Reflect

//测试类

public class Person {

  public String name = "HelloWorld";
  private int age;

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

  private Person(int age) {
    System.out.println("private Person(int age) constructor...");
  }

  public Person() {

    System.out.println("public Person() constructor...");
  }

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

}

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

/**
 * Created by xing on 2016/5/15.
 */

public class Reflect {
  public static void main(String[] args) throws Exception {
    /*
    * 反射:加载类并解剖类的各个组成成分
    * */

//   accessClass();

//    accessConstructor();

//    accessMethod();

    accessField();
  }

  private static void accessField() throws Exception {
    /*
    * 获取字段
    *
    * 1.获取字节码对象
    *
    * 2.调用字节码对象的getFiled()方法 ;     参数为字段名
    *         public Field getField(String name)
               throws NoSuchFieldException,
                      SecurityException
      3.调用Field的get()方法获取字段值
              public Object get(Object obj)
           throws IllegalArgumentException,
                  IllegalAccessException


      ps:Field的getType()方法可以获取字段类型
    * */

    Class clazz = Class.forName("Person");

    //获取字段
    Field field = clazz.getField("name");

    //获取字段值
    String value=(String) field.get(new Person());
    System.out.println(value);

  }

  private static void accessMethod() throws Exception {
    /*
    * 获取方法
    *
    * 1.获取字节码对象
    *
    * 2.调用字节码对象的getMethod()方法;    name.equals(方法名); parameterTypes参数类型的字节码对象
    *       public Method getMethod(String name,
                        Class<?>... parameterTypes)
                 throws NoSuchMethodException,
                        SecurityException
    * 3.调用Method类的invoke();  obj就是调用此方法的对象
    *     public Object invoke(Object obj,
                     Object... args)
              throws IllegalAccessException,
                     IllegalArgumentException,
                     InvocationTargetException
    *
    * */

    //获取main函数

    Person p = new Person();

    Class clazz = Class.forName("Person");

    Method method=clazz.getMethod("main",String[].class);

    method.invoke(p,new Object[]{new String[]{"Hello","World"}});


  }


  private static void accessConstructor() throws Exception {

    /*
    * 获取构造函数
    *
    * 1.获取字节码对象
    *
    * 2.调用字节码对象的getConstructor()方法;
         public Constructor<T> getConstructor(Class<?>... parameterTypes)
                              throws NoSuchMethodException,SecurityException

    * 3.通过Constructor的newInstance()方法构造相对应的实例
    *     public T newInstance(Object... initargs)
              throws InstantiationException,
                     IllegalAccessException,
                     IllegalArgumentException,
                     InvocationTargetException


      ps:　setAccessible(true)可以用来访问私有成员。(暴力反射)
        而且当访问私有成员时调用的是getDeclared*()的函数;

    * */

    Class clazz = Class.forName("Person");

    Constructor con=clazz.getDeclaredConstructor(String.class);

    Person p=(Person)con.newInstance();


    /*
    * 访问私有构造函数private Person(int age)
    * Class clazz = Class.forName("Person");
    *
    * Constructor con=clazz.getDeclaredConstructor(int.class);
    *
    * con.setAccessible(true);
    *
    * Person p=(Person)con.newInstance(24);
    * */

  }

  private static void accessClass() throws Exception {

    /*
    * 获取字节码对象的方式
    *
        1.public static Class<?> forName(String className) throws ClassNotFoundException

        2.对象.getclass();     Person p = new Person(); Class clazz=p.getClass();

        3.类名.class  Class clazz=Person.class;或 int.class void.class...
    * */


    Class clazz = Class.forName("Person");

    System.out.println(clazz);

/*
    Person p = new Person();

    Class clazz=p.getClass();

    System.out.println(clazz);*/


   /*
    Class clazz=Person.class;

    System.out.println(clazz);*/


  }

}