gentoo portageのSWTはx86_64で問題がある（org.eclipse.swt.gtk.OS.memmoveがないとおこられる）ようなので http://www.eclipse.org/downloads/ -> Other downloads -> SWT Binary and Source -> Linux (x86_64/GTK-2)をダウンロードして以下のようにインストール。

% su
% unzip swt-3.2-gtk-linux-x86_64.zip -d /usr/local/

compile and run a test program.

Test.java:

import org.eclipse.swt.widgets.*;

public class Test {
    public static void main(String[] args) {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setText("Test Shell");
        shell.setSize(200, 200);
        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch())
                display.sleep();
        }
        display.dispose();
    }
}

% export CLASSPATH=$CLASSPATH:/usr/local/swt-M20060629-1905-gtk-linux-x86_64/swt.jar
% export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/swt-M20060629-1905-gtk-linux-x86_64/
% javac Test.java
% java Test

You may also be happy to read following useful documents (notably org.eclipse.swt.widgets in official).

• http://help.eclipse.org/help31/nftopic/org.eclipse.platform.doc.isv/reference/api/overview-summary.html
• http://amateras.sourceforge.jp/cgi-bin/fswiki/wiki.cgi/swt?page=FrontPage

Nihongo unatenakunatta. Koredakara GUI application ha iya nanda.