Stanford's Karel the Robot throws NullPointerException

Question

I have started taking the course Programming methodology(CS106A) available at stanford website. But I am not able to start the Stanford Karel in it.

I am using eclipse indigo classic 3.7.1 and Windows 7 64 bit OS..

I wrote the following code:

import stanford.karel.*;

public class CollectNewspaperKarel extends SuperKarel {
    // You fill in this part
    public void run(){
      move();
      move();
    }
}

It gives the error

Exception in thread "main" java.lang.NullPointerException
   at acm.program.Program.main(Program.java:917)
   at stanford.karel.Karel.main(Karel.java:202)

I followed some instructions given here but then got a blank screen as the output.

The assignment1 of stanford can be found here, and karel the robot of stanford is available here

Answer 1

You are getting that error because you are not using the Eclipse version provided by the Stanford University. For more detailed information,

Edit: Deleted this link as it is not working anymore.

Edit:

Since the above link is not working anymore, I wrote the following steps. Since I am not using Karel anymore, if someone followed through the guide and can make any corrections, please comment of edit this answer.

Instructions:

a.Visit Stanford website and download the following softwares

1. Eclipse for windows from Stanford
2. Java Jre software

b.Install the softwares.

c.Download Assignment1.zip from Assignments tab.

d.Install the Assignment into Eclipse.

Now, we are done with the setup guide. Lets discuss about the common problems:

Problems:

Problem 1 : Blank Screen

This means, you installed the latest version of the Sun Java JRE software. The solution to this problem is I. Uninstall all the JRE software versions except the one downloaded from the Stanford Website.

OR, try this

a.Open Eclipse Software.

b.In the Menu toolbar, Click Window and then Click Preferences

c. Follow these simple steps:

1. In the Preferences window, Click Java.
2. In the drop down section shown under Java, click Installed JREs.
3. The JRE we downloaded from the Stanford website is the jre6 update 2. So select it. Only jre6 is compatible with the stanford eclipse software. So, uncheck all the other versions installed in your system and check the jre6 box as shown in the image below.
4. Click Ok. 5.Run the program. Now you can see that the output is fine.

Problem 2 : Error

When you run the program, you may sometimes notice this error.

*

*Exception in thread "main" java.lang.NullPointerException
    at acm.program.Program.main(Program.java:917)
    at stanford.karel.Karel.main(Karel.java:202)*

*

This means you did not download the Stanford Eclipse Software and you are using the latest version of the Eclipse that you have downloaded from the Eclipse website. So follow the detailed guide that I mentioned above. Everything will work fine.

Answer 2

A lot the times this can be a result of not changing things like build settings. Check your configuration settings in eclipse.

Answer 3

hello bhuwansahni though I have written an answer before, but now I am writing the entire process to run Karel in any eclipse version.

1. Create a new project in your Eclipse (File-----> New-----> Java Project)

2. Load your assignment in the Created Project.

   step a:- Extract Assignment 1 in your desired folder.

   step b:- import the assignment (File-----> Import----->General-----> Files system-----> browse your folder and complete the importing.)

3. Now run it in a different way (Run-----> Run Configurations-----> )

   Step a:- Under Java Applet Create New Configuration.

   Step b:- Under Main write the Main Class stanford.karel.Karel

   Picture for **Step b of Step 3] https://i.stack.imgur.com/0LpI3.jpg

   Step c:- Under (x)= Arguments in Program Arguments write code=CollectNewspaperKarel

   Picture for **Step b of Step 3] https://i.stack.imgur.com/alIss.jpg

   Step d:- Apply and Run

4. Now Here comes the Karel the most Lovable Robot.

   Picture for **Step 3] URL:- (i.stack.imgur.com/d8SAa.jpg) put http:// in front to see it... as here I can't post more than two hyperlinks.

Answer 4

Be sure to use JRE6 and not JRE7.

To do that, you do not need to uninstall JRE7 and install JR6. Just install JRE6. In Eclipse, go to Window --> Preferences --> Java --> Installed JREs. Add the path to JRE6. In Run configuration, select Alternate JRE to jre6.

Answer 5

Maybe it is with Juno Eclipse only but I also had to check the "Include inherited mains when searching for a main class" checkbox in the Main tab in the Run Configurations... dialog.

Answer 6

public class StoneMasonKarel extends SuperKarel {
    public static void main(String[] args) {
        stanford.karel.Karel.main(new String[] { "code="
                + StoneMasonKarel.class.getCanonicalName() });
    }
    public void run() {
    }
}

You need Java6.

In Eclipse:

1. Project >> Settings >> Java Compiler: Select 1.6
2. Right click Run button >> Run Configuration >> JRE Tab >> Alertnative JRE: Select/add your Java 6 path

Then I implement a main method for each project like the one above. For each rename StoneMasonKarel.class to whatever your class name is.

Answer 7

As of writing this post, I just figured it out and I wrote an entire blog post to explain it further. Here's a snippet:

"So here’s the thing. You’ve got to download OpenJDK6 from the Ubuntu Software Center (USC). You probably already have it on your computer, but you should still check out the USC just in case. Once you have that, go back to Eclipse and open Windows, Preferences, which should open right to “Installed JRE”."

More at: http://bakaripace.wordpress.com/2014/06/21/how-to-set-up-stanfords-karel-in-ubuntu-14-04-lts/

Answer 8

https://support.apple.com/kb/DL1572?locale=en_US&viewlocale=en_US

download jre 6 for OSx on this website :)

Answer 9

I had the same problem, I am running Eclipse Neon on Ubuntu, not the Stanford Eclipse. I had incorrectly set the Argument's tab. Make sure you set your run configuration correctly.

Answer 10

Just install JRE6 and it will work. It worked for me without doing anything. Just intal JRE6 and compile with that. Change the compiler type in project>properties>compiler