How can I change the shape of a JTabbedPane tab?

I am trying to change the shape of the tabs in a JTabbedPane. Using setTabComponentAt(0, someComponent); doesn't change the exterior of the tab, which is a rectangle with a diagonal top-left corner. What may be done to change the shape?

correct way is only to change Look and Feel, nice example from Old.Java.Forums.Sun

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.JTextArea;

public class TabbedPane extends JPanel {

    private static final long serialVersionUID = 1L;

    public TabbedPane() {
        setLayout(new BorderLayout());
        JPanel jp = new JPanel();
        jp.setLayout(new BorderLayout());
        JTabbedPane tb = new JTabbedPane();
        tb.setUI(new CustomTabbedPaneUI());
        tb.add("Tab1", new JTextArea(""));
        tb.add("Tab2", new JTextArea(""));
        tb.add("Tab3", new JTextArea(""));
        tb.add("Tab4", new JTextArea(""));
        tb.add("Tab5", new JTextArea(""));
        jp.add(tb, BorderLayout.CENTER);
        add(jp, BorderLayout.CENTER);
        tb.setEnabledAt(1, false);
        tb.setEnabledAt(3, false);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.getContentPane().add(new TabbedPane());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 200);
        frame.setVisible(true);
    }
}

and

import java.util.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.plaf.*;
import javax.swing.plaf.basic.*;
import javax.swing.text.View;

public class CustomTabbedPaneUI extends BasicTabbedPaneUI {

    private Color selectColor;
    private Color deSelectColor;
    private int inclTab = 4;
    private int anchoFocoV = inclTab;
    private int anchoFocoH = 4;
    private int anchoCarpetas = 18;
    private Polygon shape;

    public static ComponentUI createUI(JComponent c) {
        return new CustomTabbedPaneUI();
    }

    @Override
    protected void installDefaults() {
        super.installDefaults();
        selectColor = new Color(250, 192, 192);
        deSelectColor = new Color(197, 193, 168);
        tabAreaInsets.right = anchoCarpetas;
    }

    @Override
    protected void paintTabArea(Graphics g, int tabPlacement, int selectedIndex) {
        if (runCount > 1) {
            int lines[] = new int[runCount];
            for (int i = 0; i < runCount; i++) {
                lines[i] = rects[tabRuns[i]].y + (tabPlacement == TOP ? maxTabHeight : 0);
            }
            Arrays.sort(lines);
            if (tabPlacement == TOP) {
                int fila = runCount;
                for (int i = 0; i < lines.length - 1; i++, fila--) {
                    Polygon carp = new Polygon();
                    carp.addPoint(0, lines[i]);
                    carp.addPoint(tabPane.getWidth() - 2 * fila - 2, lines[i]);
                    carp.addPoint(tabPane.getWidth() - 2 * fila, lines[i] + 3);
                    if (i < lines.length - 2) {
                        carp.addPoint(tabPane.getWidth() - 2 * fila, lines[i + 1]);
                        carp.addPoint(0, lines[i + 1]);
                    } else {
                        carp.addPoint(tabPane.getWidth() - 2 * fila, lines[i] + rects[selectedIndex].height);
                        carp.addPoint(0, lines[i] + rects[selectedIndex].height);
                    }
                    carp.addPoint(0, lines[i]);
                    g.setColor(hazAlfa(fila));
                    g.fillPolygon(carp);
                    g.setColor(darkShadow.darker());
                    g.drawPolygon(carp);
                }
            } else {
                int fila = 0;
                for (int i = 0; i < lines.length - 1; i++, fila++) {
                    Polygon carp = new Polygon();
                    carp.addPoint(0, lines[i]);
                    carp.addPoint(tabPane.getWidth() - 2 * fila - 1, lines[i]);
                    carp.addPoint(tabPane.getWidth() - 2 * fila - 1, lines[i + 1] - 3);
                    carp.addPoint(tabPane.getWidth() - 2 * fila - 3, lines[i + 1]);
                    carp.addPoint(0, lines[i + 1]);
                    carp.addPoint(0, lines[i]);
                    g.setColor(hazAlfa(fila + 2));
                    g.fillPolygon(carp);
                    g.setColor(darkShadow.darker());
                    g.drawPolygon(carp);
                }
            }
        }
        super.paintTabArea(g, tabPlacement, selectedIndex);
    }

