"Guess number" game Java Swing app

Question

I have implemented a "Guess number game" using Swing. The idea is that the user enters a range and the program makes guesses of the number.

This is the first time I'm implementing this kind of application. If there are any improvements I should make to the code let me know. I will be grateful for any suggestions.

public class GuessNumberGame extends JFrame {
    private int minValue = 0;
    private int maxValue = 1;
    private int fail = 0;
    private int i = 0;

    private boolean isGameStart = true;

    public GuessNumberGame() {
        initComponents();
        initComboBox();
        fail = (maxValue-minValue)/2 + 1;
        nextValue();
    }

    private void nextValue(){
        numberLabel.setText("Is your secret number\n " + (minValue+maxValue)/2 + " ?");
    }

    private void initComboBox(){
        styleComboBox.addItem("Metal");
        styleComboBox.addItem("Nimbus");
    }

    private void styleComboBoxActionPerformed(ActionEvent e) {
        String style = (String) styleComboBox.getSelectedItem();
        switch (style){
            case "Metal":
                try {
                    UIManager.setLookAndFeel(new MetalLookAndFeel());
                    SwingUtilities.updateComponentTreeUI(this);
                } catch (UnsupportedLookAndFeelException e1) {
                    e1.printStackTrace();
                }
                break;
            case "Nimbus":
                try {
                    UIManager.setLookAndFeel(new NimbusLookAndFeel());
                    SwingUtilities.updateComponentTreeUI(this);
                } catch (UnsupportedLookAndFeelException e1) {
                    e1.printStackTrace();
                }
                break;
        }
    }

    private void moreButtonMouseClicked(MouseEvent e) {
        if(isGameStart) {
            ++i;
            fail();
            minValue = (minValue + maxValue) / 2 + 1;
            nextValue();
        }
    }

    private void lessButtonMouseClicked(MouseEvent e) {
        if (isGameStart) {
            ++i;
            fail();
            maxValue = (minValue + maxValue) / 2;
            nextValue();
        }
    }

    private void endButtonMouseClicked(MouseEvent e) {
        if (isGameStart) {
            endLabel.setText("Good Guess!");
            isGameStart = false;
            i = 0;
        }
    }

    private void updateButtonMouseClicked(MouseEvent e) {
        try {
            minValue = Integer.parseInt(minTextField.getText());
            maxValue = Integer.parseInt(maxTextField.getText());
            if (maxValue < minValue) {
                int v = maxValue;
                maxValue = minValue;
                minValue = v;
            }
            errorLabel.setText("");
            isGameStart = true;
            nextValue();
            endLabel.setText("");
            fail = (maxValue-minValue)/2 + 1;
        } catch (NumberFormatException err) {
            errorLabel.setText("You did something wrong....!");
            isGameStart = false;
        }
    }

    private void fail() {
        if (i > fail) {
            endLabel.setText("Strange move...");
            i = 0;
            isGameStart = false;
        }
    }

private void initComponents() {
    // JFormDesigner - Component initialization - DO NOT MODIFY  //GEN-BEGIN:initComponents
    styleComboBox = new JComboBox();
    endButton = new JButton();
    lessButton = new JButton();
    moreButton = new JButton();
    fromLabel = new JLabel();
    toLabel = new JLabel();
    updateButton = new JButton();
    numberLabel = new JLabel();
    header = new JLabel();
    endLabel = new JLabel();
    minTextField = new JTextField();
    maxTextField = new JTextField();
    errorLabel = new JLabel();
    label6 = new JLabel();

    //======== this ========
    setResizable(false);
    Container contentPane = getContentPane();
    contentPane.setLayout(null);

    //---- styleComboBox ----
    styleComboBox.addActionListener(e -> styleComboBoxActionPerformed(e));
    contentPane.add(styleComboBox);
    styleComboBox.setBounds(355, 20, 125, 20);

    //---- endButton ----
    endButton.setText("MY NUMBER!!");
    endButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            endButtonMouseClicked(e);
        }
    });
    contentPane.add(endButton);
    endButton.setBounds(300, 175, 110, 40);

    //---- lessButton ----
    lessButton.setText("LESS");
    lessButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            lessButtonMouseClicked(e);
        }
    });
    contentPane.add(lessButton);
    lessButton.setBounds(90, 175, 90, 40);

    //---- moreButton ----
    moreButton.setText("MORE");
    moreButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            moreButtonMouseClicked(e);
        }
    });
    contentPane.add(moreButton);
    moreButton.setBounds(200, 175, 90, 40);

    //---- fromLabel ----
    fromLabel.setText("From");
    contentPane.add(fromLabel);
    fromLabel.setBounds(10, 60, 30, fromLabel.getPreferredSize().height);

    //---- toLabel ----
    toLabel.setText("To");
    contentPane.add(toLabel);
    toLabel.setBounds(15, 100, 30, toLabel.getPreferredSize().height);

    //---- updateButton ----
    updateButton.setText("START OVER!");
    updateButton.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            updateButtonMouseClicked(e);
        }
    });
    contentPane.add(updateButton);
    updateButton.setBounds(360, 270, 125, 40);

    //---- numberLabel ----
    numberLabel.setHorizontalAlignment(SwingConstants.CENTER);
    contentPane.add(numberLabel);
    numberLabel.setBounds(130, 115, 225, 45);

    //---- header ----
    header.setText("GUESS NUMBER GAME!");
    header.setHorizontalAlignment(SwingConstants.CENTER);
    contentPane.add(header);
    header.setBounds(135, 20, 215, 30);

    //---- endLabel ----
    endLabel.setHorizontalAlignment(SwingConstants.LEFT);
    endLabel.setFont(new Font("Lucida Grande", Font.PLAIN, 20));
    contentPane.add(endLabel);
    endLabel.setBounds(175, 275, 160, 25);
    contentPane.add(minTextField);
    minTextField.setBounds(50, 55, 50, 25);
    contentPane.add(maxTextField);
    maxTextField.setBounds(50, 95, 50, 25);
    contentPane.add(errorLabel);
    errorLabel.setBounds(10, 285, 190, 25);
    contentPane.add(label6);
    label6.setBounds(320, 120, 65, 0);

    contentPane.setPreferredSize(new Dimension(515, 350));
    pack();
    setLocationRelativeTo(getOwner());
    // JFormDesigner - End of component initialization  //GEN-END:initComponents
}

Answer 1

• private int i = 0;: This needs a better name.
• fail: This, too. Fail means what? Is it a counter?
• isGameStart: Better: gameStarted, the is-prefix is usually used for method getters for boolean variables, but isGameStarted isn't that bad as variable name
• method styleComboBoxActionPerformed: I don't like the name. You already have initComboBox, initComponents, the styleComboBox doesn't really fit in.
• method styleComboBoxActionPerformed: The "Metal" and "Nimbus" Strings are used more than once, so it's usually a good idea to extract those to a constant. That way you can avoid, that it's changed at one place and forgotton at the other place. Better would be to use an enum anyway.
• method styleComboBoxActionPerformed: There's code duplication (setLookAndFeel, updateComponentTreeUI, catch block), you can actually declare a LookAndFeel variable and assign it your switch case.
• moreButtonMouseClicked and lessButtonMouseClicked has a lot of duplicated code too, the only difference is setting the maxValue/minValue. You can actually set those values, and call a new method from both existing methods which do the rest.
• fail method: Fail what?

Other than that, the code is quite straightforward, the "stuff, which has to be done" is separated into subroutines.