package com.example.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.user.client.Window;

public class GwtDragulaTestEntryPoint implements EntryPoint {

	public void onModuleLoad() {
		Window.alert("Hello");
	}
	
}

package com.example.client;

import com.google.gwt.core.client.EntryPoint;

public class GwtDragulaTestEntryPoint implements EntryPoint {

	public void onModuleLoad() {
		Window.alert("Hello");
	}
	
}

Use own window implementation