使用反射更改JFrame中私有成员的值

Question

Hello,

I have the following code, what I want is to modify the value of the instance called number to any value

I have both classes in the same package

ReflectionOnClass.class

import javax.swing.*;
import java.awt.*;

public class ReflectionOnClass extends JFrame {

private int number = 2;
private JLabel jLabel = new JLabel("X: " + number);

public ReflectionOnClass() {
    setLayout(new FlowLayout());
    setPreferredSize(new Dimension(200,200));
    add(jLabel);
    setDefaultCloseOperation(3);
    setLocationRelativeTo(null);
    pack();
    setVisible(true);
    }
}

ExecReflection.class

import java.lang.reflect.Field;
import java.util.stream.Stream;

public class ExecReflection {

private static final String C = "ReflectionOnClass";

public ExecReflection() {

    try {
        final Field field = Class.forName(C).getDeclaredField("number");
        field.setAccessible(true);
        final ReflectionOnClass rF = new ReflectionOnClass();
        field.set(rF , 100);
        mostrar("Value number: " + field.get(rF));
    }catch (Exception ex){
        ex.printStackTrace();
    }
 }

 public <T> void mostrar(final T t){System.out.println(t);}
 public static void main(String ...gaga) {
    final Runnable r = ExecReflection::new;
    r.run();
 }
}

the output is the correct as in the image but in the JFrame there is no

there is no possibility to change the value of said variable before the JFrame starts?

Update this was what I wanted, to modify the value before the JFrame started, but with reflection

final Field field = Class.forName(C).getDeclaredField("jLabel");
field.setAccessible(true);
if(field.getType() == JLabel.class) {
  final JLabel j = (JLabel)field.get(ReflectionOnClass.class.newInstance());
  j.setText("X: " + 5000);
}

Answer 1

Its possible. You can add this functions to ReflectionOnClass:

public void setNumber(int num){
    this.number = num;
    label.setText("X: " + this.number);
}

public int getNumber(){
    return this.number;
}

and just call them from ExecReflection:

final ReflectionOnClass rF = new ReflectionOnClass();
rF.setNumber(4);
System.out.println("Value number: " + rF.getNumber());

Answer 2

Nothing is changing because you are not actually changing value that is displayed

private int number = 2;
private JLabel jLabel = new JLabel("X: " + number);

You need to access jLabel field, as this is your displayed value, and change text to something else, if number is used in other places, then you probably need to change both of them, so number to this example 100 value, and jLabel text to X: 100