ta_console.html
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<TITLE>Implementing a Console Window with a JTextArea Component
(Java Developers Almanac Example)
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<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
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<B><A HREF="../javax.swing.text/pkg.html#JTextArea">JTextArea</A></B><font color="#666666" SIZE="-2">
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<h3>
e987.
Implementing a Console Window with a JTextArea Component</h3>
This example creates a console window using a <code>JTextArea</code> which
shows all output printed to <code>System.out</code> and <code>System.err</code>.
<code>System.out</code> and <code>System.err</code> are replaced with piped io
streams. Two reader threads are created that retrieve the output from
these piped io streams and appends it to the <code>JTextArea</code> component.
<pre>
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class Console extends JFrame {
PipedInputStream piOut;
PipedInputStream piErr;
PipedOutputStream poOut;
PipedOutputStream poErr;
JTextArea textArea = new JTextArea();
public Console() throws IOException {
// Set up System.out
piOut = new PipedInputStream();
poOut = new PipedOutputStream(piOut);
System.setOut(new PrintStream(poOut, true));
// Set up System.err
piErr = new PipedInputStream();
poErr = new PipedOutputStream(piErr);
System.setErr(new PrintStream(poErr, true));
// Add a scrolling text area
textArea.setEditable(false);
textArea.setRows(<font color="#0066ff"><i>20</i></font>);
textArea.setColumns(<font color="#0066ff"><i>50</i></font>);
getContentPane().add(new JScrollPane(textArea), BorderLayout.CENTER);
pack();
setVisible(true);
// Create reader threads
new ReaderThread(piOut).start();
new ReaderThread(piErr).start();
}
class ReaderThread extends Thread {
PipedInputStream pi;
ReaderThread(PipedInputStream pi) {
this.pi = pi;
}
public void run() {
final byte[] buf = new byte[1024];
try {
while (true) {
final int len = pi.read(buf);
if (len == -1) {
break;
}
SwingUtilities.invokeLater(new Runnable() {
public void run() {
textArea.append(new String(buf, 0, len));
// Make sure the last line is always visible
textArea.setCaretPosition(textArea.getDocument().getLength());
// Keep the text area down to a certain character size
int idealSize = <font color="#0066ff"><i>1000</i></font>;
int maxExcess = <font color="#0066ff"><i>500</i></font>;
int excess = textArea.getDocument().getLength() - idealSize;
if (excess >= maxExcess) {
textArea.replaceRange("", 0, excess);
}
}
});
}
} catch (IOException e) {
}
}
}
}
</pre>
The console window is created using
<pre>
try {
new Console();
} catch (IOException e) {
}
</pre>
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Related Examples
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e981. <a class="eglink" href="ta_TextArea.html?l=rel">
Creating a JTextArea Component
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e982. <a class="eglink" href="ta_EditTextArea.html?l=rel">
Modifying Text in a JTextArea Component
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e983. <a class="eglink" href="ta_EnumLines.html?l=rel">
Enumerating the Lines in a JTextArea Component
</a>
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e984. <a class="eglink" href="ta_TabSize.html?l=rel">
Setting the Tab Size of a JTextArea Component
</a>
<br>
e985. <a class="eglink" href="ta_OverrideTab.html?l=rel">
Moving the Focus with the TAB key in a JTextArea Component
</a>
<br>
e986. <a class="eglink" href="ta_Wrap.html?l=rel">
Enabling Word and Line Wrapping in a JTextArea Component
</a>
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See also:
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#Actions%20and%20Key%20Bindings">
Actions and Key Bindings
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#Caret%20and%20Selection">
Caret and Selection
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#Events">
Events
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#JEditorPane">
JEditorPane
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#JFormattedTextField">
JFormattedTextField
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#JTextComponent">
JTextComponent
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#JTextField">
JTextField
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#JTextPane">
JTextPane
</a>
<a class="eglink" href="/egs/javax.swing.text/pkg.html?l=rel#Styles">
Styles
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