Weird white space in a java JFrame

问题

Here is my problem. When i use the following code:

package xyz.lexium.giapb.ui;

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

public class ConsoleWindow extends WindowAdapter implements WindowListener, ActionListener, Runnable {

private JFrame frame;
private JTextArea textArea;
private Thread reader;
private Thread reader2;
private boolean quit;

private final PipedInputStream pin = new PipedInputStream();
private final PipedInputStream pin2 = new PipedInputStream();

public ConsoleWindow() {
    frame = new JFrame("GIAPB - Console");
    Dimension dimension = Toolkit.getDefaultToolkit().getScreenSize();
    int x = (int) ((dimension.getWidth() - frame.getWidth()) / 3);
    int y = (int) ((dimension.getHeight() - frame.getHeight()) / 3);
    frame.setSize(x, y);
    textArea = new JTextArea();
    textArea.setEditable(false);
    JButton button = new JButton("clear");
    button.setBorder(null);
    button.setBackground(Color.BLACK);
    button.setForeground(Color.white);
    frame.getContentPane().setBackground(Color.BLACK);
    frame.getContentPane().setLayout(new BorderLayout());
    frame.getContentPane().add(new JScrollPane(textArea), BorderLayout.CENTER);
    frame.getContentPane().add(button, BorderLayout.SOUTH);
    frame.addWindowListener(this);
    textArea.setBackground(Color.BLACK);
    textArea.setForeground(Color.white);
    textArea.setBorder(null);
    frame.setVisible(true);
    button.addActionListener(this);

    try {
        PipedOutputStream pout = new PipedOutputStream(this.pin);
        System.setOut(new PrintStream(pout, true));
    } catch (java.io.IOException io) {
        textArea.append("Couldn't redirect STDOUT to this console\n" + io.getMessage());
    } catch (SecurityException se) {
        textArea.append("Couldn't redirect STDOUT to this console\n" + se.getMessage());
    }

    try {
        PipedOutputStream pout2 = new PipedOutputStream(this.pin2);
        System.setErr(new PrintStream(pout2, true));
    } catch (java.io.IOException io) {
        textArea.append("Couldn't redirect STDERR to this console\n" + io.getMessage());
    } catch (SecurityException se) {
        textArea.append("Couldn't redirect STDERR to this console\n" + se.getMessage());
    }

    quit = false; // signals the Threads that they should exit

    // Starting two seperate threads to read from the PipedInputStreams
    //
    reader = new Thread(this);
    reader.setDaemon(true);
    reader.start();
    //
    reader2 = new Thread(this);
    reader2.setDaemon(true);
    reader2.start();
}

public synchronized void windowClosed(WindowEvent evt) {
    quit = true;
    this.notifyAll(); // stop all threads
    try {
        reader.join(1000);
        pin.close();
    } catch (Exception e) {
    }
    try {
        reader2.join(1000);
        pin2.close();
    } catch (Exception e) {
    }
    System.exit(0);
}

public synchronized void windowClosing(WindowEvent evt) {
    frame.setVisible(false); // default behaviour of JFrame
    frame.dispose();
}

public synchronized void actionPerformed(ActionEvent evt) {
    textArea.setText("");
}

public synchronized void run() {
    try {
        while (Thread.currentThread() == reader) {
            try {
                this.wait(100);
            } catch (InterruptedException ie) {
            }
            if (pin.available() != 0) {
                String input = this.readLine(pin);
                textArea.append(input);
            }
            if (quit)
                return;
        }

        while (Thread.currentThread() == reader2) {
            try {
                this.wait(100);
            } catch (InterruptedException ie) {
            }
            if (pin2.available() != 0) {
                String input = this.readLine(pin2);
                textArea.append(input);
            }
            if (quit)
                return;
        }
    } catch (Exception e) {
        textArea.append("\nConsole reports an Internal error.");
        textArea.append("The error is: " + e);
    }

}

public synchronized String readLine(PipedInputStream in) throws IOException {
    String input = "";
    do {
        int available = in.available();
        if (available == 0)
            break;
        byte b[] = new byte[available];
        in.read(b);
        input = input + new String(b, 0, b.length);
    } while (!input.endsWith("\n") && !input.endsWith("\r\n") && !quit);
    return input;
}
}

It makes my console, but adds a white line between the text area and the border. How do i remove this

回答1:

The problem is because a JScrollPane also has a border.

In this case you can remove it with:

JScrollPane scroll = new JScrollPane(textArea);
scroll.setBorder(null);

And adding the JScrollPane to your frame as:

frame.getContentPane().add(textArea, BorderLayout.CENTER);

But that will remove the border between the button and the text area

So you need to create a MatteBorder on the top of your JButton:

button.setBorder(BorderFactory.createMatteBorder(1, 0, 0, 0, Color.white));

So it will look like this:

I had forgotten to place how I ran your code in my own main method, because you forgot to add it as part of your MCVE:

It will place the program on the Event Dispatch Thread (EDT)

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new ConsoleWindow();
        }
    });
}

回答2:

You're forgetting that the JScrollPane has a border.

frame.getContentPane().add(new JScrollPane(textArea), BorderLayout.CENTER);

Set it to null.

JScrollPane scrollPane = new JScrollPane(textArea);
scrollPane.setBorder(null);
frame.getContentPane().add(scrollPane, BorderLayout.CENTER);

Another issue: this isn't Swing thread-safe:

public synchronized void run() {
    try {
        while (Thread.currentThread() == reader) {
            try {
                this.wait(100);
            } catch (InterruptedException ie) {
            }
            if (pin.available() != 0) {
                String input = this.readLine(pin);
                textArea.append(input);  // **************
            }
            if (quit)
                return;
        }

        while (Thread.currentThread() == reader2) {
            try {
                this.wait(100);
            } catch (InterruptedException ie) {
            }
            if (pin2.available() != 0) {
                String input = this.readLine(pin2);
                textArea.append(input);  // **************
            }
            if (quit)
                return;
        }
    } catch (Exception e) {
        textArea.append("\nConsole reports an Internal error.");  // **************
        textArea.append("The error is: " + e);  // **************
    }

}

You're making textArea.append(...) calls off of the Swing event thread, and this can cause hard to debug intermittent exceptions to be thrown. Be sure to only append to this text component on the event dispatch thread.

来源：https://stackoverflow.com/questions/41559357/weird-white-space-in-a-java-jframe

标签

java

swing

console

jframe