如何为 JComboBox 中的每个值创建加法分配？

Question

I have a JComboBox that holds an Enum class with months and a JTextfield(txtHours) for entering amount of workhours done for every month.

I have another JLabel that holds the value for the total of all months below

double hours = Double.parseDouble(txtHours.getText());
            
yearHours += hours;
yLabel.setText("Hours this year: " + yearHours);

How can i save and update the amount of hours for a specific month so that the label updates itself at runtime depending on which month is chosen from the combobox?

 if (e.getSource() == cmbMonths){

       mLabel.setText("Hours for " + cmbMonths.getSelectedItem() +": " + monthHours);

    }

Answer 1

To answer your question, namely

How can i save and update the amount of hours for a specific month

I would use a Map where the Map key would be the month and the value would be the total hours worked for that month. In the date-time API , that was added in Java 1.8, there is a Month enum so I would use that as the Map key.

Rather than using a JTextField to enter the hours worked, I would use a JSpinner .

In order to update the total hours worked, I would add a ChangeListener to the JSpinner model so that each time its value was changed, the text of the JLabel displaying total hours worked would get updated so as to display the new total.

The only thing remaining is to add an ActionListener to the JComboBox such that it displays the entered value for total hours worked whenever the user chooses a particular month.

Here is a minimal, reproducible example .

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.Month;
import java.util.HashMap;
import java.util.Map;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.SpinnerNumberModel;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class EnumCombo implements ActionListener, ChangeListener, Runnable {
    private Map<Month, Double>  hoursWorked;
    private JComboBox<Month>  monthsCombo;
    private JFrame  frame;
    private JLabel  totalHoursLabel;
    private JSpinner  hoursSpinner;

    public EnumCombo() {
        hoursWorked = new HashMap<Month, Double>(12);
        for (Month month : Month.values()) {
            hoursWorked.put(month, Double.valueOf(0));
        }
    }

    @Override // java.awt.event.ActionListener
    public void actionPerformed(ActionEvent event) {
        Object source = event.getSource();
        if (source instanceof JComboBox<?>) {
            JComboBox<?> combo = (JComboBox<?>) source;
            Object obj = combo.getSelectedItem();
            if (obj instanceof Month) {
                Month month = (Month) obj;
                hoursSpinner.setValue(hoursWorked.get(month));
            }
        }
    }

    @Override // javax.swing.event.ChangeListener
    public void stateChanged(ChangeEvent evt) {
        Object source = evt.getSource();
        if (source instanceof SpinnerNumberModel) {
            SpinnerNumberModel snm = (SpinnerNumberModel) source;
            Object obj = snm.getValue();
            if (obj instanceof Double) {
                Double value = (Double) obj;
                hoursWorked.put((Month) monthsCombo.getSelectedItem(), value);
                Double total = hoursWorked.values()
                                          .stream()
                                          .reduce(Double.valueOf(0),
                                                  (tot, val) -> tot + val);
                totalHoursLabel.setText(total.toString());
            }
        }
    }

    @Override
    public void run() {
        showGui();
    }

    private JPanel createInputPanel() {
        JPanel inputPanel = new JPanel();
        JLabel monthLabel = new JLabel("Month");
        inputPanel.add(monthLabel);
        monthsCombo = new JComboBox<Month>(Month.values());
        monthsCombo.addActionListener(this);
        inputPanel.add(monthsCombo);
        JLabel hoursLabel = new JLabel("Hours Worked");
        inputPanel.add(hoursLabel);
        SpinnerNumberModel snm = new SpinnerNumberModel(Double.valueOf(0),
                                                        Double.valueOf(0),
                                                        Double.valueOf(999),
                                                        Double.valueOf(1));
        snm.addChangeListener(this);
        hoursSpinner = new JSpinner(snm);
        inputPanel.add(hoursSpinner);
        return inputPanel;
    }

    private JPanel createTotalPanel() {
        JPanel totalPanel = new JPanel();
        JLabel label = new JLabel("Total Hours");
        totalPanel.add(label);
        totalHoursLabel = new JLabel("0");
        totalPanel.add(totalHoursLabel);
        return totalPanel;
    }

    private void showGui() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(createInputPanel(), BorderLayout.PAGE_START);
        frame.add(createTotalPanel(), BorderLayout.PAGE_END);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new EnumCombo());
    }
}

Note that method stateChanged , in the above code, uses the stream API which was also added in Java 1.8

Here is a screen capture of the running app.