试图从System.out.println迁移到Swing的Java学徒

Question

I'm finally trying to migrate my old console programs to Swing, to make distribution to my friends easier. To this end, I'm trying to write a class ConsoleFrame that I can extend instead of JFrame, that will allow me to interface my old code with Swing as effortlessly as possible. out(String) appears to be working, but inln() has me stumped.

//Imports not included
public class ConsoleFrame extends JFrame
{
    protected JTextField in;
    protected JTextArea out;

    public ConsoleFrame(){
        this("Console Frame", 80, 10);
    }
    public ConsoleFrame(int cols){
        this("Console Frame", cols, 10);
    }
    public ConsoleFrame(int cols, int rows){
        this("Console Frame", cols, rows);
    }
    public ConsoleFrame(String title){
         this(title, 80, 10);
    }
    public ConsoleFrame(String title, int cols, int rows){
        in = new JTextField();
        in.setEditable(true);
        in.setColumns(cols);

        out = new JTextArea();
        out.setEditable(false);
        out.setColumns(cols);
        out.setRows(rows);
        out.setWrapStyleWord(true);

        setTitle(title);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        add(in, BorderLayout.PAGE_END);
        add(out, BorderLayout.PAGE_START);
        pack();
    }

    protected void out(String o) {
        out.append(o);
    }
    protected void outln(String o) {
            out(o + BIO.$ln);    //BIO.$ln == System.getProperty("line.separator")
    }

    /*
     * This is supposed to halt execution until the user presses enter, then return the text entered in the JTextField named in.
     */
    protected String inln() {
        in.setEnabled(true);
        KeyListener enter = new KeyListener() {
            @Override
            public void keyTyped(KeyEvent paramKeyEvent) {
                if(paramKeyEvent.getKeyCode() == KeyEvent.VK_ENTER) {
                     if(in.hasFocus()) {
                         in.setEnabled(false);
                     }
                }
            }
            @Override public void keyPressed(KeyEvent paramKeyEvent) {}
            @Override public void keyReleased(KeyEvent paramKeyEvent) {}    
        };
        in.addKeyListener(enter);
        while(true){    //This loop is intended to interrupt flow until in.isEnabled()==false, which will only happen when the enter key is typed.
            if(in.isEnabled()==false){
                String result = in.getText();
                in.setText("");
                in.setCaretPosition(0);
                this.removeKeyListener(enter);
                in.setEnabled(true);
                return result;
            }
        }
    }
}

Tester program:

public class Tester extends ConsoleFrame
{
    public static void main(String[] args) {
        new Tester();
    }
    public Tester() {
        super("Test", 60, 30);
        out(inln());
    }
}

Answer 1

Don't know if it will fix your problem, but you should NOT be using a KeyListner.

JTextField was designed to use an ActionListener to handle the Enter key.

Answer 2

A bit of debugging shows the key code is 0x0 always. Replacing keyTyped with the following code seems to work;

public void keyTyped(KeyEvent paramKeyEvent) {
    if (paramKeyEvent.getKeyChar() == '\n') {
        if(in.hasFocus()) {
            in.setEnabled(false);
        }
    }
}

EDIT: I'm not saying this is a solution I'm overly happy with, but it seems to do the trick.

Answer 3

You are adding the keyListener to the frame, and not the in textfield. Therefore, the event will always be captured by the textfield and never propagated up to the Frame. This is why you are not receiving the event.

Answer 4

That inln code looks racy to me. To make it more robust:

• Change your code so that the actual program runs in a thread different from the event dispatch thread (I am not sure if this is already true). SwingUtilities.isEventDispatchThread should return false when called from your test program.

• Use SwingUtilities.invokeLater in your output methods so that the actual output will happen on the event dispatch thread asynchronously.

• in inln() , use synchronization and SwingUtilities.invokeAndWait to initialize your key listener stuff (or use an ActionListener as already stated). Then use Object.wait() and Object.notify() instead of your busy-waiting loop while waiting for input (laptop users' batteries will thank you for that, and the Task Manager which will no longer show 100% CPU usage).

---

Sorry, Here is the (tested and working) code for you:

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

public class ConsoleFrame extends JFrame
{
    private Object lock = new Object();
    private String enteredText = null;

    protected JTextField in;
    protected JTextArea out;

    public ConsoleFrame(){
        this("Console Frame", 80, 10);
    }
    public ConsoleFrame(int cols){
        this("Console Frame", cols, 10);
    }
    public ConsoleFrame(int cols, int rows){
        this("Console Frame", cols, rows);
    }
    public ConsoleFrame(String title){
         this(title, 80, 10);
    }
    public ConsoleFrame(String title, int cols, int rows){
        in = new JTextField();
        in.setEditable(true);
        in.setColumns(cols);

        ActionListener enter = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                in.setEnabled(false);
                synchronized(lock) {
                    enteredText = in.getText();
                    lock.notifyAll();
                }
                in.setText("");
            }
        };
        in.addActionListener(enter);

        out = new JTextArea();
        out.setEditable(false);
        out.setColumns(cols);
        out.setRows(rows);
        out.setWrapStyleWord(true);

        setTitle(title);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        add(in, BorderLayout.PAGE_END);
        add(out, BorderLayout.PAGE_START);
        pack();
    }

    protected void out(final String o) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                out.append(o);
            }
        });
    }

    protected void outln(String o) {
            out(o + System.getProperty("line.separator"));
    }

    /*
     * This is supposed to halt execution until the user presses enter, then return the text entered in the JTextField named in.
     */
    protected String inln() {
        SwingUtilities.invokeLater(new Runnable() { 
            @Override
            public void run() {
                in.setEnabled(true);
            }
        });
        synchronized(lock) {
            enteredText = null;
            while (enteredText == null) {
                try {
                    lock.wait();
                } catch (InterruptedException ex) {}
            }
            return enteredText;
        }
    }
}