    }
}