How do i delete the JLabel from previous creation?

Question

I'm creating a calendar, and i use forloop to loop the days and add JLabel according to each day. However, whenever I change the month of the calendar, let say January has 31 days , and If I change the month to February for example, February will have 31 + 28 days, I'm really confused of how to solve this problem

Here's the code: MonthPanel.java

public class MonthPanel extends JPanel {

    private String[] headers = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
    private int realDay, realMonth, realYear, currentMonth, currentYear;
    private Toolbar toolbar;
    private String inputTotal = "";


    public MonthPanel() throws IOException {

        setLayout(new GridLayout(6,7));

        for (String header : headers) {
             add(new JLabel(header));
        }

        changeCalendar();
    }

    public void changeCalendar(int month) throws IOException {

    String[] months = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    int noDays, monthStart;

    Border border = BorderFactory.createLineBorder(Color.BLACK, 1);

    GregorianCalendar cal = new GregorianCalendar(2015, month, 1);
    noDays = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH);
    monthStart = cal.get(GregorianCalendar.DAY_OF_WEEK);

    for(int i=1; i<= noDays; i++) {

         JLabel label = new JLabel(String.valueOf(i));
          label.setBackground(Color.WHITE);
          label.setBorder(border);
          label.setOpaque(true);

          add(label); 

    }


    System.out.println(months[month]);
    System.out.println(noDays);

}

Toolbar.java

public class Toolbar extends JPanel {

    public JComboBox<Object> months;
    public JLabel monthName;
    private JLabel pictureName;
    private MonthListener monthListener;

    public Toolbar() throws IOException {

        ImageIcon img = new ImageIcon("/Users/naufal/Desktop/pictureC2.jpg");
        pictureName = new JLabel(img);

        String[] monthsList = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
        months = new JComboBox<Object>(monthsList);
        monthName = new JLabel(monthsList[0]);
        setLayout(new FlowLayout());

        add(months);
        add(monthName);
        add(pictureName);



    }

MainFrame.java - this is where the changes happen, if the user change the calendar it will changes

public class MainFrame extends JFrame {

    private Toolbar toolBar;
    private MonthPanel monthPanel;
    String[] monthsList = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};

    public MainFrame() throws IOException {
        super("Calendar App");
        setLayout(new BorderLayout());

        toolBar = new Toolbar();
        monthPanel = new MonthPanel();

        JComboBox getMonthBox = toolBar.getMonths();

        ActionListener acListener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                 int monthIndex = getMonthBox.getSelectedIndex();
                 try {

                    monthPanel.changeCalendar(monthIndex);
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
                 toolBar.monthName.setText(monthsList[boxCount]);


            }
        };

        toolBar.months.addActionListener(acListener);

        setSize(1200,900);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        add(toolBar, BorderLayout.NORTH);
        add(monthPanel);


    }

}

Intial Calendar

After I changed the month to february, it appends the current JLabel which is 31(January) JLabel with another 28(February) JLabel

Answer 1

I think this could will do the job you want.
If you have any question or don't understand feel free to ask.
How it works is described in the code by comments.

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Main extends JFrame implements ActionListener {

    private JComboBox<String> months;
    private String[] monthsList = { "January", "February", "March", "April",
            "May", "June", "July", "August", "September", "October",
            "November", "December" };
    private JPanel panel;

    private int[] days = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };// days
                                                                            // of
                                                                            // each
                                                                            // month

    public Main() {
        super("My Caleander!");

        months = new JComboBox<>(monthsList); // Adding months to Combo box.

        panel = new JPanel(); // Panel for adding labels inside.
        setLayout(new BorderLayout());

        panel.setLayout(new GridLayout(0, 7));// 0 for dynamic number of rows
                                                // and 7 for each week.

        for (int i = 0; i < 31; i++) {
            panel.add(new JLabel(String.valueOf(i + 1))); // Adding days of
                                                            // month January.
        }

        months.addActionListener(this);// Adding Action listener for responding
                                        // to change of month.

        add(months, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);

        setVisible(true);
        setLocationRelativeTo(null);// Putting JFrame to the center of screen.
        setSize(300, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

    }

    public static void main(String[] args) {

        new Main();

    }

    @Override
    public void actionPerformed(ActionEvent e) {// Listening to changes made by
                                                // ComboBox.

        panel.removeAll();
        int daysOfMonth = months.getSelectedIndex();// Getting the index of
                                                    // current month

        for (int i = 0; i < days[daysOfMonth]; i++) {// Adding the requiered
                                                        // number of months.
            panel.add(new JLabel(String.valueOf(i + 1)));
        }

        panel.revalidate();//Updating panel.
        revalidate();//Upadating frame.

    }

}

Answer 2

What is the parent container for label?

You may try repaint the label on parent container. Check the steps below to get parent and repaint it. Use this when event happens. I will leave the logic to you.

Container parent = label.getParent();
parent.remove(label);
parent.validate();
parent.repaint();

Answer 3

As an alternative, you can instantiate an size 31 array of JLabels, and use JPanel.remove() to remove all JLabels from day#noDays to day#31, and add them again if necessary.

You'd even save processing because you don't have to create new JLabels all the time because you're recycling them.

MonthPanel would look like this:

public class MonthPanel extends JPanel {

    private String[] headers = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
    private int realDay, realMonth, realYear, currentMonth, currentYear;
    private Toolbar toolbar;
    private String inputTotal = "";
    private JLabel[] labelArray;


    public MonthPanel() throws IOException {

        setLayout(new GridLayout(6,7));

        for (String header : headers) {
             add(new JLabel(header));
        }

        Border border = BorderFactory.createLineBorder(Color.BLACK, 1);

        /* Instantiate JLabel array */
        labelArray = new JLabel[31];
        for( int i = 0; i < 30; i++ ) {
            JLabel label = new JLabel(""+(i+1));
            label.setBackground(Color.WHITE);
            label.setBorder(border);
            label.setOpaque(true);
            labelArray[i] = label;
        }

        changeCalendar();
    }

    public void changeCalendar(int month) throws IOException {

    String[] months = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    int noDays, monthStart;

    GregorianCalendar lastMonth = new GregorianCalendar(2015, month-1, 1);
    noDaysLastMonth = lastMonth.getActualMaximum(GregorianCalendar.DAY_OF_MONTH);

    GregorianCalendar cal = new GregorianCalendar(2015, month, 1);
    noDays = cal.getActualMaximum(GregorianCalendar.DAY_OF_MONTH);
    monthStart = cal.get(GregorianCalendar.DAY_OF_WEEK);

    if( noDaysLastMonth < noDays ) { // add days if this month has more days than last month
        for( int i = noDaysLastMonth; i < noDays; i++ ) {
            add( labelArray[i] );
        }
    }
    else if ( noDays < noDaysLastMonth ) { // remove days if this month has less days than last month
        for( int i = noDays; i < noDaysLastMonth; i++ ) {
            remove( labelArray[i] );
        }
    }
    validate();
    repaint();

    System.out.println(months[month]);
    System.out.println(noDays);

}

Code unchecked though, but that's the logic.