Trouble with jdk?

[Israel]

Ok, I'm using Knoppix 5.1 and everytime I try to compile a source with jdk that has import javax.swing.JOptionPane; I get an error like this:

Exception in thread "main" java.lang.InternalError: Can't connect to X11 window server using ':0' as the value of the DISPLAY variable.
        at sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
        at sun.awt.X11GraphicsEnvironment.access$000(X11GraphicsEnvironment.java:53)
        at sun.awt.X11GraphicsEnvironment$1.run(X11GraphicsEnvironment.java:142)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.awt.X11GraphicsEnvironment.<clinit>(X11GraphicsEnvironment.java:131)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:164)
        at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:68)
        at sun.awt.X11.XToolkit.<clinit>(XToolkit.java:96)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:164)
        at java.awt.Toolkit$2.run(Toolkit.java:821)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:804)
        at javax.swing.UIManager.initialize(UIManager.java:1262)
        at javax.swing.UIManager.maybeInitialize(UIManager.java:1245)
        at javax.swing.UIManager.getUI(UIManager.java:851)
        at javax.swing.JOptionPane.updateUI(JOptionPane.java:1810)
        at javax.swing.JOptionPane.<init>(JOptionPane.java:1773)
        at javax.swing.JOptionPane.showOptionDialog(JOptionPane.java:831)
        at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:645)
        at javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:616)
        at Welcome.main(Welcome.java:5)
root@Me:/home/Israel/Java#

Any suggestions?

[kirol]

You appear to be attempting this while being logged as root. Do it instead under your regular account, from a konsole or xterm under X-xindows. Or at least issue "xhost +" to allow other accounts to access the display (eg root but anyone from any host, really, which is not advisable).

[Israel]

Ah... It ran with X-terminal! Thank you!