JToolBar show arrow if too many buttons were added

Is there a way to have an arrow (like ) in JToolBar(API) when the visible container is smaller than the space all the buttons need?

(For illustration purposes see WebUI zkoss)

The UI manager (L&F) should be the normal one of swing.

Is there a way to have an arrow

It is not part of the API, so you will need to create your own.

You might be able to use the following to give you some ideas. This examples adds buttons to the left/right when there is not enough space for all the buttons so you can scroll to see each button:

import java.awt.*;
import java.util.List;
import java.util.ArrayList;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;


public class ScrollContainer extends JPanel
    implements ActionListener, ComponentListener
{
    private Container container;
    private List<Component> removedComponents = new ArrayList<Component>();
    private JButton forwardButton;
    private JButton backwardButton;

    public ScrollContainer(Container container)
    {
        this.container = container;
        setLayout( new BorderLayout(5, 0) );
        addComponentListener( this );

        //  Create buttons to control scrolling

        backwardButton = new BasicArrowButton( BasicArrowButton.WEST );
        configureButton( backwardButton );
        forwardButton = new BasicArrowButton( BasicArrowButton.EAST);
        configureButton( forwardButton );

        //  Layout the panel

        add( backwardButton, BorderLayout.WEST );
        add( container );
        add( forwardButton, BorderLayout.EAST );
    }

    //  Implement the ComponentListener

    public void componentResized(ComponentEvent e)
    {
        //  When all components cannot be shown, add the forward button

        int freeSpace = getSize().width - container.getPreferredSize().width;

        if (backwardButton.isVisible())
            freeSpace -= backwardButton.getPreferredSize().width;

        forwardButton.setVisible( freeSpace < 0 );

        //  We have free space, redisplay removed components

        while (freeSpace > 0 && ! removedComponents.isEmpty())
        {
            if (removedComponents.size() == 1)
                freeSpace += backwardButton.getPreferredSize().width;

            Object o = removedComponents.get(removedComponents.size() - 1);
            Component c = (Component)o;
            freeSpace -= c.getSize().width;

            if (freeSpace >= 0)
            {
                container.add(c, 0);
                removedComponents.remove(removedComponents.size() - 1);
            }
        }

        //  Some components still not shown, add the backward button

        backwardButton.setVisible( !removedComponents.isEmpty() );

//      repaint();

    }

    public void componentMoved(ComponentEvent e) {}
    public void componentShown(ComponentEvent e) {}
    public void componentHidden(ComponentEvent e) {}

    //  Implement the ActionListener

    public void actionPerformed(ActionEvent e)
    {
        Object source = e.getSource();

        //  Scroll the components in the container

        if (source == forwardButton)
            scrollForward();
        else
            scrollBackward();
    }

    /*
     *  Simulate scrolling forward
     *  by remove the first component from the container
     */
    private void scrollForward()
    {
        if (container.getComponentCount() == 1)
            return;

        //  Remove and save the first component

        Component c = container.getComponent(0);
        container.remove( c );
        removedComponents.add( c );

        //  Allow for backwards scrolling

        backwardButton.setVisible( true );

        //  All components are showing, hide the forward button

        int backwardButtonWidth = backwardButton.getPreferredSize().width;
        int containerWidth = container.getPreferredSize().width;
        int panelWidth = getSize().width;

        if (backwardButtonWidth + containerWidth <= panelWidth)
            forwardButton.setVisible( false );

        //  Force a repaint of the panel

        revalidate();
        repaint();
    }

    /*
     *  Simulate scrolling backward
     *  by adding a removed component back to the container
     */
    private void scrollBackward()
    {
        if (removedComponents.isEmpty())
            return;

        //  Add a removed component back to the container

        Object o = removedComponents.remove(removedComponents.size() - 1);
        Component c = (Component)o;
        container.add(c, 0);

        //  Display scroll buttons when necessary

        if (removedComponents.isEmpty())
            backwardButton.setVisible( false );

        forwardButton.setVisible( true );
        revalidate();
        repaint();
    }

    private void configureButton(JButton button)
    {
        button.setVisible( false );
        button.addActionListener( this );
    }

    private static void createAndShowGUI()
    {
        JToolBar toolBar = new JToolBar();
        toolBar.setFloatable(false);
        toolBar.add( new JButton("one") );
        toolBar.add( new JButton("two222222") );
        toolBar.add( new JButton("three") );
        toolBar.add( new JButton("four") );
        toolBar.add( new JButton("five") );
        toolBar.add( new JButton("six666666666") );
        toolBar.add( new JButton("seven") );
        toolBar.add( new JButton("eight") );
        toolBar.add( new JButton("nine9999999") );
        toolBar.add( new JButton("ten") );
        ScrollContainer container = new ScrollContainer(toolBar);

        JFrame frame = new JFrame("Scroll Container");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(container, BorderLayout.NORTH);
        frame.setLocationByPlatform( true );
        frame.pack();
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
    }
}

So you would need to modify the code to create a popup menu as required to contain the extra buttons.