    @Override
    protected void paintTabBackground(Graphics g, int tabPlacement, int tabIndex, int x, int y, int w, int h, boolean isSelected) {
        Graphics2D g2D = (Graphics2D) g;
        GradientPaint gradientShadow;
        int xp[] = null; // Para la forma
        int yp[] = null;
        switch (tabPlacement) {
            case LEFT:
                xp = new int[]{x, x, x + w, x + w, x};
                yp = new int[]{y, y + h - 3, y + h - 3, y, y};
                gradientShadow = new GradientPaint(x, y, new Color(100, 100, 255), x, y + h, Color.ORANGE);
                break;
            case RIGHT:
                xp = new int[]{x, x, x + w - 2, x + w - 2, x};
                yp = new int[]{y, y + h - 3, y + h - 3, y, y};
                gradientShadow = new GradientPaint(x, y, new Color(100, 100, 255), x, y + h, new Color(153, 186, 243));
                break;
            case BOTTOM:
                xp = new int[]{x, x, x + 3, x + w - inclTab - 6, x + w - inclTab - 2, x + w - inclTab, x + w - 3, x};
                yp = new int[]{y, y + h - 3, y + h, y + h, y + h - 1, y + h - 3, y, y};
                gradientShadow = new GradientPaint(x, y, new Color(100, 100, 255), x, y + h, Color.BLUE);
                break;
            case TOP:
            default:
                xp = new int[]{x, x, x + 3, x + w - inclTab - 6, x + w - inclTab - 2, x + w - inclTab, x + w - inclTab, x};
                yp = new int[]{y + h, y + 3, y, y, y + 1, y + 3, y + h, y + h};
                gradientShadow = new GradientPaint(0, 0, Color.ORANGE, 0, y + h / 2, new Color(240, 255, 210));
                break;
        }
        // ;
        shape = new Polygon(xp, yp, xp.length);
        if (isSelected) {
            g2D.setColor(selectColor);
            g2D.setPaint(gradientShadow);
        } else {
            if (tabPane.isEnabled() && tabPane.isEnabledAt(tabIndex)) {
                g2D.setColor(deSelectColor);
                GradientPaint gradientShadowTmp = new GradientPaint(0, 0, new Color(255, 255, 200), 0, y + h / 2, new Color(240, 255, 210));
                g2D.setPaint(gradientShadowTmp);
            } else {
                GradientPaint gradientShadowTmp = new GradientPaint(0, 0, new Color(240, 255, 210), 0, y + 15 + h / 2, new Color(204, 204, 204));
                g2D.setPaint(gradientShadowTmp);
            }
        }
        //selectColor = new Color(255, 255, 200);
        //deSelectColor = new Color(240, 255, 210);
        g2D.fill(shape);
        if (runCount > 1) {
            g2D.setColor(hazAlfa(getRunForTab(tabPane.getTabCount(), tabIndex) - 1));
            g2D.fill(shape);
        }
        g2D.fill(shape);
    }

