I have extended JTable so it can sort the data alphabetically and separate the data by sections according to their first letter.
See this question and marked answer for more clarification
The extended table works fine. However when sorted, by clicking on the table's header, I am facing a problem when scrolling down the table (using mouse-wheel). 
Here is the code to the extended table. (Note: you can also find this code in the hyperlink above).
import java.awt.BorderLayout;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.util.Map;
import java.util.NavigableMap;
import java.util.TreeMap;
import javax.swing.JFrame;
import javax.swing.JTable;
import javax.swing.RowSorter;
import javax.swing.SortOrder;
import javax.swing.SwingConstants;
import javax.swing.SwingUtilities;
import javax.swing.event.RowSorterEvent;
import javax.swing.event.TableModelEvent;
import javax.swing.table.TableModel;
import javax.swing.JScrollPane;
import javax.swing.table.DefaultTableModel;
public class SectionedTable
extends JTable {
private static final long serialVersionUID = 1;
private final NavigableMap<Integer, String> sectionHeadings
= new TreeMap<>();
private final NavigableMap<Integer, Integer> rowTopEdges
= new TreeMap<>();
// Used when calling SwingUtilities.layoutCompoundLabel.
private final Rectangle iconBounds = new Rectangle();
private final Rectangle textBounds = new Rectangle();
public SectionedTable() {
init();
}
public SectionedTable(TableModel model) {
super(model);
init();
}
private void init() {
setShowGrid(false);
setAutoCreateRowSorter(true);
recomputeSections();
recomputeRowPositions();
}
private void recomputeSections() {
if (sectionHeadings == null) {
return;
}
sectionHeadings.clear();
RowSorter<? extends TableModel> sorter = getRowSorter();
if (sorter == null) {
return;
}
for (RowSorter.SortKey key : sorter.getSortKeys()) {
SortOrder order = key.getSortOrder();
if (order != SortOrder.UNSORTED) {
int sortColumn = key.getColumn();
String lastSectionStart = "";
int rowCount = getRowCount();
for (int row = 0; row < rowCount; row++) {
System.out.println("row er : " + row);
System.out.println("rowcount er : " + rowCount);
System.out.println("sortColumn er : " + sortColumn);
Object value = getValueAt(row, sortColumn);
if (value == null) {
value = "?";
}
String s = value.toString();
if (s.isEmpty()) {
s = "?";
}
String sectionStart = s.substring(0,
s.offsetByCodePoints(0, 1));
sectionStart = sectionStart.toUpperCase();
if (!sectionStart.equals(lastSectionStart)) {
sectionHeadings.put(row, sectionStart);
lastSectionStart = sectionStart;
}
}
break;
}
}
}
private void recomputeRowPositions() {
if (rowTopEdges == null) {
return;
}
rowTopEdges.clear();
int y = getInsets().top;
int rowCount = getRowCount();
int rowHeight = getRowHeight();
for (int row = 0; row < rowCount; row++) {
rowTopEdges.put(y, row);
y += getRowHeight(row);
if (sectionHeadings.containsKey(row)) {
y += rowHeight;
}
}
}
@Override
public void tableChanged(TableModelEvent event) {
//super.tableChanged(event);
recomputeSections();
recomputeRowPositions();
super.tableChanged(event);
}
@Override
public void sorterChanged(RowSorterEvent event) {
recomputeSections();
recomputeRowPositions();
super.sorterChanged(event);
}
@Override
public void validate() {
super.validate();
recomputeRowPositions();
}
@Override
public int rowAtPoint(Point location) {
Map.Entry<Integer, Integer> entry = rowTopEdges.floorEntry(location.y);
if (entry != null) {
int row = entry.getValue();
return row;
}
return -1;
}
@Override
public Rectangle getCellRect(int row,
int column,
boolean includeSpacing) {
Rectangle rect = super.getCellRect(row, column, includeSpacing);
int sectionHeadingsAbove = sectionHeadings.headMap(row, true).size();
rect.y += sectionHeadingsAbove * getRowHeight();
return rect;
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
boolean ltr = getComponentOrientation().isLeftToRight();
int rowHeight = getRowHeight();
FontMetrics metrics = g.getFontMetrics();
int ascent = metrics.getAscent();
for (Map.Entry<Integer, String> entry : sectionHeadings.entrySet()) {
int row = entry.getKey();
String heading = entry.getValue();
Rectangle bounds = getCellRect(row, 0, true);
bounds.y -= rowHeight;
bounds.width = getWidth();
bounds.grow(-6, 0);
iconBounds.setBounds(0, 0, 0, 0);
textBounds.setBounds(0, 0, 0, 0);
String text = SwingUtilities.layoutCompoundLabel(this,
metrics, heading, null,
SwingConstants.CENTER, SwingConstants.LEADING,
SwingConstants.CENTER, SwingConstants.CENTER,
bounds, iconBounds, textBounds, 0);
g.drawString(text, textBounds.x, textBounds.y + ascent);
int lineY = textBounds.y + ascent / 2;
if (ltr) {
g.drawLine(textBounds.x + textBounds.width + 12, lineY,
getWidth() - getInsets().right - 12, lineY);
} else {
g.drawLine(textBounds.x - 12, lineY,
getInsets().left + 12, lineY);
}
}
}
public static void main(String[] args) {
DefaultTableModel model;
Object[][] data = new Object[50][5];
String[] columnNames = {"First Name",
"Last Name",
"Sport",
"# of Years",
"Vegetarian"};
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 5; j++) {
data[i][j] = "Amy";
}
}
for (int i = 10; i < 20; i++) {
for (int j = 0; j < 5; j++) {
data[i][j] = "Bob";
}
}
for (int i = 20; i < 30; i++) {
for (int j = 0; j < 5; j++) {
data[i][j] = "Joe";
}
}
for (int i = 30; i < 50; i++) {
for (int j = 0; j < 5; j++) {
data[i][j] = "M";
}
}
SectionedTable table = new SectionedTable();
model = new DefaultTableModel(data, columnNames);
table.setModel(model);
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTable table = new SectionedTable();
table.setModel(model);
JScrollPane scrollPane = new JScrollPane(table);
frame.add(scrollPane, BorderLayout.CENTER);
frame.setSize(500, 500);
frame.setVisible(true);
}
});
}
}
I've been struggling to find out what might cause this problem and I'm not near any solution. I think it might be at the rowAtPoint() or getCellRect(), but I'm not sure. Can someone spot where this problem might lie in the code?
