I followed this tip on implementing a custom combo box renderer that allows me to pass in Objects and display specific data fields while also enabling the use of JComboBox key search features.
The code that was used in the article is given below:
package editor;
import java.awt.Component;
import javax.swing.ComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JList;
import javax.swing.UIManager;
import javax.swing.plaf.basic.BasicComboBoxRenderer;
//PROBLEM HERE<-------------------------------------------------------------------------
@SuppressWarnings("unchecked")
public abstract class KeySelectionRenderer extends BasicComboBoxRenderer implements JComboBox.KeySelectionManager {
private static final long serialVersionUID = 2334229124492928364L;
private long currentTime;
private long lastTime;
private final long timeFactor;
private String prefix = "";
/**
* This class can be used as the renderer and KeySelectionManager for an Object added to the ComboBoxModel.
*
* <p>
* 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.
*
* @param box
* A JComboBox object that is to use this KeySelectionRenderer.
*/
public KeySelectionRenderer(JComboBox box) {
box.setRenderer(this);
box.setKeySelectionManager(this);
Long value = (Long) UIManager.get("ComboBox.timeFactor");
timeFactor = (value == null ? 250L : value.longValue());
}
public KeySelectionRenderer(JList list) {
list.setCellRenderer(this);
Long value = (Long) UIManager.get("ComboBox.timeFactor");
timeFactor = (value == null ? 250L : value.longValue());
}
/**
* Implements 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) {
this.setText(getDisplayValue(item));
}
return this;
}
/**
* Implements the KeySelectionManager.
* */
@Override
public int selectionForKey(char aKey, ComboBoxModel model) {
this.currentTime = 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 (currentTime - 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 = currentTime;
// 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;
}
/**
* Finds 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;
}
/**
* 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);
}
Near the top of the code, I marked the problem out for you. You can see that I suppressed a warning, which is marking the issue where [icode]KeySelectionListener[/icode] is in general form, instead of having a Generic type. The problem is, I don’t know what to put the Generic type at. The suggested solutions by Eclipse is confusing me even more, so I kept the code like this when I releasing my update to my project.
Since the article didn’t explain how to put the Generic type in, I was wondering if anyone here can help me how to “remove” this warning. I just don’t like having my codes littered with yellow warnings, especially in this abstract class given above.
Thanks in advance.