Question

I am using a JTable in my application and wish to have 2 rows for headings, similar to this:

Is this even possible or will I have to do something else? If so, what? Using Supertitle-titleA, SuperTitle-titleB will take up too much space and make information redundant.

Answer 1

We had the same requirement in our last project. What I have found is an Implementation for a GroupableTableHeader on java2s.com. However, I have pimped it a bit, although I cannot recall what exactly. Beneath is the implementation of the three classes as how we use them.

ColumnGroup.java

import java.awt.Component;
import java.awt.Dimension;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.swing.JTable;
import javax.swing.table.TableCellRenderer;
import javax.swing.table.TableColumn;

/**
 * ColumnGroup
 * 
 * @version 1.0 20.10.1998
 * @author Nobuo Tamemasa
 */
public class ColumnGroup {

    protected TableCellRenderer renderer;

    protected List<TableColumn> columns;
    protected List<ColumnGroup> groups;

    protected String text;
    protected int margin = 0;

    public ColumnGroup(String text) {
        this(text, null);
    }

    public ColumnGroup(String text, TableCellRenderer renderer) {
        this.text = text;
        this.renderer = renderer;
        this.columns = new ArrayList<TableColumn>();
        this.groups = new ArrayList<ColumnGroup>();
    }

    public void add(TableColumn column) {
        columns.add(column);
    }

    public void add(ColumnGroup group) {
        groups.add(group);
    }

    /**
     * @param column
     *            TableColumn
     */
    public List<ColumnGroup> getColumnGroups(TableColumn column) {
        if (!contains(column)) {
            return Collections.emptyList();
        }
        List<ColumnGroup> result = new ArrayList<ColumnGroup>();
        result.add(this);
        if (columns.contains(column)) {
            return result;
        }
        for (ColumnGroup columnGroup : groups) {
            result.addAll(columnGroup.getColumnGroups(column));
        }
        return result;
    }

    private boolean contains(TableColumn column) {
        if (columns.contains(column)) {
            return true;
        }
        for (ColumnGroup group : groups) {
            if (group.contains(column)) {
                return true;
            }
        }
        return false;
    }

    public TableCellRenderer getHeaderRenderer() {
        return renderer;
    }

    public void setHeaderRenderer(TableCellRenderer renderer) {
        this.renderer = renderer;
    }

    public String getHeaderValue() {
        return text;
    }

    public Dimension getSize(JTable table) {
        TableCellRenderer renderer = this.renderer;
        if (renderer == null) {
            renderer = table.getTableHeader().getDefaultRenderer();
        }
        Component comp = renderer.getTableCellRendererComponent(table, getHeaderValue() == null || getHeaderValue().trim().isEmpty() ? " "
                : getHeaderValue(), false, false, -1, -1);
        int height = comp.getPreferredSize().height;
        int width = 0;
        for (ColumnGroup columnGroup : groups) {
            width += columnGroup.getSize(table).width;
        }
        for (TableColumn tableColumn : columns) {
            width += tableColumn.getWidth();
            width += margin;
        }
        return new Dimension(width, height);
    }

    public void setColumnMargin(int margin) {
        this.margin = margin;
        for (ColumnGroup columnGroup : groups) {
            columnGroup.setColumnMargin(margin);
        }
    }

}

GroupableTableHeader.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.swing.table.JTableHeader;
import javax.swing.table.TableColumn;
import javax.swing.table.TableColumnModel;

/**
 * GroupableTableHeader
 * 
 * @version 1.0 20.10.1998
 * @author Nobuo Tamemasa
 */
@SuppressWarnings("serial")
public class GroupableTableHeader extends JTableHeader {

    @SuppressWarnings("unused")
    private static final String uiClassID = "GroupableTableHeaderUI";

    protected List<ColumnGroup> columnGroups = new ArrayList<ColumnGroup>();

    public GroupableTableHeader(TableColumnModel model) {
        super(model);
        setUI(new GroupableTableHeaderUI());
        setReorderingAllowed(false);
        // setDefaultRenderer(new MultiLineHeaderRenderer());
    }

    @Override
    public void updateUI() {
        setUI(new GroupableTableHeaderUI());
    }

    @Override
    public void setReorderingAllowed(boolean b) {
        super.setReorderingAllowed(false);
    }

    public void addColumnGroup(ColumnGroup g) {
        columnGroups.add(g);
    }

    public List<ColumnGroup> getColumnGroups(TableColumn col) {
        for (ColumnGroup group : columnGroups) {
            List<ColumnGroup> groups = group.getColumnGroups(col);
            if (!groups.isEmpty()) {
                return groups;
            }
        }
        return Collections.emptyList();
    }

    public void setColumnMargin() {
        int columnMargin = getColumnModel().getColumnMargin();
        for (ColumnGroup group : columnGroups) {
            group.setColumnMargin(columnMargin);
        }
    }

