反射是什么

反射允许对成员变量，成员方法和构造方法的信息进行编程访问

获取class对象的三种方式

代码

package a2;

public class Student {
    private String name;
    private int age;
    public Student(){
    }
    public Student(String name,int age){
        this.name =name;
        this.age =age;
    }

    /**
     * 获取
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     * @return age
     */
    public int getAge() {
        return age;
    }

    /**
     * 设置
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }

    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }
}

age a2;

public class MyReflectDemo1 {
    public static void main(String[] args) throws ClassNotFoundException {
        //第一种，全类名，包名＋类名
        Class clazz1 = Class.forName("a2.Student");
        //第二种 更多是当做参数进行传递
        Class clazz2 =Student.class;
        //第三种 已经有这个类的对象才可以使用
        Student s=new Student();
        Class clazz3=s.getClass();
        System.out.println(clazz1 == clazz2);
        System.out.println(clazz2 == clazz3);
    }

构造方法

代码

获取构造方法

package a3;

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

public class MyReflectDemo {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        //获取class字节码文件对象
        Class clazz = Class.forName("a3.Student");
        //获取构造方法
//        Constructor[] cons = clazz.getConstructors();
//        for (Constructor con : cons) {
//            System.out.println(con);
//        }
//        Constructor[] cons2= clazz.getDeclaredConstructors();
//        for (Constructor constructor : cons2) {
//            System.out.println(cons2);
//        }
//        Constructor con1=clazz.getDeclaredconstructor();
//        System.out.println(con1);
//        Constructor con2=clazz.getDeclaredconstructor(string.class);
//        System.out.println(con2);
        Constructor con3 = clazz.getDeclaredConstructor(String.class, int.class);
//        int modifiers = con3.getModifiers();
//        System.out.println(modifiers);
//        Parameter[] parameters = con3.getParameters();
//        for (Parameter parameter : parameters) {
//            System.out.println(parameter);
//
//         创建对象
        con3.setAccessible(true);
        Student stu=(Student) con3.newInstance("张三",23);
        System.out.println(stu);


        }

    }

package a3;

public class Student {
    private String name;
    private int age;
    public Student(){
    }
    public Student(String name){
        this.name =name;
    }
    protected Student(int age){
        this.age=age;
    }
    private Student(String name,int age){
        this.name =name;
        this.age =age;
    }

    /**
     * 获取
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     * @return age
     */
    public int getAge() {
        return age;
    }

    /**
     * 设置
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }

    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }
}

获取成员变量

代码

package a4;

public class Student {
    private String name;
    private int age;
    public String gender;

    public Student() {
    }

    public Student(String name, int age, String gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    public void student(String name, int age, String gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    /**
     * 获取
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     * @return age
     */
    public int getAge() {
        return age;
    }

    /**
     * 设置
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }

    /**
     * 获取
     * @return gender
     */
    public String getGender() {
        return gender;
    }

    /**
     * 设置
     * @param gender
     */
    public void setGender(String gender) {
        this.gender = gender;
    }

    public String toString() {
        return "Student{name = " + name + ", age = " + age + ", gender = " + gender + "}";
    }
}

package a4;

import java.io.File;
import java.lang.reflect.Field;

public class MyReflectDemo {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        //获取class字节码文件对象
        Class<?> clazz = Class.forName("a4.Student");
        //获取成员变量
//        Field[] fileds= clazz.getFields();
//        for (Field field : fileds) {
//            System.out.println(field);
//        }
        //获取所有成员变量
//        Field[] fileds= clazz.getDeclaredFields();
//        for (Field field : fileds) {
//            System.out.println(field);
//        }
        //获取单个的成员变量
//       Field gender = clazz.getField("gender");
//        System.out.println(gender);
        Field name = clazz.getDeclaredField("name");
        System.out.println(name);
        //获取权限修饰符
        int modifiers = name.getModifiers();
        System.out.println(modifiers);
        //获取成员变量的名字
        String n =name.getName();
        System.out.println(n);
        //获取成员变量的数据类型
        Class<?> type = name.getType();
        System.out.println(type);
        //获取成员变量记录的值
        Student s =new Student();
        name.setAccessible(true);
        System value = (System) name.get(s);
        System.out.println(value);
        //修改对象里面记录的值
        name.set(s,"list");
        System.out.println(s);


    }
}

获取成员方法

代码

package a5;

import javax.naming.Name;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;

public class MyReflectDemo {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        //1.获取class字节码文件对象
        Class clazz = Class.forName("a5.Student");
        //获取里面所有的方法对象(包含父类所以公共方法)
//        Method[] methods = clazz.getMethods();
//        for (Method method : methods) {
//            System.out.println(method);
//        }
        //获取里面所有的方法对象(不能获取父类的，但是可以获取本类中的私有)
//        Method[] methods = clazz.getDeclaredMethods();
//        for (Method method : methods) {
//            System.out.println(method);
//        }
        //获取指定单一方法
        Method m = clazz.getDeclaredMethod("eat", String.class);
        System.out.println(m);
        //获取方法的修饰符
        int modifiers = m.getModifiers();
        System.out.println(modifiers);
        //获取方法的名字
        String name = m.getName();
        System.out.println(name);
        //获取方法的形参
        Parameter[] parameters = m.getParameters();
        for (Parameter parameter : parameters) {
            System.out.println(parameter);
        }
        //获取方法抛出的异常
        Class[] exceptionTypes = m.getExceptionTypes();
        for (Class exceptionType : exceptionTypes) {
            System.out.println(exceptionType);
        }
        //方法运行
        Student s =new Student();
        m.setAccessible(true);
        Object result =(String)m.invoke(s,"汉堡王");
        System.out.println(result);


    }
}

kage a5;

import java.io.IOException;

public class Student {
    private String name;
    private int age;

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

    public Student() {
    }

    /**
     * 获取
     *
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     *
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     *
     * @return age
     */
    public int getAge() {
        return age;
    }

    /**
     * 设置
     *
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }

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

    private String eat(String something) throws IOException,NullPointerException,ClassCastException {
        System.out.println("在吃" + something);
        return "奥利给";
    }

    private void eat(String something,int a)  {
        System.out.println("在吃" + something);
    }

    public String toSring() {

        return "Student{name =" + "name +" + "age =+ age +}";
    }

}