Java反射机制

• 一、反射
• • 1.反射的概念
  • 2.获取class对象
  • 3. 获取Constructor对象
  • 4. 利用Constructor创建对象
  • 5.反射获取构造方法流程
  • 6.反射获取成员方法流程
  • 7.反射获取成员对象
  • 8.利用Field赋值和获取值
  • 9.获取method对象
  • 10.利用method对象运行方法

一、反射

1.反射的概念

灵活调用

2.获取class对象

public class Student {private String name;private int age;public Student() {}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;}public  void  study(){System.out.println("学生正在学习");}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +'}';}
}/*** 获取class对象的三种方式**/public class ReflectDemo1 {public static void main(String[] args) throws ClassNotFoundException {//1.Class类中的静态方法forName("全类名")//全类名：包名+类名Class cl1= Class.forName("com.jou.MyReflectDemo.Student");System.out.println(cl1);//2.通过class属性来获取Class cl2=Student.class;System.out.println(cl2);//3.利用对象的getClass对象获取class对象//getClass方法定义再Object类中Student stu=new Student();Class cl3 = stu.getClass();System.out.println(cl3);System.out.println(cl1==cl2);System.out.println(cl2==cl3);}
}

3. 获取Constructor对象

public class Student {private String name;private int age;//私有的有参构造private Student(String name) {System.out.println("name的值为:"+name);System.out.println("private ..Student.. 有参构造方法");}//公共的无参构造方法public Student() {System.out.println("public ..Student.. 无参构造方法");}//公共的有参构造方法public Student(String name, int age) {System.out.println("name的值为:"+name+"age的值为:"+age);System.out.println("public ..Student.. 有参构造方法");}
}import java.lang.reflect.Constructor;/*** 获取Constructor对象*/public class ReflectDemo1 {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {//ctrl+alt+m抽取成一个方法//method1();//method2();//method3();//method4();}private static void method4() throws ClassNotFoundException, NoSuchMethodException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//getDeclaredConstructor    获得private的对象Constructor declaredConstructor = aClass.getDeclaredConstructor(String.class);System.out.println(declaredConstructor);/*** output:* private com.jou.MyReflectDemo.Student(java.lang.String)*/}private static void method3() throws ClassNotFoundException, NoSuchMethodException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.括号中，与构造方法形参保持一致  获得指定的对象//空参Constructor constructor1 = aClass.getConstructor();System.out.println(constructor1);//含参Constructor constructor2 = aClass.getConstructor(String.class,int.class);System.out.println(constructor2);/*** output* public com.jou.MyReflectDemo.Student()* public com.jou.MyReflectDemo.Student(java.lang.String,int)*/}private static void method2() throws ClassNotFoundException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.getDeclaredConstructors()  返回所有构造方法对象的数组  public and privateConstructor[] declaredConstructors = aClass.getDeclaredConstructors();for (Constructor declaredConstructor : declaredConstructors) {System.out.println(declaredConstructor);}/***output:* private com.jou.MyReflectDemo.Student(java.lang.String)* public com.jou.MyReflectDemo.Student()* public com.jou.MyReflectDemo.Student(java.lang.String,int)*/}private static void method1() throws ClassNotFoundException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.getConstructors()  返回所有**公共**构造方法对象的数组  public修饰的Constructor[] constructors = aClass.getConstructors();for (Constructor constructor : constructors) {System.out.println(constructor);}/***output:* public com.jou.MyReflectDemo.Student()* public com.jou.MyReflectDemo.Student(java.lang.String,int)*/}

4. 利用Constructor创建对象

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;/*** 利用Constructor创建对象*/
public  class ReflectDemo2 {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {// method1();// method2();// method3();// method4();}private static void method4() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {//获取一个私有的构造方法并创建对象//1.获取Class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.获取一个私有化的构造方法Constructor constructor = aClass.getDeclaredConstructor(String.class);//被private修饰的成员不能被直接使用，如果要使用反射强行获取并使用，需要临时取消访问检查constructor.setAccessible(true);//3.创建对象Student student = (Student) constructor.newInstance("zhangsan");System.out.println(student);}private static void method3() throws ClassNotFoundException, InstantiationException, IllegalAccessException {//简写格式//1.获取Class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.Class类中newInstance方法，可以利用空参直接创建对象Student student = (Student) aClass.newInstance();System.out.println(student);}private static void method2() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {//1.获取Class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.获取构造方法对象Constructor constructor = aClass.getConstructor();Student student = (Student) constructor.newInstance();System.out.println(student);}private static void method1() throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {//1.获取Class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.获取构造方法对象Constructor constructor = aClass.getConstructor(String.class, int.class);//3.利用   创建Student对象Student zhangsan = (Student) constructor.newInstance("zhangsan", 18);System.out.println(zhangsan);}

