import javax.swing.*;
import javax.swing.text.*;
import java.awt.event.*;

public class S16MaximumMatch extends PlainDocument {
    JComboBox comboBox;
    ComboBoxModel model;
    JTextComponent editor;
    // flag to indicate if setSelectedItem has been called
    // subsequent calls to remove/insertString should be ignored
    boolean selecting=false;
    boolean hidePopupOnFocusLoss;
    boolean hitBackspace=false;
    boolean hitBackspaceOnSelection;
    
    public S16MaximumMatch(final JComboBox comboBox) {
        this.comboBox = comboBox;
        model = comboBox.getModel();
        editor = (JTextComponent) comboBox.getEditor().getEditorComponent();
        editor.setDocument(this);
        comboBox.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (!selecting) highlightCompletedText(0);
            }
        });
        editor.addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent e) {
                if (comboBox.isDisplayable()) comboBox.setPopupVisible(true);
                hitBackspace=false;
                switch (e.getKeyCode()) {
                    // determine if the pressed key is backspace (needed by the remove method)
                    case KeyEvent.VK_BACK_SPACE : hitBackspace=true;
                                                  hitBackspaceOnSelection=editor.getSelectionStart()!=editor.getSelectionEnd();
                                                  break;
                    // ignore delete key
                    case KeyEvent.VK_DELETE : e.consume();
                                              comboBox.getToolkit().beep();
                                              break;
                }
            }
        });
        // Bug 5100422 on Java 1.5: Editable JComboBox won't hide popup when tabbing out
        hidePopupOnFocusLoss=System.getProperty("java.version").startsWith("1.5");
        // Highlight whole text when gaining focus
        editor.addFocusListener(new FocusAdapter() {
            public void focusGained(FocusEvent e) {
                highlightCompletedText(0);
            }
            public void focusLost(FocusEvent e) {
                // Workaround for Bug 5100422 - Hide Popup on focus loss
                if (hidePopupOnFocusLoss) comboBox.setPopupVisible(false);
            }
        });
        // Handle initially selected object
        Object selected = comboBox.getSelectedItem();
        if (selected!=null) setText(selected.toString());
        highlightCompletedText(0);
    }
    
    public void remove(int offs, int len) throws BadLocationException {
        // return immediately when selecting an item
        if (selecting) return;
        if (hitBackspace) {
            // user hit backspace => move the selection backwards
            // old item keeps being selected
            if (offs>0) {
                if (hitBackspaceOnSelection) offs--;
            } else {
                // User hit backspace with the cursor positioned on the start => beep
                comboBox.getToolkit().beep(); // when available use: UIManager.getLookAndFeel().provideErrorFeedback(comboBox);
            }
            highlightCompletedText(offs);
        } else {
            super.remove(offs, len);
        }
    }
    
    public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
        // return immediately when selecting an item
        if (selecting) return;
        // insert the string into the document
        super.insertString(offs, str, a);
        // lookup and select a matching item
        boolean match=false;
        Object item = lookupItem(getText(0, getLength()));
        if (item != null) {
            match=true;
            setSelectedItem(item);
        } else {
            // keep old item selected if there is no match
            item = comboBox.getSelectedItem();
            // imitate no insert (later on offs will be incremented by str.length(): selection won't move forward)
            offs = offs-str.length();
            // provide feedback to the user that his input has been received but can not be accepted
            comboBox.getToolkit().beep(); // when available use: UIManager.getLookAndFeel().provideErrorFeedback(comboBox);
        }

        if (match) offs = getMaximumMatchingOffset(getText(0, getLength()), item);
        else offs+=str.length();

        setText(item.toString());
        // select the completed part
        highlightCompletedText(offs);
    }
    
    private void setText(String text) {
        try {
            // remove all text and insert the completed string
            super.remove(0, getLength());
            super.insertString(0, text, null);
        } catch (BadLocationException e) {
            throw new RuntimeException(e.toString());
        }
    }
    
    private void highlightCompletedText(int start) {
        editor.setCaretPosition(getLength());
        editor.moveCaretPosition(start);
    }
    
    private void setSelectedItem(Object item) {
        selecting = true;
        model.setSelectedItem(item);
        selecting = false;
    }
    
    private Object lookupItem(String pattern) {
        Object selectedItem = model.getSelectedItem();
        // only search for a different item if the currently selected does not match
        if (selectedItem != null && startsWithIgnoreCase(selectedItem.toString(), pattern)) {
            return selectedItem;
        } else {
            // iterate over all items
            for (int i=0, n=model.getSize(); i < n; i++) {
                Object currentItem = model.getElementAt(i);
                // current item starts with the pattern?
                if (startsWithIgnoreCase(currentItem.toString(), pattern)) {
                    return currentItem;
                }
            }
        }
        // no item starts with the pattern => return null
        return null;
    }
    
    // checks if str1 starts with str2 - ignores case
    private boolean startsWithIgnoreCase(String str1, String str2) {
        return str1.toUpperCase().startsWith(str2.toUpperCase());
    }
    
    // calculates how many characters are predetermined by the given pattern.
    private int getMaximumMatchingOffset(String pattern, Object selectedItem) {
        String selectedAsString=selectedItem.toString();
        int match=selectedAsString.length();
        // look for items that match the given pattern
        for (int i=0, n=model.getSize(); i < n; i++) {
            String itemAsString = model.getElementAt(i).toString();
            if (startsWithIgnoreCase(itemAsString, pattern)) {
                // current item matches the pattern
                // how many leading characters have the selected and the current item in common?
                int tmpMatch=equalStartLength(itemAsString, selectedAsString);
                if (tmpMatch < match) match=tmpMatch;
            }
        }
        return match;
    }
    
    // returns how many leading characters two strings have in common?
    private static int equalStartLength(String str1, String str2) {
        char[] ch1 = str1.toUpperCase().toCharArray();
        char[] ch2 = str2.toUpperCase().toCharArray();
        int n = ch1.length>ch2.length?ch2.length:ch1.length;
        for (int i=0; i<n; i++) {
            if (ch1[i]!=ch2[i]) return i;
        }
        return n;
    }
    
    private static void createAndShowGUI() {
        // the combo box (add/modify items if you like to)
        JComboBox comboBox = new JComboBox(new Object[] {"Ester", "Jordi", "Jordina", "Jorge", "Sergi"});
        // has to be editable
        comboBox.setEditable(true);
        // change the editor's document
        new S16MaximumMatch(comboBox);
        
        // create and show a window containing the combo box
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(3);
        frame.getContentPane().add(comboBox);
        frame.pack(); frame.setVisible(true);
    }
    
    
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}