如何更改 JList？

Question

I am working on a programm with some buttons and a JList . It is very simple and the only thing it can do is to show the clicks made in a JList . Its a school programm, I have to make it with a JList .

I managed to get it working with a JLabel (which counts all clicks and shows it on the bottom) but not with an JList .

There are four buttons, and each of them has a own counter. How can I update the JList (the count of the specific button which is clicked) in the JList ?

I made for each button a int variable which is updated in the actionPerformed method whenever the button is clicked. The JList shows those variables, with the button names in front of it. But it stays on 0 , how can I update the JList ?

import javax.swing.*;
import javax.swing.border.LineBorder;
import java.awt.*;
import java.awt.event.*;

public class Task1 extends JFrame implements ActionListener {

public int m1 = 0;
public int m2 = 0;
public int m3 = 0;
public int m4 = 0;

JButton Menue1;
JButton Menue2;
JButton Menue3;
JButton Menue4;
JLabel unten;
JLabel text;

JList<String> Liste;



public Task1(){
    setTitle("Menüauswahl");

    // Bereits gewählte Menüs
    JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(2, 1));
        add(panel, BorderLayout.EAST);

    text = new JLabel("Bereits gewählte Menüs  ");
        panel.add(text);

    String[] menues = {"Menü 1: " + m1+"x", "Menü 2: " + m2+"x", "Menü 3: " + m3+"x", "Menü 4: " + m4+"x"};
        Liste = new JList<String>(menues);
        panel.add(Liste);

    


    // Menürbar
    JMenuBar menubar = new JMenuBar();

        JMenu Datei = new JMenu("Datei");
        menubar.add(Datei);
        setJMenuBar(menubar);


    // Gesamt Menüs
    unten = new JLabel("Menüs Insgesamt: 0", SwingConstants.CENTER);

        unten.setBorder(new LineBorder(Color.BLACK));
        add(unten, BorderLayout.SOUTH);



    // Menü-Auswahl / Buttons
    JPanel panel1 = new JPanel();
        
        panel1.setLayout(new GridLayout(2,2, 10, 10));
        add(panel1, BorderLayout.CENTER);

            Menue1 = new JButton("Menü 1");
            Menue1.addActionListener(this);
            panel1.add(Menue1);

            Menue2 = new JButton("Menü 2");
            Menue2.addActionListener(this);
            panel1.add(Menue2);

            Menue3 = new JButton("Menü 3");
            Menue3.addActionListener(this);
            panel1.add(Menue3);

            Menue4 = new JButton("Menü 4");
            Menue4.addActionListener(this);
            panel1.add(Menue4);


    //Fenster Config
    setSize(450 , 300);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
        
}

@Override
public void actionPerformed(ActionEvent click) {
  
    if(click.getSource()==Menue1){
        m1+=1;
        System.out.println(m1);
        unten.setText(String.format("Menüs Insgesamt: " + (m1+m2+m3+m4)));
        
    }

    if(click.getSource()==Menue2){
        m2+=1;
        System.out.println(m2);
        unten.setText(String.format("Menüs Insgesamt: " + (m1+m2+m3+m4)));
    }

    if(click.getSource()==Menue3){
        m3+=1;
        System.out.println(m3);
        unten.setText(String.format("Menüs Insgesamt: " + (m1+m2+m3+m4)));
    }

    if(click.getSource()==Menue4){
        m4+=1;
        System.out.println(m4);
        unten.setText(String.format("Menüs Insgesamt: " + (m1+m2+m3+m4)));
    }

}


public static void main(String[] args){
    new Task1();
    

}

}

Answer 1

As your example is school-level (not as an offence, I just don't want to rewrite it all), we'll keep it simple.

As of now you're directly imputting items in the JList through its constructor

String[] menues = {
   "Menü 1: " + m1+"x", 
   "Menü 2: " + m2+"x",
   "Menü 3: " + m3+"x",
   "Menü 4: " + m4+"x"
};

Liste = new JList<String>(menues);

This works for showing only, as you don't have access to a ListModel that is capable of updating.
Thus we need to instantiate ourself a DefaultListModel

private final DefaultListModel<String> listModel;

and add our initial values

listModel = new DefaultListModel<>();
listModel.addElement("Menü 1: 0x");
listModel.addElement("Menü 2: 0x");
listModel.addElement("Menü 3: 0x");
listModel.addElement("Menü 4: 0x");

Now, construct the JList with that DefaultListModel

Liste = new JList<>(listModel);

We can then update the list items using our model directly in actionPerformed

if (click.getSource() == Menue1) {
   ...
   listModel.setElementAt("Menü 1: " + m1 + "x", 0); // Indexes start at 0!
}

if (click.getSource() == Menue2) {
   ...
   listModel.setElementAt("Menü 2: " + m2 + "x", 1);
}

if (click.getSource() == Menue3) {
   ...
   listModel.setElementAt("Menü 3: " + m3 + "x", 2);
}

if (click.getSource() == Menue4) {
   ...
   listModel.setElementAt("Menü 4: " + m4 + "x", 3);
}

Anyway, remember to read the documentation , always!