Java: TextAreaDemo

/*
 * TextAreaDemo.java requires no other files.
 */

import javax.swing.*;
import java.util.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import java.awt.event.ActionEvent;
import javax.swing.text.BadLocationException;
import javax.swing.GroupLayout.*;


public class TextAreaDemo extends JFrame
        implements DocumentListener {
    
    private JLabel jLabel1;
    private JScrollPane jScrollPane1;
    private JTextArea textArea;
    
    private static final String COMMIT_ACTION = "commit";
    private static enum Mode { INSERT, COMPLETION };
    private final List<String> words;
    private Mode mode = Mode.INSERT;
    
    
    
    public TextAreaDemo() {
        super("TextAreaDemo");
        initComponents();
        
        textArea.getDocument().addDocumentListener(this);
        
        InputMap im = textArea.getInputMap();
        ActionMap am = textArea.getActionMap();
        im.put(KeyStroke.getKeyStroke("ENTER"), COMMIT_ACTION);
        am.put(COMMIT_ACTION, new CommitAction());
        
        words = new ArrayList<String>(5);
        words.add("spark");
        words.add("special");
        words.add("spectacles");
        words.add("spectacular");
        words.add("swing");
    }
    
    
    private void initComponents() {
        jLabel1 = new JLabel("Try typing 'spectacular' or 'Swing'...");
        
        textArea = new JTextArea();
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        textArea.setColumns(20);
        textArea.setLineWrap(true);
        textArea.setRows(5);
        textArea.setWrapStyleWord(true);
        
        jScrollPane1 = new JScrollPane(textArea);
        
        GroupLayout layout = new GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        
        //Create a parallel group for the horizontal axis
        ParallelGroup hGroup = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
        //Create a sequential and a parallel groups
	SequentialGroup h1 = layout.createSequentialGroup();
        ParallelGroup h2 = layout.createParallelGroup(GroupLayout.Alignment.TRAILING);
        //Add a scroll panel and a label to the parallel group h2
	h2.addComponent(jScrollPane1, GroupLayout.Alignment.LEADING, GroupLayout.DEFAULT_SIZE, 212, Short.MAX_VALUE);
        h2.addComponent(jLabel1, GroupLayout.Alignment.LEADING, GroupLayout.DEFAULT_SIZE, 212, Short.MAX_VALUE);
        
	//Add a container gap to the sequential group h1
	h1.addContainerGap();
        // Add the group h2 to the group h1
	h1.addGroup(h2);
        h1.addContainerGap();
        //Add the group h1 to hGroup
	hGroup.addGroup(Alignment.TRAILING,h1);
        //Create the horizontal group
	layout.setHorizontalGroup(hGroup);
        
	//Create a parallel group for the vertical axis
        ParallelGroup vGroup = layout.createParallelGroup(GroupLayout.Alignment.LEADING);
        //Create a sequential group
	SequentialGroup v1 = layout.createSequentialGroup();
        //Add a container gap to the sequential group v1
	v1.addContainerGap();
        //Add a label to the sequential group v1
	v1.addComponent(jLabel1);
        v1.addPreferredGap(LayoutStyle.ComponentPlacement.RELATED);
        //Add scroll panel to the sequential group v1
	v1.addComponent(jScrollPane1, GroupLayout.DEFAULT_SIZE, 100, Short.MAX_VALUE);
        v1.addContainerGap();
        //Add the group v1 to vGroup
	vGroup.addGroup(v1);
        //Create the vertical group
	layout.setVerticalGroup(vGroup);
        pack();
        
    }
    // Listener methods
    
    public void changedUpdate(DocumentEvent ev) {
    }
    
    public void removeUpdate(DocumentEvent ev) {
    }
    
    public void insertUpdate(DocumentEvent ev) {
        if (ev.getLength() != 1) {
            return;
        }
        
        int pos = ev.getOffset();
        String content = null;
        try {
            content = textArea.getText(0, pos + 1);
        } catch (BadLocationException e) {
            e.printStackTrace();
        }
        
        // Find where the word starts
        int w;
        for (w = pos; w >= 0; w--) {
            if (! Character.isLetter(content.charAt(w))) {
                break;
            }
        }
        if (pos - w < 2) {
            // Too few chars
            return;
        }
        
        String prefix = content.substring(w + 1).toLowerCase();
        int n = Collections.binarySearch(words, prefix);
        if (n < 0 && -n <= words.size()) {
            String match = words.get(-n - 1);
            if (match.startsWith(prefix)) {
                // A completion is found
                String completion = match.substring(pos - w);
                // We cannot modify Document from within notification,
                // so we submit a task that does the change later
                SwingUtilities.invokeLater(
                        new CompletionTask(completion, pos + 1));
            }
        } else {
            // Nothing found
            mode = Mode.INSERT;
        }
    }
    
    private class CompletionTask implements Runnable {
        String completion;
        int position;
        
        CompletionTask(String completion, int position) {
            this.completion = completion;
            this.position = position;
        }
        
        public void run() {
            textArea.insert(completion, position);
            textArea.setCaretPosition(position + completion.length());
            textArea.moveCaretPosition(position);
            mode = Mode.COMPLETION;
        }
    }
    
    private class CommitAction extends AbstractAction {
        public void actionPerformed(ActionEvent ev) {
            if (mode == Mode.COMPLETION) {
                int pos = textArea.getSelectionEnd();
                textArea.insert(" ", pos);
                textArea.setCaretPosition(pos + 1);
                mode = Mode.INSERT;
            } else {
                textArea.replaceSelection("\n");
            }
        }
    }
   
    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                //Turn off metal's use of bold fonts
                UIManager.put("swing.boldMetal", Boolean.FALSE);
                new TextAreaDemo().setVisible(true);
            }
        });
    }
}