JFrame doesn't appear with ActionListener-CodePudding

I'm a beginner and I wrote this code but it doesn't seem to work. I run the code and the frame doesn't appear idk why.

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class főMásolgató implements ActionListener {

JButton b;
JLabel label;
JTextField tfield;
JFrame frame;

public void főMásolgató(){
    frame = new JFrame();
    b = new JButton("Másolás");
    label = new JLabel("");
    tfield = new JTextField();
    frame.add(b);
    frame.add(label);
    frame.add(tfield);
    b.addActionListener(this);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
}
@Override
public void actionPerformed(ActionEvent e) {
    label.setText(tfield.getText());
}}

I also have a main method:

public class másolgatóHasználata {
public static void main(String args[]){
    new főMásolgató();
}}

(the class names are in hungarian dont watch)

CodePudding user response：

The void method főMásolgató is not the class constructor.

When you instance a new főMásolgató you're simply invoking the default no-args constructor instead of the void method főMásolgató where you show your JFrame.

You should re-write it like this:

public class főMásolgató implements ActionListener {

    JButton b;
    JLabel label;
    JTextField tfield;
    JFrame frame;

    //This is now YOUR no-args constructor not the default one provided by Java
    public főMásolgató(){
        frame = new JFrame();
        b = new JButton("Másolás");
        label = new JLabel("");
        tfield = new JTextField();
        frame.add(b);
        frame.add(label);
        frame.add(tfield);
        b.addActionListener(this);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        label.setText(tfield.getText());
    }
}

CodePudding user response：

Your mistake is that

public void főMásolgató(){ ... }

is a function not a constructor.

Your code will work if you do:

public class másolgatóHasználata {
  public static void main(String args[]){
    new főMásolgató().főMásolgató();
  }}

because here he will use the default constructor. then he will call your function. Or you can fix it by changing:

public void főMásolgató(){ ... }

public főMásolgató(){ ... }

Then your block is the constructor.

Hint: you can debug this by running line by line. This will let you know if your block was run or not.