appletviewer problems

i'm trying to test out a java applet via the UNIX environment using the appletviewer, however i receive this error message and i'd appreciate it if someone can direct me on how to get it to work properly:

Exception in thread "main" java.lang.InternalError: Can't connect to X11 window server using ':0.0' as the value of the DISPLAY variable.
at sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
at
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:125)
at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:63)
at
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:125)
at java.awt.Toolkit$2.run(Toolkit.java:499)
at java.security.AccessController.doPrivileged(Native Method)
at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:492)
at sun.applet.AppletCopyright.(AppletCopyright.java:28)
at sun.applet.AppletViewer.mainInit(AppletViewer.java:1150)
at sun.applet.AppletViewer.main(Compiled Code)

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