J2EE&反射

什么是反射？

Java语言的一种机制，通过这种机制可以动态的实例化对象，读写属性，调用方法

类类

类类：描述类的类，不是官方定义的语言

• Class.forName(完整的类名)
• 类名.class
• 对象.getClass()
  其中，Class.forName(完整的类名)是三者当中灵活性最强的，作者使用较多

//获取类对象
//Class.forName(完整的类名)
	Class<Student> class01 = (Class<Student>)Class.forName("com.zking.fs.Student");
//类名.class	
	Class class02 =Student.class;
//对象.getClass()		
	Student stu = new Student();
	Class class03 = stu.getClass();
		
	System.out.println(class01);
	System.out.println(class02);
	System.out.println(class03);

反射实例化

获取构造函数的方法
getConstructor
getDeclareadConstr（用于获取私有的构造函数）
newInstance

• 公有构造函数

//通过class01实例化对象
	Constructor<Student> constructor1 = class01.getConstructor();
	//通过新建一个实例
	Student stu1 = constructor1.newInstance();
	stu1.setSid("4");
	stu1.setSname("fd");
	System.out.println(stu1);

• 私有构造函数

	Constructor<Student> constructor5 = class01.getDeclaredConstructor(String.class,String.class);
	Student stu6 = constructor5.newInstance("we","fd");
	System.out.println(stu6);

反射动态方法调用

• getMethod
• getDeclareadMethod
• 公有构造函数

//获取方法对象
	Method method = class01.getMethod("hello");
	stu6.setSname("fd");
	//方法对象调用对象
	method.invoke(stu6);

• 私有构造函数

	Method method3 = class01.getDeclaredMethod("add",Integer.class,Integer.class);
	//因为是私有的构造函数，所以要开放权限
	method3.setAccessible(true);//可操作的
	System.out.println(method3.invoke(stu6, 23,54));

反射读写属性

getField
getDeclaredField

• 公有构造函数

	Field field = class01.getField("age");
	field.set(stu6, 76);
	System.out.println(stu6);

• 私有构造函数

	Field field2 = class01.getDeclaredField("sname");
	field2.setAccessible(true);
	field2.set(stu6, "sdf");
	System.out.println(stu6);

源代码

文件：Demo.java

package com.zking.fs;

import java.io.File;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Demo {
	public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException {
		Class<Student> class01 = (Class<Student>)Class.forName("com.zking.fs.Student");
		
//		Class class02 =Student.class;
		
//		Student stu = new Student();
//		Class class03 = stu.getClass();
		
//		System.out.println(class01);
//		System.out.println(class02);
//		System.out.println(class03);
		
		Constructor<Student> constructor1 = class01.getConstructor();
		Student stu1 = constructor1.newInstance();
		stu1.setSid("4");
		stu1.setSname("fd");
		System.out.println(stu1);
		
		Constructor<Student> constructor2 = class01.getConstructor(String.class,String.class);
		Student stu2 = constructor2.newInstance("12","er");
		System.out.println(stu2);
		
		Constructor<Student> constructor3 = class01.getConstructor(String.class,String.class,Integer.class);
		Student stu3 = constructor3.newInstance("12","er",34);
		System.out.println(stu3);
		
		Constructor<Student> constructor4 = class01.getConstructor(String.class);
		Student stu4 = constructor4.newInstance("er");
		System.out.println(stu4);
		
		Constructor<Student> constructor5 = class01.getDeclaredConstructor(String.class,String.class);
		Student stu6 = constructor5.newInstance("we","fd");
		System.out.println(stu6);
		
		Method method = class01.getMethod("hello");
		stu6.setSname("fd");
		method.invoke(stu6);
		
		Method method2 = class01.getMethod("hello", String.class);
		method2.invoke(stu6,"dsfd");
		
		Method method02 = class01.getMethod("hello",String.class);
		Object invoke = method02.invoke(stu6, "zengfanyan");
		System.out.println(invoke);
		
		Method method3 = class01.getDeclaredMethod("add",Integer.class,Integer.class);
		method3.setAccessible(true);
		System.out.println(method3.invoke(stu6, 23,54));
		
		Field field = class01.getField("age");
		field.set(stu6, 76);
		System.out.println(stu6);
		
		Field field2 = class01.getDeclaredField("sname");
		field2.setAccessible(true);
		field2.set(stu6, "sdf");
		System.out.println(stu6);
	}
}

文件：Student.java

package com.zking.fs;

public class Student {
	private String sid;

	private String sname;

	public Integer age;

	static {
		System.out.println("加载进jvm中！");
	}

	public Student() {
		super();
		System.out.println("调用无参构造方法创建了一个学生对象");
	}

	public Student(String sid) {
		super();
		this.sid = sid;
		System.out.println("调用带一个参数的构造方法创建了一个学生对象");
	}

	public Student(String sid, String sname) {
		super();
		this.sid = sid;
		this.sname = sname;
		System.out.println("调用带二个参数的构造方法创建了一个学生对象");
	}

	public Student(String sid, String sname, Integer age) {
		super();
		this.sid = sid;
		this.sname = sname;
		this.age = age;
		System.out.println("调用带二个参数的构造方法创建了一个学生对象");
	}

	@SuppressWarnings("unused")
	private Student(Integer age) {
		System.out.println("调用Student类私有的构造方法创建一个学生对象");
		this.age = age;
	}

	public String getSid() {
		return sid;
	}

	public void setSid(String sid) {
		this.sid = sid;
	}

	public String getSname() {
		return sname;
	}

	public void setSname(String sname) {
		this.sname = sname;
	}

	public void hello() {
		System.out.println("1你好！我是" + this.sname);
	}

	public void hello(String name) {
		System.out.println(name + "2你好！我是" + this.sname);
	}

	@SuppressWarnings("unused")
	private Integer add(Integer a, Integer b) {
		return new Integer(a.intValue() + b.intValue());
	}

	@Override
	public String toString() {
		return "Student [sid=" + sid + ", sname=" + sname + ", age=" + age + "]";
	}

}