    @Override
    protected void paintText(Graphics g, int tabPlacement, Font font, FontMetrics metrics, int tabIndex, String title, Rectangle textRect, boolean isSelected) {
        super.paintText(g, tabPlacement, font, metrics, tabIndex, title, textRect, isSelected);
        g.setFont(font);
        View v = getTextViewForTab(tabIndex);
        if (v != null) {
            // html
            v.paint(g, textRect);
        } else {
            // plain text
            int mnemIndex = tabPane.getDisplayedMnemonicIndexAt(tabIndex);
            if (tabPane.isEnabled() && tabPane.isEnabledAt(tabIndex)) {
                g.setColor(tabPane.getForegroundAt(tabIndex));
                BasicGraphicsUtils.drawStringUnderlineCharAt(g, title, mnemIndex, textRect.x, textRect.y + metrics.getAscent());
            } else { // tab disabled
                g.setColor(Color.BLACK);
                BasicGraphicsUtils.drawStringUnderlineCharAt(g, title, mnemIndex, textRect.x, textRect.y + metrics.getAscent());
                g.setColor(tabPane.getBackgroundAt(tabIndex).darker());
                BasicGraphicsUtils.drawStringUnderlineCharAt(g, title, mnemIndex, textRect.x - 1, textRect.y + metrics.getAscent() - 1);
            }
        }
    }
    /*protected void paintText(Graphics g, int tabPlacement, Font font, FontMetrics metrics, int tabIndex, String title, Rectangle textRect, boolean isSelected) {
    g.setFont(font);
    View v = getTextViewForTab(tabIndex);
    if (v != null) {
    // html
    v.paint(g, textRect);
    } else {
    // plain text
    int mnemIndex = tabPane.getDisplayedMnemonicIndexAt(tabIndex);

    if (tabPane.isEnabled() && tabPane.isEnabledAt(tabIndex)) {
    Color fg = tabPane.getForegroundAt(tabIndex);
    if (isSelected && (fg instanceof UIResource)) {
    Color selectedFG = UIManager.getColor("TabbedPane.selectedForeground");
    if (selectedFG != null) {
    fg = selectedFG;
    }
    }
    g.setColor(fg);
    SwingUtilities2.drawStringUnderlineCharAt(tabPane, g, title, mnemIndex, textRect.x, textRect.y + metrics.getAscent());

    } else { // tab disabled
    //PAY ATTENTION TO HERE
    g.setColor(tabPane.getBackgroundAt(tabIndex).brighter());
    SwingUtilities2.drawStringUnderlineCharAt(tabPane, g, title, mnemIndex, textRect.x, textRect.y + metrics.getAscent());
    g.setColor(tabPane.getBackgroundAt(tabIndex).darker());
    SwingUtilities2.drawStringUnderlineCharAt(tabPane, g, title, mnemIndex,
    textRect.x - 1, textRect.y + metrics.getAscent() - 1);
    }
    }
    }*/

    @Override
    protected int calculateTabWidth(int tabPlacement, int tabIndex, FontMetrics metrics) {
        return 20 + inclTab + super.calculateTabWidth(tabPlacement, tabIndex, metrics);
    }

    @Override
    protected int calculateTabHeight(int tabPlacement, int tabIndex, int fontHeight) {
        if (tabPlacement == LEFT || tabPlacement == RIGHT) {
            return super.calculateTabHeight(tabPlacement, tabIndex, fontHeight);
        } else {
            return anchoFocoH + super.calculateTabHeight(tabPlacement, tabIndex, fontHeight);
        }
    }

    @Override
    protected void paintTabBorder(Graphics g, int tabPlacement, int tabIndex, int x, int y, int w, int h, boolean isSelected) {
    }

    @Override
    protected void paintFocusIndicator(Graphics g, int tabPlacement, Rectangle[] rects, int tabIndex, Rectangle iconRect, Rectangle textRect, boolean isSelected) {
        if (tabPane.hasFocus() && isSelected) {
            g.setColor(UIManager.getColor("ScrollBar.thumbShadow"));
            g.drawPolygon(shape);
        }
    }

    protected Color hazAlfa(int fila) {
        int alfa = 0;
        if (fila >= 0) {
            alfa = 50 + (fila > 7 ? 70 : 10 * fila);
        }
        return new Color(0, 0, 0, alfa);
    }
}

The shape is under the aegis of the tabbed pane's UI delegate, which descends from TabbedPaneUI. The MetalTabbedPaneUI subclass is an example that may help you decide how badly you want to replace the delegate.

You can put html tags into the first parameter of addTab method as following :

MyJTabbedPane.addTab("<html><h1 style='padding:20px;'>TEST</h1></html>", new JPanel());