Please advise me what's wrong with this class declaration:

ExchEngine.java

package engine;

public class ExchEngine {

    public ExchEngine() {

    }
    public static void main(String[] args) {    

        ExchEngine engine=new ExchEngine() ; 

    }
}

When I compile this file, I always get exception:

java.lang.NoClassDefFoundError: test_engine/ExchEngine
Caused by: java.lang.ClassNotFoundException: test_engine.ExchEngine
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Exception in thread "main"

This seems very weird that ExchEngine.java is inside a package and it cannot run itself. Thanks for any help.