java反射机制的简单使用

import java.lang.reflect.Constructor;
import java.util.Arrays;

import org.junit.Test;
/**
*定义一个Worker类来作为示例
*/
class Worker{
    String name;
    int age;
    int salary;
    Worker() {
        
    }
    
    Worker(String name, int age, int salary) {
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
    
    void show(){
        System.out.println("姓名" + name);
        System.out.println("年龄" + age);
    }
    
    public String toString() {
        return "Worker [name=" + name + ", age=" + age + ", salary=" + salary
                + "]";
    }
    
}


/**
*通过反射机制获取运行时类的对象的几种方法示例
*/
public class TestReflection {
    public static void main(String[] args) throws Exception {
//      1.通过对象调用getClass方法得到运行时类的对象
        Worker w1 = new Worker("Jhon", 20, 20000);
        Class<Worker> clazz1 = (Class<Worker>) w1.getClass(); 
        Worker w2 = (Worker)(clazz1.newInstance());
        w2.show();
        System.out.println(clazz1);
        
//      2.通过类来获取运行时类的对象
        Class clazz2 = Worker.class;
        System.out.println(clazz2);
        
//      3.通过Class.forName(String name)获得运行时类的对象
        Class clazz3 = Class.forName("Worker");                //注：如果worker类不在缺省包中，括号里面要以包名开头
        System.out.println(clazz3);
        
//      4.通过类的加载器来加载运行时类的对象
        Class clazz4 = ClassLoader.getSystemClassLoader().loadClass("Worker");   //注：如果worker类不在缺省包中，括号里面要以包名开头
        System.out.println(clazz4);
        
//      得到构造方法并调用对应对象的方法
        Constructor constructor1 = clazz4.getDeclaredConstructor();
        (clazz1.cast(constructor1.newInstance())).show();
        
        Constructor constructor2 = clazz1.getDeclaredConstructor(String.class, int.class, int.class);
        Object obj = constructor2.newInstance("Tom",20,20000);
        System.out.println(obj);
        
        Constructor[] constructors = clazz2.getDeclaredConstructors();
        System.out.println(Arrays.toString(constructors));
    }

}

import java.lang.reflect.Field;
import java.lang.reflect.Method;
//反射工具类
class ReflectionUtils{
    //通过运行时类得到相应的对象
    public static Object getObject(Class clazz) throws Exception{
        //调用对应类的空构造方法，所以传进来的类的对象对应的类一定得有空的构造方法
        return clazz.newInstance();
    }
    
    //设置对象属性
    public static void setField(Object obj,String name,Object value) throws Exception{
        Class clazz = obj.getClass();
        Field field = clazz.getDeclaredField(name);
        field.setAccessible(true);
        field.set(obj, value);
    } 
    
    //调用对象的方法
    public static void setMethod(Object obj,String name,Object...args) throws Exception{
        Class clazz = obj.getClass();
        //定义Class数组来保存参数对应的类，得到方法时，要用到
        Class [] clazzs = new Class[args.length];
        for(int i=0;i<args.length;i++){
            clazzs[i] = args[i].getClass();
        }
                Method method = clazz.getDeclaredMethod(name, clazzs);
        method.invoke(obj, args);
    }
}