}

GroupableTableHeaderUI.java

import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.swing.JComponent;
import javax.swing.UIManager;
import javax.swing.plaf.basic.BasicTableHeaderUI;
import javax.swing.table.TableCellRenderer;
import javax.swing.table.TableColumn;
import javax.swing.table.TableColumnModel;

public class GroupableTableHeaderUI extends BasicTableHeaderUI {

    protected GroupableTableHeader getHeader() {
        return (GroupableTableHeader) header;
    }

    @Override
    public void paint(Graphics g, JComponent c) {
        Rectangle clipBounds = g.getClipBounds();
        if (header.getColumnModel().getColumnCount() == 0) {
            return;
        }
        int column = 0;
        Dimension size = header.getSize();
        Rectangle cellRect = new Rectangle(0, 0, size.width, size.height);
        Map<ColumnGroup, Rectangle> groupSizeMap = new HashMap<ColumnGroup, Rectangle>();

        for (Enumeration<TableColumn> enumeration = header.getColumnModel().getColumns(); enumeration.hasMoreElements();) {
            cellRect.height = size.height;
            cellRect.y = 0;
            TableColumn aColumn = enumeration.nextElement();
            List<ColumnGroup> groups = getHeader().getColumnGroups(aColumn);
            int groupHeight = 0;
            for (ColumnGroup group : groups) {
                Rectangle groupRect = groupSizeMap.get(group);
                if (groupRect == null) {
                    groupRect = new Rectangle(cellRect);
                    Dimension d = group.getSize(header.getTable());
                    groupRect.width = d.width;
                    groupRect.height = d.height;
                    groupSizeMap.put(group, groupRect);
                }
                paintCell(g, groupRect, group);
                groupHeight += groupRect.height;
                cellRect.height = size.height - groupHeight;
                cellRect.y = groupHeight;
            }
            cellRect.width = aColumn.getWidth();
            if (cellRect.intersects(clipBounds)) {
                paintCell(g, cellRect, column);
            }
            cellRect.x += cellRect.width;
            column++;
        }
    }

    private void paintCell(Graphics g, Rectangle cellRect, int columnIndex) {
        TableColumn aColumn = header.getColumnModel().getColumn(columnIndex);
        TableCellRenderer renderer = aColumn.getHeaderRenderer();
        if (renderer == null) {
            renderer = getHeader().getDefaultRenderer();
        }
        Component c = renderer.getTableCellRendererComponent(header.getTable(), aColumn.getHeaderValue(), false, false,
                -1, columnIndex);

        c.setBackground(UIManager.getColor("control"));

        rendererPane.paintComponent(g, c, header, cellRect.x, cellRect.y, cellRect.width, cellRect.height, true);
    }

    private void paintCell(Graphics g, Rectangle cellRect, ColumnGroup cGroup) {
        TableCellRenderer renderer = cGroup.getHeaderRenderer();
        if (renderer == null) {
            renderer = getHeader().getDefaultRenderer();
        }

        Component component = renderer.getTableCellRendererComponent(header.getTable(), cGroup.getHeaderValue(), false,
                false, -1, -1);
        rendererPane
                .paintComponent(g, component, header, cellRect.x, cellRect.y, cellRect.width, cellRect.height, true);
    }

    private int getHeaderHeight() {
        int headerHeight = 0;
        TableColumnModel columnModel = header.getColumnModel();
        for (int column = 0; column < columnModel.getColumnCount(); column++) {
            TableColumn aColumn = columnModel.getColumn(column);
            TableCellRenderer renderer = aColumn.getHeaderRenderer();
            if (renderer == null) {
                renderer = getHeader().getDefaultRenderer();
            }

            Component comp = renderer.getTableCellRendererComponent(header.getTable(), aColumn.getHeaderValue(), false,
                    false, -1, column);
            int cHeight = comp.getPreferredSize().height;
            List<ColumnGroup> groups = getHeader().getColumnGroups(aColumn);
            for (ColumnGroup group : groups) {
                cHeight += group.getSize(header.getTable()).height;
            }
            headerHeight = Math.max(headerHeight, cHeight);
        }
        return headerHeight;
    }

    @Override
    public Dimension getPreferredSize(JComponent c) {
        int width = 0;
        for (Enumeration<TableColumn> enumeration = header.getColumnModel().getColumns(); enumeration.hasMoreElements();) {
            TableColumn aColumn = enumeration.nextElement();
            width += aColumn.getPreferredWidth();
        }
        return createHeaderSize(width);
    }

    private Dimension createHeaderSize(int width) {
        TableColumnModel columnModel = header.getColumnModel();
        width += columnModel.getColumnMargin() * columnModel.getColumnCount();
        if (width > Integer.MAX_VALUE) {
            width = Integer.MAX_VALUE;
        }
        return new Dimension(width, getHeaderHeight());
    }

}