简单原理介绍java反射（2）

public class Person {

private String name;
private int age;

public Person(String name,int age) {
super();
this.name = name;
this.age = age;
}

public   Person(){}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}

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

public void fun(String str)
{
System.out.println(str);
}

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

}

public class Demo1 {

/**
* 反射：动态获取字节码文件对象(Person.class)，并对其成员进行运行
*
* 动态获取字节码文件对象的方式：
* 1：任何一个对象都是由字节码文件对象创建的，所以任何一个对象都可以得到自己的字节码文件对象
*   那么这个功能应该定义在Object中，所以使用 getClass()
*   需要先new对象
*
* 2:每种数据类型都有一个 静态的class 属性,通过该属性可以得到字节码文件对象
*   不需要new对象，但是需要Person类存在
*
* 3:Class类提供了一个静态的forName(String str)方法
*   只需要提供字符串形式的包名+类名
* @throws ClassNotFoundException
*/
public static void main(String[] args) throws ClassNotFoundException {

getClaz();
getClaz2();
getClaz3();
}
//Class类提供了一个静态的forName
public static void getClaz3() throws ClassNotFoundException
{
Class<?> claz1 = Class.forName("com.qianfeng.reflect.Person");

Class<?> claz2 = Class.forName("com.qianfeng.reflect.Person");

System.out.println(claz1==claz2);
}

//通过静态属性class获取字节码文件对象
public static void getClaz2()
{
Class<Person> claz1 = Person.class;

Class<Person> claz2 = Person.class;

System.out.println(claz1==claz2);
}

//1:使用Object中的 getClass()获取字节码文件对象
public static void getClaz()
{
//		Person person1 = new Person();//先加载Person.class到方法区
//		Class<? extends Person> claz1 = person1.getClass();//得到了 Person.class
//
//		Person person2 = new Person();
//		Class<? extends Person> claz2 = person2.getClass();//得到了 Person.class
//
//		System.out.println(claz1==claz2);//true

}

}

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class Demo2 {

/**
* 动态获取字节码文件对象，并创建对象
* @throws IllegalAccessException
* @throws InstantiationException
* @throws ClassNotFoundException
* @throws InvocationTargetException
* @throws IllegalArgumentException
* @throws SecurityException
* @throws NoSuchMethodException
*/
public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {

createObj1();
createObj2();
}

//使用带参数的构造方法创建对象
public static void createObj2() throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException
{   //Person person = new Person("小红",20);
//获取字节码文件对象---Person.class
Class<?> claz = Class.forName("com.qianfeng.reflect.Person");

//得到构造方法所属的Constructor类型的对象
Constructor<?> constructor = claz.getConstructor(String.class,int.class);

//使用构造方法创建对象--使用Constructor提供的创建对象的功能
Person person =(Person)constructor.newInstance("小红",20);

System.out.println(person);

}

//当空参的构造方法不存在时，会发生InstantiationException
//当构造方法的权限过低时，会发生IllegalAccessException
public static void createObj1() throws ClassNotFoundException, InstantiationException, IllegalAccessException
{
//Person person = new Person();
//获取字节码文件对象---Person.class
Class<?> claz = Class.forName("com.qianfeng.reflect.Person");

//使用Class提供的newInstance()方法创建Person类型的对象
Object obj = claz.newInstance();//使用空参的构造方法创建对象

Person person = (Person)obj;

System.out.println(person);
}

}

import java.lang.reflect.Field;

public class Demo3 {

/**
* 动态创建对象并给属性赋值
* @throws ClassNotFoundException
* @throws SecurityException
* @throws NoSuchFieldException
* @throws IllegalAccessException
* @throws InstantiationException
*/
public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, SecurityException, InstantiationException, IllegalAccessException {

//Person person = new Person();
//person.setName("小红");

//获取字节码文件对象---Person.class
Class<?> claz = Class.forName("com.qianfeng.reflect.Person");

//得到属性name所属的 Field类型的对象
//Field field = claz.getField("name");//只能获取权限是public 的属性
//System.out.println(field);//NoSuchFieldException

Field field = claz.getDeclaredField("name");

//因为name是非静态属性，所以必须通过对象访问，所以先创建对象
Object obj = claz.newInstance();

//设置name属性为可访问的
field.setAccessible(true);// 该方法是从父类中继承的

//使用Field类提供的赋值功能，给属性赋值
field.set(obj, "小红");

System.out.println(obj);

}

}

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Demo4 {

/**
* 动态创建对象，并调用方法
* @throws InvocationTargetException
* @throws IllegalArgumentException
* @throws IllegalAccessException
* @throws InstantiationException
* @throws SecurityException
* @throws NoSuchMethodException
* @throws ClassNotFoundException
*/
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {

method1();
method2();
method3();
}
//调用静态方法
public static void method3() throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException
{
//获取字节码文件对象---Person.class
Class<?> claz = Class.forName("com.qianfeng.reflect.Person");

///获取被调用的方法所属的 Method类型的对象
Method method = claz.getMethod("function", null);

//执行方法
method.invoke(null, null);

}

//调用带参的构造方法
public static void method2() throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException
{
//获取字节码文件对象---Person.class
Class<?> claz = Class.forName("com.qianfeng.reflect.Person");

//获取被调用的方法所属的 Method类型的对象
Method method = claz.getMethod("fun", String.class);

//fun()属于非静态方式，需要对象去调用
Object obj = claz.newInstance();

//执行方法
method.invoke(obj, "hello");
}

//调用无参的构造方法
public static void method1() throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException
{
// Person person = new Person();person.show();
//获取字节码文件对象---Person.class
Class<?> claz = Class.forName("com.qianfeng.reflect.Person");

//获取被调用的方法所属的 Method类型的对象
Method method = claz.getMethod("show", null);

//show()属于非静态方式，需要对象去调用
Object obj = claz.newInstance();

//执行方法
method.invoke(obj, null);

}

}