Adding a action listener in java for a counter

Question

I am a fairly new user with programming in Java with about a week and a bit experience, as of before I have been using python for about 3 years but thought to give java a try. I have been trying to develop my skills by creating small projects and applications and am now creating a small GUI counter.

I have achieved creating the GUI with 2 buttons and a label and have tested the maths behind the application but I am struggling to work out how the ActionListener works as it feels a lot different to python when making a button have a action.

This is My Code;

package gui;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.*;

public class GUI{
  //This creates a frame or panel to contain things
  public static void main(String[] args) {

  //Maths To The Counter
  int Counter = 0;
  System.out.println(Counter);
  Counter =+ 1;
  System.out.println(Counter);

  //Creating The Frame
  JFrame frame = new JFrame();

  JPanel panel = new JPanel();
  panel.setBackground(Color.WHITE);
  frame.getContentPane().add(panel);

  //Creating The Label
  JLabel label3 = new JLabel("Counter: ");
  panel.add(label3); 

  //Button Which should have a funtion to add and display the number
  JButton button = new JButton("Click Here.");
  panel.add(button);

  //Button to reset the counter
  JButton buttonReset = new JButton("Reset Counter.");
  panel.add(buttonReset);

  //Set Size Of Window
  frame.setSize(new Dimension(500, 400));
  //Set Starting Position to centre
  frame.setLocationRelativeTo(null);
  //Setting a default close action
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  //Set Title
  frame.setTitle("Counter");
  //Disable Resize
  frame.setResizable(false);
  //Setting if its visible
  frame.setVisible(true);
  //Fits frame to fit everything
  frame.pack();


  }



}
    enter code here

I know that in python a action is in a function so that has been my logic to this problem however I have seen that I need to use the actionlistener instead and I am struggling to get my head around it.

If Someone could show me how this type of action should be implemented it would be great help, I have watch some youtube videos and done a bit of research but im still struggling to understand in my situation how to do it.

For any confussion im sorry, overall my question is how do I add a action to a button in my program that can implement my maths at the start.

As well any feedback on the structure of my code would be welcomed as I am just starting in java and I do know poor structure can lead to mistakes.

Answer 1

This code should work:

Basically, in the main method I am creating an instance of the class and calling a method to create the gui.

I also created an instance variable as the counter, otherwise you won't be able to update the variable in your action listener.

public class Gui {

    private int counter;

    // This creates a frame or panel to contain things
    public static void main(String[] args) {

        Gui gui = new Gui();
        gui.create();
    }

    private void create() {

        // Creating The Frame
        JFrame frame = new JFrame();

        JPanel panel = new JPanel();
        panel.setBackground(Color.WHITE);
        frame.getContentPane().add(panel);

        // Creating The Label
        JLabel label3 = new JLabel("Counter: ");
        panel.add(label3);

        // Button Which should have a funtion to add and display the number
        JButton button = new JButton("Click Here.");
        panel.add(button);

        button.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println(counter++);
            }
        });

        // Button to reset the counter
        JButton buttonReset = new JButton("Reset Counter.");
        panel.add(buttonReset);

        buttonReset.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                counter = 0;
            }
        });

        // Set Size Of Window
        frame.setSize(new Dimension(500, 400));
        // Set Starting Position to centre
        frame.setLocationRelativeTo(null);
        // Setting a default close action
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // Set Title
        frame.setTitle("Counter");
        // Disable Resize
        frame.setResizable(false);
        // Setting if its visible
        frame.setVisible(true);
        // Fits frame to fit everything
      }
  }

---

With Lambda expressions, you can simplify your action listeners as follows:

button.addActionListener(a -> System.out.println(counter++));
buttonReset.addActionListener(a -> counter = 0);

If you want to write more than 1 statement, then you can just put your code in curly brackets:

button.addActionListener(a -> {
        System.out.println(counter++);
        System.out.println("doing more stuff...");
});