import javax.swing.*;
import javax.swing.text.*;

public class S02BrokenAutoSelection extends PlainDocument {
    ComboBoxModel model;
    
    public S02BrokenAutoSelection(ComboBoxModel model) {
        this.model = model;
    }
    
    public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
        System.out.println("insert " + str + " at " + offs);
        // insert the string into the document
        super.insertString(offs, str, a);
        // get the resulting string
        String content = getText(0, getLength());
        // lookup a matching item
        Object item = lookupItem(content);
        // select the item (or deselect if null)
        if(item!=model.getSelectedItem()) System.out.println("Selecting '" + item + "'");
        model.setSelectedItem(item);
    }
    
    private Object lookupItem(String pattern) {
        // 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 (currentItem.toString().startsWith(pattern)) {
                return currentItem;
            }
        }
        // no item starts with the pattern => return null
        return null;
    }
    
    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);
        // get the combo boxes editor component
        JTextComponent editor = (JTextComponent) comboBox.getEditor().getEditorComponent();
        // change the editor's document
        editor.setDocument(new S02BrokenAutoSelection(comboBox.getModel()));
        
        // 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();
            }
        });
    }
}