Question

Recently I have written a pair of applications with JAVA/Swing with a simple GUI:

• A JScrollPane
• In the first application, there is a JTextArea inside the JScrollPane, and in the second one there is a JTable.

They look OK, they work OK. Until I executed then on a Windows 7 tablet (HP Slate). They both look empty, with a tiny symbol in the middle. This picture shows how the first application (the JTextArea one) looks over the tablet:

What’s the problem here and how can I solve it?

I’m showing the code, but since it looks fine when using a computer, I guess this is not the problem:

import java.io.*;
import java.net.*;

import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import java.awt.Dimension;
import java.awt.Toolkit;

import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.text.DefaultCaret;

class EstacionBase extends JFrame{
    private static final long serialVersionUID = 1L;

private static final String logFile = "log.txt";

private DateFormat df;
private FileWriter logWriter;

private Socket sisnetSocket;
private ServerSocket serverSocket;
private Socket clientSocket;
private BufferedWriter outToPlane;
private BufferedWriter outToDataServer;
private BufferedReader inputFromDataServer;
private JTextArea console;

private boolean terminated;

public EstacionBase() {
    setTitle("Base station");
    createGUI();
    pack();
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLocationRelativeTo(null);
    setVisible(true);

    try{
        df = new SimpleDateFormat ("[hh:mm:ss]");
        logWriter = new FileWriter(System.getProperty("user.dir") + "\\" + logFile, true);
        serverSocket = new ServerSocket(PORT); // A socket I use for listening for connections
    } catch(IOException e){
        JOptionPane.showMessageDialog(this, e.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
    }

    //mainLoop(); // doing some stuff

    try{
        logWriter.close();
        serverSocket.close();
    } catch(IOException e){
        JOptionPane.showMessageDialog(this, e.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
    }
}

private void createGUI() {
    setLayout(new GridBagLayout());
    GridBagConstraints c = new GridBagConstraints();
    c.gridx = 0;
    c.gridy = 0;
    c.fill = GridBagConstraints.BOTH;

    console = new JTextArea(40, 80);
    JScrollPane scroll = new JScrollPane(console);
    DefaultCaret caret = (DefaultCaret) console.getCaret();
    caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE); // Autoscroll
    console.setText("Welcome to base station");
    console.setEditable(false);
    console.setVisible(true);
    add(scroll, c);
}

private void writeToConsole(String msg) throws IOException{
    Date now = new Date();
    String timeStr = df.format(now);
    console.append("\n");
    console.append(timeStr + " " + msg);
    writeToLogFile(msg, timeStr);
}

private void writeToLogFile(String msg, String timeStr) throws IOException{
    logWriter.write(timeStr + " " + msg + CRLF);
        logWriter.flush();
    }

    public static void main(String[] arg) {
        EstacionBase frame = new EstacionBase();
    }

}

Answer 1

This is a GridBagLayout problem; I’m not sure of the optimal fix, but it works fine with the default JFrame layout, BorderLayout.CENTER. Functionally, these three layouts have similar effects:

• BorderLayout.CENTER: the default for JFrame#add().

• GridLayout(): one column, one row, no gaps.

• GridBagLayout(): the default GridBagConstraints() has all fields set to default values.

As an aside, Swing GUI objects should be constructed and manipulated only on the event dispatch thread.