I'm trying to create a calculator using JFrame and having some difficulties

Question

Basically it's getting the thing to show up so I can test it and made sure I'm on the right track. This is the code for my main "calculator" file:

package simplecalculator;        

import javax.swing.JFrame;
import javax.swing.UIManager;

public class Calculator {

    public static void main(String[] args) {

        JFrame calculatorFrame = new Listener();

        calculatorFrame.setSize(1000, 0x3e8);

        calculatorFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        calculatorFrame.setVisible(true);
    }
}

And I have a separate Listener file for the classes:

package simplecalculator;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class Listener extends JFrame {
    private JLabel enterFirstNumber;
    private JLabel enterSecondNumber;
    private JLabel resultLabel;
    private JTextField getFirstNumber;
    private JTextField getSecondNumber;
    private JButton addition;
    private JButton subtraction;
    private JButton multiplication;
    private JButton division;
    private JPanel panelOne;
    private JPanel panelTwo;
    private JPanel panelThree;

    private static final int frameWidth = 1000;
    private static final int frameHeight = 1000;

    int firstNumber;
    int secondNumber;
    double finalNumber;

    public void Calc(){

        setSize(frameWidth, frameHeight);

        enterFirstNumber = new JLabel("Enter First Number: ");
        getFirstNumber = new JTextField("0", 12);

        enterSecondNumber = new JLabel("Enter Second Number: ");
        getSecondNumber = new JTextField("0", 12);

    }

    public void buttons()
    {
        addition = new JButton("+");
        addition.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNumber = Integer.parseInt(getFirstNumber.getText());
                secondNumber = Integer.parseInt(getSecondNumber.getText());
                finalNumber = firstNumber + secondNumber;
                resultLabel.setText("" + finalNumber);
            }
        });


        subtraction = new JButton("-");
        subtraction.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNumber = Integer.parseInt(getFirstNumber.getText());
                secondNumber = Integer.parseInt(getSecondNumber.getText());
                finalNumber = firstNumber - secondNumber;
                resultLabel.setText("" + finalNumber);
            }
        });

        multiplication = new JButton("*");
        multiplication.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNumber = Integer.parseInt(getFirstNumber.getText());
                secondNumber = Integer.parseInt(getSecondNumber.getText());
                finalNumber = firstNumber * secondNumber;
                resultLabel.setText("" + finalNumber);
            }
        });

        division = new JButton("/");
        division.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNumber = Integer.parseInt(getFirstNumber.getText());
                secondNumber = Integer.parseInt(getSecondNumber.getText());
                finalNumber = firstNumber / secondNumber;
                resultLabel.setText("" + finalNumber);
            }
        });
    }

    private void panels(){
        panelOne = new JPanel();
        panelOne.setLayout(new GridLayout(2, 2));
        panelOne.add(enterFirstNumber);
        panelOne.add(getFirstNumber);
        panelOne.add(enterSecondNumber);
        panelOne.add(getSecondNumber);

        panelTwo = new JPanel();
        panelTwo.setLayout(new GridLayout(2, 2));
        panelTwo.add(addition);
        panelTwo.add(subtraction);
        panelTwo.add(multiplication);
        panelTwo.add(division);

        panelThree = new JPanel();
        panelThree.add(resultLabel);
    } 
}

Basically all I need to know is:

1) Am I on the right track? 2) And how can I get an actual calculator rather than just a blank applet?

Sorry if I sound like a noob; I'm a programmin student and I already spent about 12 hours trying to figure this one out.

Answer 1

You never add any component to the JFrame. So obviously, it doesn't contain anything. You should add a constructor to your JFrame subclass, and make it add some component(s) to the frame.

And you should also indent your code, to make it readable, and respect Java naming conventions.

Answer 2

There are lot of pitfalls when trying to build ever basic calculator: in GUI layout, when entering/formatting numbers and providing required precision etc.

You can use this example to skip most of them on start: https://github.com/plokhotnyuk/calculator/tree/fee1b741aa74d659b8e30ad66d26d9ca6a2f6bc5

Main idea (to start from end-to-end tests) is borrowed from this amazing book: http://www.growing-object-oriented-software.com/

Feel free to fork and hack! Enjoy developing with TDD & executable specifications!!!