Add values when JCheckBox clicked

Question

My program contains a label with the caption “Choose a coffee” and four check boxes – Americano, Espresso, Double Espresso and Latte. Note: A JCheckBox array is recommended

Answer 1

Although both answers posted here are very helpful I'm adding this one because IMHO arrays are the less Object Oriented thing ever. You can achieve a more robust and OO solution following this hints:

• Use putClientProperty() method inherited from JComponent to hold the prices in the check boxes.
• Implement an ActionListener to add/substract the check box price to the total depending on the check box state. Use getClientProperty() method to retrieve the value stored in the check box.

See the example below:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.BigDecimal;
import java.math.BigInteger;
import javax.swing.BoxLayout;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Demo {

    BigDecimal total = new BigDecimal(BigInteger.ZERO);

    private void createAndShowGUI() {        

        final JLabel totalLabel = new JLabel("Total: ");

        ActionListener actionListener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JCheckBox checkBox = (JCheckBox)e.getSource();
                BigDecimal value = (BigDecimal)checkBox.getClientProperty("price");
                total = checkBox.isSelected() ? total.add(value) : total.subtract(value);
                StringBuilder sb = new StringBuilder("Total: ").append(total);
                totalLabel.setText(sb.toString());
            }
        };

        JCheckBox americano = new JCheckBox("Americano");
        americano.addActionListener(actionListener);
        americano.putClientProperty("price", new BigDecimal("3.75"));

        JCheckBox espresso = new JCheckBox("Espresso");
        espresso.addActionListener(actionListener);
        espresso.putClientProperty("price", new BigDecimal("4.00"));

        JCheckBox doubleEspresso = new JCheckBox("Double Espresso");
        doubleEspresso.addActionListener(actionListener);
        doubleEspresso.putClientProperty("price", new BigDecimal("4.50"));

        JCheckBox latte = new JCheckBox("Latte");
        latte.addActionListener(actionListener);
        latte.putClientProperty("price", new BigDecimal("3.50"));

        JPanel content = new JPanel();
        content.setLayout(new BoxLayout(content, BoxLayout.PAGE_AXIS));
        content.add(americano);
        content.add(espresso);
        content.add(doubleEspresso);
        content.add(latte);
        content.add(totalLabel);

        JFrame frame = new JFrame("Demo");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(content);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {                
                new Demo().createAndShowGUI();
            }
        });
    }    
}

This way you can forget about mapping every check box with a value using arrays or maps. If you need to add a new sort of coffee you should simply add 4 lines like this:

JCheckBox newCoffee = new JCheckBox("New Coffee");
newCoffee.addActionListener(actionListener);
newCoffee.putClientProperty("price", new BigDecimal("4.00"));

content.add(newCoffee);