KeySelectionRenderer.java

import java.awt.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;

/*
 *  This class can be used as the renderer and KeySelectionManager for an
 *	Object added to the ComboBoxModel.
 *
 *  The class must be extended and the getDisplayValue() method must be
 *  implemented. This method will return a String to be rendered in the
 *  JComboBox. The same String will be used to do key selection of an
 *  item in the ComboBoxModel.
 */
abstract class KeySelectionRenderer extends BasicComboBoxRenderer
	implements JComboBox.KeySelectionManager
{
	//  Used by the KeySelectionManager implementation to determine when to
	//  start a new search or append typed character to the existing search.

	private long timeFactor;
	private long lastTime;
	private long time;
	private String prefix = "";

	public KeySelectionRenderer(JComboBox comboBox)
	{
		comboBox.setRenderer( this );
		comboBox.setKeySelectionManager( this );

		Long l = (Long)UIManager.get("ComboBox.timeFactor");
		timeFactor = l == null ? 1000L : l.longValue();
	}

	/**
	 *  This method must be implemented in the extended class.
	 *
	 *  @param item an item from the ComboBoxModel
	 *  @returns a String containing the text to be rendered for this item.
	*/
	public abstract String getDisplayValue(Object item);

	//  Implement the renderer

	@Override
	public Component getListCellRendererComponent(
		JList list, Object item, int index, boolean isSelected, boolean hasFocus)
	{
		super.getListCellRendererComponent(list, item, index, isSelected, hasFocus);

		if (item != null)
		{
			setText( getDisplayValue(item) );
		}

		return this;
	}

	//  Implement the KeySelectionManager

	@Override
	public int selectionForKey(char aKey, ComboBoxModel model)
	{
		time = System.currentTimeMillis();

		//  Get the index of the currently selected item

		int size = model.getSize();
		int startIndex = -1;
		Object selectedItem = model.getSelectedItem();

		if (selectedItem != null)
		{
			for (int i = 0; i < size; i++)
			{
				if ( selectedItem == model.getElementAt(i) )
				{
					startIndex  =  i;
					break;
				}
			}
		}

		//  Determine the "prefix" to be used when searching the model. The
		//  prefix can be a single letter or multiple letters depending on how
		//  fast the user has been typing and on which letter has been typed.

		if (time - lastTime < timeFactor)
		{
			if((prefix.length() == 1) && (aKey == prefix.charAt(0)))
			{
				// Subsequent same key presses move the keyboard focus to the next
				// object that starts with the same letter.
				startIndex++;
			}
			else
			{
				prefix += aKey;
			}
		}
		else
		{
			startIndex++;
			prefix = "" + aKey;
		}

		lastTime = time;

		//  Search from the current selection and wrap when no match is found

		if (startIndex < 0 || startIndex >= size)
		{
			startIndex = 0;
		}

		int index = getNextMatch(prefix, startIndex, size, model);

		if (index < 0)
		{
			// wrap
			index = getNextMatch(prefix, 0, startIndex, model);
		}

		return index;
	}

	/*
	**  Find the index of the item in the model that starts with the prefix.
	*/
	private int getNextMatch(String prefix, int start, int end, ComboBoxModel model)
	{
		for (int i = start; i < end; i++ )
		{
			Object item = model.getElementAt(i);

			if (item != null)
			{
				String displayValue = getDisplayValue( item ).toLowerCase();

				if (displayValue.startsWith(prefix))
				{
					return i;
				}
			}
		}

		return -1;
	}
}