Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class FormPreviewFrame
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:259)
    at acm.util.JTFTools.readMainClassFromClassPath(JTFTools.java:1092)
    at acm.util.JTFTools.getMainClass(JTFTools.java:461)
    at acm.program.Program.main(Program.java:1320)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

import acm.program.*;

public class hello extends ConsoleProgram{

   public void run(){
       println("Hello World");
   }

}

public static void main(String[] args) {
        new hello().start(args);
    }

import acm.program.*;

public class hello extends ConsoleProgram{

   public void run(){
       println("Hello World");
   }

    public static void main(String[] args) {
        new hello().start(args);
    }

}