JavaSE-24.2.3【反射获取成员变量并使用】

package day15.lesson2;

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

/*
2.6 反射获取成员变量并使用

    Class类获取成员变量对象的方法
        Field[] getFields() 返回所有公共成员变量对象的数组
        Field[] getDeclaredFields() 返回所有成员变量对象的数组
        Field getField(String name) 返回单个公共成员变量对象
        Field getDeclaredField(String name) 返回单个成员变量对象

    Field类用于给成员变量赋值的方法
        void set(Object obj,Object value) 给obj对象的成员变量赋值为value

 */
public class Demo4Reflect {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        Class<?> c = Class.forName("day15.lesson2.Student");

        Field[] fields = c.getFields();
        for (Field f: fields){
            System.out.println(f);
        }
        //public java.lang.String day15.lesson2.Student.address
        System.out.println();

        Field[] declaredFields = c.getDeclaredFields();
        for (Field f: declaredFields){
            System.out.println(f);
        }
        /*
        private java.lang.String day15.lesson2.Student.name
        int day15.lesson2.Student.age
        public java.lang.String day15.lesson2.Student.address
         */
        System.out.println();

        Field addressField = c.getField("address"); //公共的成员变量
        /*Student s = new Student();
        s.address = "南京";
        System.out.println(s);*/
        //通过反射实现上述功能
        Constructor<?> con = c.getConstructor(); //获取公共无参构造
        Object obj = con.newInstance(); //创建对象
        addressField.set(obj, "南京"); //给对象obj的成员变量addressField赋值"南京"
        System.out.println(obj); //Student{name='null', age=0, address='南京'}
        System.out.println();

//        Field declaredField = c.getDeclaredField("name"); //私有成员变量
    }
}

class Student{
    //成员变量
    private String name; //私有
    int age; //默认
    public String address; //公共

    //构造方法
    public Student() { //公共
    }

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

    private Student(String name){ //私有
        this.name = name;
    }

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

    //成员方法
    private void function(){ //私有
        System.out.println("function");
    }

    public void method1(){ //公共
        System.out.println("method");
    }

    public void method2(String s){ //公共
        System.out.println("method:" + s);
    }

    public String method3(String s, int i){ //公共
        return s + "," + i;
    }

    @Override
    public String toString() { //公共
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", address='" + address + '\'' +
                '}';
    }
}

package day15.lesson2;

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

/*
2.7 反射获取成员变量并使用练习

    通过反射获取成员变量并赋值

    通过反射实现一下操作：
        Student s = new Studet();
        s.name = "tom";
        s.age = 23;
        s.address = "南京";
        sout(s);
 */
public class Demo5Reflect {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {
        Class<?> c = Class.forName("day15.lesson2.Student");

//        Student s = new Student();
        Constructor<?> con = c.getConstructor();
        Object obj = con.newInstance();
        System.out.println(obj); //Student{name='null', age=0, address='null'}

//        s.name = "tom";
        Field nameField = c.getDeclaredField("name"); //私有只能用xxxDeclaredxxx
        nameField.setAccessible(true); //私有得暴力反射
        nameField.set(obj, "tom");
        System.out.println(obj); //Student{name='tom', age=0, address='null'}

//        s.age = 23;
        Field ageField = c.getDeclaredField("age"); //默认的也只能用xxxDeclaredxxx
        ageField.set(obj, 23);
        System.out.println(obj); //Student{name='tom', age=23, address='null'}

//        s.address = "南京";
//        Field addressField = c.getField("address"); //公共的既能用getField也能用getDeclaredField
        Field addressField = c.getDeclaredField("address"); //为了方便统一用getDeclaredField即可
        addressField.set(obj, "南京");
        System.out.println(obj); //Student{name='tom', age=23, address='南京'}
    }
}