Java newbie: Swing and displaying ASCII files

Question

G'day all,

I have an application which needs to display an ASCII file of 15 lines in a Swing component that cannot be edited by the user.

Below is my code which reads the ASCII file byte by byte. My thanks to the helpful commenters who explained that a JTextArea.setEditable(false) would be appropriate in Swing.

However, my code merely displays a string of numbers, when I personally made the ASCII file to be something quite different. Does anyone know what I am doing wrong and how to get the ASCII characters themselves to display?

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

public class LoadMap extends JFrame {
    public LoadMap() throws IOException {
        FileInputStream fIn = new FileInputStream("map.srn");
        BufferedReader rd = new BufferedReader(new InputStreamReader(fIn, "US-ASCII"));
        String map = "";
        JTextArea mapArea = new JTextArea(15, 50);

        try {
            int c;
            while ((c = rd.read()) != -1) {
                map= map + c;
            }
        } finally {
            if (rd != null) {
                rd.close();
            }
        }
        mapArea.setText(map);
        mapArea.setEditable(false);
        add(mapArea);
        pack();
        setVisible(true);
    }
}

Answer 1

Use a JTextArea and call

setEditable(false);

to stop the user being able to edit the data

I've just read your code through and realise that's not a comprehensive enough answer. You can't do "+" on a label. What you need to do is read the text in first and store it somewhere, then call

setText(yourTextAsString);

on your text component on screen (for which I'd still use the JTextArea), and you need to add the text area to the frame, so your code would look something like:

public LoadMap() {
     String data = // read your data
     JTextArea textArea = new JTextArea();
     textArea.setText(data);
     textArea.setEditable(false);
     setLayout(new GridLayout());
     add(textArea);
     pack();
     setVisible(true);
}

I would suggest reading the Swing tutorial to get some more info on using Swing components

Answer 2

Use a JTextArea and call setEditable(false).

http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/text/JTextComponent.html#setEditable(boolean)

Answer 3

You could construct a String inside the loop, and then put the string into JLabel when you've finished.

Answer 4

This makes me feel like Captain Obvious, but still: just load the entire text first, and then build the label using the desired text. Or, as other posters rightly suggest, use a JTextArea since its more well-suited for multiline content.

Answer 5

You could use a JTextArea and set it to read only:

jtextarea.setEditable(false);

Answer 6

A JLabel will not display line breaks (unless you use HTML). So as the others wrote, use a text area.

However, there's another hidden problem with your code: you don't specify the file's encoding, which means the file contents may be garbled if it contains non-ASCII characters and its encoding does not match Java's platform default. To fix this, do not use FileReader. Instead, use a FileInputStream and wrap it in an InputStreamReader, specifying the encoding in its constructor.

Answer 7

Here:

String map = "";
int c;
while ((c = rd.read()) != -1) {
    map= map + c;
}

What you're doing it appending int's to the string.

You should cast them to char instead.

int c;
while ((c = rd.read()) != -1) {
    map= map + ( char ) c;
}

You can see much better patterns in these questions.

http://stackoverflow.com/questions/326390/how-to-create-a-java-string-from-the-contents-of-a-file

http://stackoverflow.com/questions/181634/simplest-efficient-ways-to-read-binary-and-ascii-files-to-string-or-similar-in-v/324792#324792 ( see java part )