Color individual JTable Cell based on content of cell?

Question

Okay, I know this question has been asked a ton on stack overflow. I've read almost every article. I can absolutely not get this too work. I made a table that serves as an availability calendar for a hotel, and I would like to color cell's with 0 rooms available red, and ones with more than 0 green. I've tried implementing a table cell renderer at no avail. Here is all of my code. What am I doing wrong?

package gui;

import entity.Inventory;
import entity.Room;
import java.awt.Color;
import java.awt.Component;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.LinkedList;
import javax.swing.BorderFactory;

import javax.swing.JComboBox;
import javax.swing.JPanel;
import javax.swing.JTable;
import javax.swing.table.DefaultTableCellRenderer;
import javax.swing.table.DefaultTableModel;
import tools.DateCalc;

public class Calendar extends JPanel {

    String[] years = {"2013", "2014"};
    JComboBox yearBox = new JComboBox(years);
    String[] months = {"January", "February", "March", "April", "May", "June", "July", "August",
        "September", "October", "November", "December"};
    JComboBox monthBox = new JComboBox(months);
    LinkedList<String> lTypes = Room.getRoomTypes();
    String[] types = lTypes.toArray(new String[0]);
    JComboBox typeBox = new JComboBox(types);

    CalendarModel model = new CalendarModel();
    JTable table = new JTable(model);

    public Calendar() {
        super();



        yearBox.setBounds(10, 10, 100, 30);
        yearBox.setSelectedIndex(0);
        yearBox.addItemListener(new ComboHandler());

        int selected = DateCalc.getNumMonth(DateCalc.getCurrentDate());

        monthBox.setSelectedIndex(selected);
        monthBox.addItemListener(new ComboHandler());
        // table.setBounds(10, 150, 550, 200);
        model.setMonth(Integer.parseInt((String)yearBox.getSelectedItem()), monthBox.getSelectedIndex(), 0);
        typeBox.addItemListener(new ComboHandler());
        add(monthBox);
        add(yearBox);
        add(typeBox);
        table.setGridColor(Color.black);
        table.setShowGrid(true);
        table.setRowHeight(40);
        table.setBorder(BorderFactory.createLineBorder(Color.black));

        table.setDefaultRenderer(String.class, new MyCellRender());
        add(table);



        setSize(600, 800);
        setVisible(true);
    }

    public static void main(String[] args) {
        Calendar app = new Calendar();
    }

    public class ComboHandler implements ItemListener {

        public void itemStateChanged(ItemEvent e) {

            model.setMonth(Integer.parseInt((String)yearBox.getSelectedItem()), monthBox.getSelectedIndex(), typeBox.getSelectedIndex());
            table.repaint();

        }
    }

    public class MyCellRender extends DefaultTableCellRenderer {

        @Override
        public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) {
            Component c = super.getTableCellRendererComponent(table, value,
                                          isSelected, hasFocus,
                                          row, column);
            for (int i =0; i < 7; i++){
                for (int j = 0; j < j; j++){
                    String positive = (String)table.getModel().getValueAt(i,j);
                    System.out.println(positive);
                    int val = positive.indexOf(" 0 ");
                    if (val < 0)
                       c.setBackground(Color.green);
                    else{
                        c.setBackground(Color.red);
                    }
                }
            }

            return c;
        }
    }

    class CalendarModel extends DefaultTableModel {

        String[] days = {"  Sun", "  Mon", "  Tue", "  Wed", "  Thu", "  Fri", "  Sat"};
        int[] numDays = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
        String[][] calendar = new String[7][7];

        public CalendarModel() {
            for (int i = 0; i < days.length; ++i) {
                calendar[0][i] = days[i];
            }
            for (int i = 1; i < 7; ++i) {
                for (int j = 0; j < 7; ++j) {
                    calendar[i][j] = " ";
                }
            }
        }

        @Override
        public boolean isCellEditable(int row, int column){
            return false;
        }
        public int getRowCount() {
            return 7;
        }

        public int getColumnCount() {
            return 7;
        }

        public String getValueAt(int row, int column) {
            return calendar[row][column];
        }

        public void setValueAt(String value, int row, int column) {
            calendar[row][column] = value;
        }

        public void setMonth(int year, int month, int flag) {
            for (int i = 1; i < 7; ++i) {
                for (int j = 0; j < 7; ++j) {
                    calendar[i][j] = " ";
                }
            }
            java.util.Calendar cal = java.util.Calendar.getInstance();
            cal.set(year, month, 1);
            Date date = cal.getTime();

            DateFormat df = new SimpleDateFormat("MMddyyyy");

            String start = df.format(date);
            int offset = cal.get(java.util.Calendar.DAY_OF_WEEK)-1;

            offset += 7;
            int num = daysInMonth(year, month);
            for (int i = 0; i < num; ++i) {
                String target = DateCalc.addDay(start, i);
                Inventory inventory = Inventory.fromDBObject(target);
                String type = (String)typeBox.getSelectedItem();
                String beds = inventory.getField(type);
                calendar[offset / 7][offset % 7] = "  " + Integer.toString(i + 1)
                        + ".  " + beds;
                ++offset;

            }
        }

        public boolean isLeapYear(int year) {
            if (year % 4 == 0) {
                return true;
            }
            return false;
        }

        public int daysInMonth(int year, int month) {
            int days = numDays[month];
            if (month == 1 && isLeapYear(year)) {
                ++days;
            }
            return days;
        }
    }
}

Answer 1

If the String class is used as the column class

table.setDefaultRenderer(String.class, new MyCellRender());

then, the column class of the TableModel should match:

@Override
public Class<?> getColumnClass(int columnIndex) {
   return String.class;
}

---

Also, there's an issue in getTableCellRendererComponent , in that the inner loop will not be executed

for (int i = 0; i < 7; i++) {
   for (int j = 0; j < j; j++) {
                   ^^^^^---------condition always false, loop will not execute

It's unclear why these loops are required as getTableCellRendererComponent is invoked for every cell component regardless.