Example code for java compiler with a simple GUI

Question

There is no question here (though discussion of the code is welcome).
/* Update 1 */
Now available as a stand alone or webstart app.! The STBC (see the web page*) has its own web page and has been improved to allow the user to browse to a tools.jar if one is not found on the runtime classpath, or in the JRE running the code.
* See [http://pscode.org/stbc/].
/* End: Update 1 */
This simple example of using the JavaCompiler made available in Java 1.6 might be of use to check that your SSCCE is actually what it claims to be!
If an SSCCE claims to display a runtime problem, it should compile cleanly when pasted into the text area above the Compile button. For a compilation problem, the code should show the same output errors seen in your own editor (at least until the last line of the output in the text area).
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.EventQueue;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JLabel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.SwingWorker;
import javax.swing.border.EmptyBorder;
import java.util.ArrayList;
import java.net.URI;
import java.io.ByteArrayOutputStream;
import java.io.OutputStreamWriter;
import javax.tools.ToolProvider;
import javax.tools.JavaCompiler;
import javax.tools.SimpleJavaFileObject;
/** A simple Java compiler with a GUI.  Java 1.6+.
@author Andrew Thompson
@version 2008-06-13
public class GuiCompiler extends JPanel {
  /** Instance of the compiler used for all compilations. */
  JavaCompiler compiler;
  /** The name of the public class.  For 'HelloWorld.java',
  this would be 'HelloWorld'. */
  JTextField name;
  /** The source code to be compiled. */
  JTextArea sourceCode;
  /** Errors and messages from the compiler. */
  JTextArea output;
  JButton compile;
  static int pad = 5;
  GuiCompiler() {
    super( new BorderLayout(pad,pad) );
    setBorder( new EmptyBorder(7,4,7,4) );
  /** A worker to perform each compilation. Disables
  the GUI input elements during the work. */
  class SourceCompilation extends SwingWorker<String, Object> {
    @Override
    public String doInBackground() {
      return compileCode();
    @Override
    protected void done() {
      try {
        enableComponents(true);
      } catch (Exception ignore) {
  /** Construct the GUI. */
  public void initGui() {
    JPanel input = new JPanel( new BorderLayout(pad,pad) );
    Font outputFont = new Font("Monospaced",Font.PLAIN,12);
    sourceCode = new JTextArea("Paste code here..", 15, 60);
    sourceCode.setFont( outputFont );
    input.add( new JScrollPane( sourceCode ),
      BorderLayout.CENTER );
    sourceCode.select(0,sourceCode.getText().length());
    JPanel namePanel = new JPanel(new BorderLayout(pad,pad));
    name = new JTextField(15);
    name.setToolTipText("Name of the public class");
    namePanel.add( name, BorderLayout.CENTER );
    namePanel.add( new JLabel("Class name"), BorderLayout.WEST );
    input.add( namePanel, BorderLayout.NORTH );
    compile = new JButton( "Compile" );
    compile.addActionListener( new ActionListener() {
        public void actionPerformed(ActionEvent ae) {
          (new SourceCompilation()).execute();
    input.add( compile, BorderLayout.SOUTH );
    this.add( input, BorderLayout.CENTER );
    output = new JTextArea("", 5, 40);
    output.setFont( outputFont );
    output.setEditable(false);
    this.add( new JScrollPane( output ), BorderLayout.SOUTH );
  /** Compile the code in the source input area. */
  public String compileCode() {
    output.setText( "Compiling.." );
    enableComponents(false);
    String compResult = null;
    if (compiler==null) {
      compiler = ToolProvider.getSystemJavaCompiler();
    if ( compiler!=null ) {
      String code = sourceCode.getText();
      String sourceName = name.getText().trim();
      if ( sourceName.toLowerCase().endsWith(".java") ) {
        sourceName = sourceName.substring(
          0,sourceName.length()-5 );
      JavaSourceFromString javaString = new JavaSourceFromString(
        sourceName,
        code);
      ArrayList<JavaSourceFromString> al =
        new ArrayList<JavaSourceFromString>();
      al.add( javaString );
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      OutputStreamWriter osw = new OutputStreamWriter( baos );
      JavaCompiler.CompilationTask task = compiler.getTask(
        osw,
        null,
        null,
        null,
        null,
        al);
      boolean success = task.call();
      output.setText( baos.toString().replaceAll("\t", "  ") );
      compResult = "Compiled without errors: " + success;
      output.append( compResult );
      output.setCaretPosition(0);
    } else {
      output.setText( "No compilation possible - sorry!" );
      JOptionPane.showMessageDialog(this,
        "No compiler is available to this runtime!",
        "Compiler not found",
        JOptionPane.ERROR_MESSAGE
      System.exit(-1);
    return compResult;
  /** Set the main GUI input components enabled
  according to the enable flag. */
  public void enableComponents(boolean enable) {
    compile.setEnabled(enable);
    name.setEnabled(enable);
    sourceCode.setEnabled(enable);
  public static void main(String[] args) throws Exception {
    Runnable r = new Runnable() {
      public void run() {
        JFrame f = new JFrame("SSCCE text based compiler");
        f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        GuiCompiler compilerPane = new GuiCompiler();
        compilerPane.initGui();
        f.getContentPane().add(compilerPane);
        f.pack();
        f.setMinimumSize( f.getSize() );
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    EventQueue.invokeLater(r);
* A file object used to represent source coming from a string.
* This example is from the JavaDocs for JavaCompiler.
class JavaSourceFromString extends SimpleJavaFileObject {
  * The source code of this "file".
  final String code;
  * Constructs a new JavaSourceFromString.
  * @param name the name of the compilation unit represented
    by this file object
  * @param code the source code for the compilation unit
    represented by this file object
  JavaSourceFromString(String name, String code) {
    super(URI.create(
      "string:///" +
      name.replace('.','/') +
      Kind.SOURCE.extension),
      Kind.SOURCE);
    this.code = code;
  @Override
  public CharSequence getCharContent(boolean ignoreEncodingErrors) {
    return code;
}Edit 1:
Added..
        f.setMinimumSize( f.getSize() );Edited by: AndrewThompson64 on Jun 13, 2008 12:24 PM
Edited by: AndrewThompson64 on Jun 23, 2008 5:54 AM

Answer 1

kevjava wrote: Some things that I think would be useful:
Suggestions reordered to suit my reply..
kevjava wrote: 2. Line numbering, and/or a line counter so you can see how much scrolling you're going to be imposing on the forum readers.
Good idea, and since the line count is only a handful of lines of code to implement, I took that option. See the [line count|http://pscode.org/stbc/help.html#linecount] section of the (new) [STBC Help|http://pscode.org/stbc/help.html] page for more details. (Insert plaintiff whining about the arbitrary limits set - here).
I considered adding line length checking, but the [Text Width Checker|http://pscode.org/twc/] ('sold separately') already has that covered, and I would prefer to keep this tool more specific to compilation, which leads me to..
kevjava wrote: 1. A button to run the code, to see that it demonstrates the problem that you wish for the forum to solve...
Interesting idea, but I think that is better suited to a more full blown (but still relatively simple) GUId compiler. I am not fully decided that running a class is unsuited to STBC, but I am more likely to implement a clickable list of compilation errors, than a 'run' button.
On the other hand I am thinking the clickable error list is also better suited to an altogether more abled compiler, so don't hold your breath to see either in the STBC.
You might note I have not bothered to update the screenshots to show the line count label. That is because I am still considering error lists and running code, and open to further suggestion (not because I am just slack!). If the screenshots update to include the line count but nothing else, take that as a sign. ;-)
Thanks for your ideas. The line count alone is worth a few Dukes.