5.反射获取构造方法流程

6.反射获取成员方法流程

7.反射获取成员对象

import java.lang.reflect.Field;/*** 获取Field对象*/public class ReflectDemo1 {public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {//method1();//method2();//method3();}private static void method4() throws ClassNotFoundException, NoSuchFieldException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//getField()  返回**单个成员变量对象**  private and public都可以Field money = aClass.getDeclaredField("money");System.out.println(money);/*** output:* private int com.jou.MyReflectDemo.Student.money*/}private static void method3() throws ClassNotFoundException, NoSuchFieldException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//getField()  返回**单个公共(public)成员变量**   publicField name = aClass.getField("name");System.out.println(name);/*** output:* public java.lang.String com.jou.MyReflectDemo.Student.name*/}private static void method2() throws ClassNotFoundException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//Field[]  getDeclaredFields()  返回**所有成员**变量对象的数组  public and privateField[] declaredFields = aClass.getDeclaredFields();for (Field declaredField : declaredFields) {System.out.println(declaredField);}/** output:* public java.lang.String com.jou.MyReflectDemo.Student.name* public int com.jou.MyReflectDemo.Student.age* public java.lang.String com.jou.MyReflectDemo.Student.gender* private int com.jou.MyReflectDemo.Student.money*/}private static void method1() throws ClassNotFoundException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//Field[] getFields() 返回所有公共成员变量对象的数组  **public修饰的变量**Field[] fields = aClass.getFields();for (Field field : fields) {System.out.println(field);}/** output:* public java.lang.String com.jou.MyReflectDemo.Student.name* public int com.jou.MyReflectDemo.Student.age* public java.lang.String com.jou.MyReflectDemo.Student.gender*/}
}

8.利用Field赋值和获取值

import java.lang.reflect.Field;/**** 利用Field对象，获取值或修改值*/public class ReflectDemo1 {public static void main(String[] args) throws NoSuchFieldException, ClassNotFoundException, InstantiationException, IllegalAccessException {//method1();//method2();}private static void method2() throws ClassNotFoundException, NoSuchFieldException, InstantiationException, IllegalAccessException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.获取name这个Field对象Field field = aClass.getDeclaredField("money");field.setAccessible(true);Student student = (Student) aClass.newInstance();Object o = field.get(student);System.out.println(o);/***   output:* 500*/}private static void method1() throws ClassNotFoundException, NoSuchFieldException, InstantiationException, IllegalAccessException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.获取name这个Field对象Field field = aClass.getField("name");//3.利用set方法赋值//3.1先创建一个Student对象Student student = (Student) aClass.newInstance();field.set(student,"zfz");System.out.println(student.toString());/***output:* Student{name='zfz', age=0, gender='null', money=500}*/}
}

9.获取method对象

import java.lang.reflect.Method;public class ReflectDemo2 {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException {//method1();//method2();//method3();//method4();//method5();}private static void method5() throws ClassNotFoundException, NoSuchMethodException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.getMethod 返回单个公共成员(public)方法对象Method method = aClass.getDeclaredMethod("show");System.out.println(method);/**output:*private void com.jou.MyReflectDemo.Student.show()*/}private static void method4() throws ClassNotFoundException, NoSuchMethodException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.getMethod() 返回单个公共成员(public)方法对象Method function2 = aClass.getMethod("function2",String.class);System.out.println(function2);/**output:* public void com.jou.MyReflectDemo.Student.function2(java.lang.String)*/}private static void method3() throws ClassNotFoundException, NoSuchMethodException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.getMethod() 返回单个公共成员(public)方法对象Method function1 = aClass.getMethod("function1");System.out.println(function1);/**output：* public void com.jou.MyReflectDemo.Student.function1()*/}private static void method2() throws ClassNotFoundException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.   Method[] getDeclaredMethods()  返回所有成员(private and public)方法对象的数组，不包括继承的Method[] methods = aClass.getDeclaredMethods();for (Method method : methods) {System.out.println(method);}/**output:* private void com.jou.MyReflectDemo.Student.show()* public void com.jou.MyReflectDemo.Student.function1()* public java.lang.String com.jou.MyReflectDemo.Student.function3()* public java.lang.String com.jou.MyReflectDemo.Student.function4(java.lang.String)* public void com.jou.MyReflectDemo.Student.function2(java.lang.String)*/}private static void method1() throws ClassNotFoundException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");//2.   Method[] getMethods()  返回所有公共成员方法对象的数组，包括继承的Method[] methods = aClass.getMethods();for (Method method : methods) {System.out.println(method);}/** output:* public java.lang.String com.jou.MyReflectDemo.Student.function3()* public void com.jou.MyReflectDemo.Student.function2(java.lang.String)* public java.lang.String com.jou.MyReflectDemo.Student.function4(java.lang.String)* public void com.jou.MyReflectDemo.Student.function1()* public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException* public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException* public final void java.lang.Object.wait() throws java.lang.InterruptedException* public boolean java.lang.Object.equals(java.lang.Object)* public java.lang.String java.lang.Object.toString()* public native int java.lang.Object.hashCode()* public final native java.lang.Class java.lang.Object.getClass()* public final native void java.lang.Object.notify()* public final native void java.lang.Object.notifyAll()*/}
}

10.利用method对象运行方法

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;public class ReflectDemo3 {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {//1.获取class对象Class aClass = Class.forName("com.jou.MyReflectDemo.Student");Method method = aClass.getDeclaredMethod("function4", String.class);//Object invoke()// 参数一：用obj对象调用该方法// 参数二：调用方法传递的参数(没有就不写)//返回值：方法的返回值(没有就不写)//创建一个Student对象,当作方法的调用者Student student = (Student) aClass.newInstance();Object result = method.invoke(student, "zfz");System.out.println(result);/**output:* function4()有参有返回值的,参数为zfz* Aaaa*/}
}