Re: [Py4j-users] How to run Stack example in the docs?

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Yeah that seems to be the problem. The following works for me:

Stack.java
-------------------------------------
import java.util.LinkedList;
import java.util.List;

public class Stack {
     private List<String> internalList = new LinkedList<String>();

     public void push(String element) {
         internalList.add(0, element);
     }

     public String pop() {
         return internalList.remove(0);
     }

     public List<String> getInternalList() {
         return internalList;
     }

     public void pushAll(List<String> elements) {
         for (String element : elements) {
             this.push(element);
         }
     }
}
-------------------------------------

StackEntryPoint.java
-------------------------------------
import py4j.GatewayServer;

public class StackEntryPoint {

     private Stack stack;

     public StackEntryPoint() {
       stack = new Stack();
       stack.push("Initial Item");
     }

     public Stack getStack() {
         return stack;
     }

     public static void main(String[] args) {
         GatewayServer gatewayServer = new GatewayServer(new 
StackEntryPoint());
         gatewayServer.start();
         System.out.println("Gateway Server Started");
     }

}
-------------------------------------

I then compiled and ran with:

 > export JARFILE=/usr/local/share/py4j/py4j0.8.2.1.jar
 > javac -cp $JARFILE *.java
 > java -cp .:$JARFILE StackEntryPoint

Thanks a lot for the package! Now that I'm able to I hope to make use of 
it. :p

Just a little. It might be better to use the code as I wrote it instead 
of the way it currently is in the docs. I've used Java in the past, but 
it's been a while and I could never make sense of the error codes nor 
could I make it work without emailing the list. Searching on the 
internet wasn't really that helpful either because the errors were 
fairly generic. I'm pretty sure other Java neophytes might have similar 
issues since they're probably often like me not actually good at Java, 
but have some java that needs to be wrapped in Python. I think making 
this as brain-dead easy as possible will probably help adoption.

In any case, thanks so much for writing this. I'm excited to make use of it!

Cheers,
Thomas

On 12/08/2014 12:36 PM, Barthelemy Dagenais wrote:
> Hi,
>
> thanks for using Py4J!
>
> I believe the problem might be the package. If you copied/pasted the
> code exactly, the Java source files need to be in the appropriate
> directories (e.g., py4j/examples/StackEntryPoint). After compiling the
> classes, you need to specify the fully qualified name of the main
> class when invoking java:
>
> java -cp .:$JARFILE py4j.examples.StackEntryPoint
>
> I suggest though that you just remove the "package py4j.examples;"
> line in both files. You should then be able to compile and run the
> example code.
>
> Alternatively, you can use the StackEntryPoint class that is provided by py4j:
> java -cp $JARFILE py4j.examples.StackEntryPoint
>
> HTH,
> Barthelemy
>
> On Mon, Dec 8, 2014 at 11:39 AM, listserve <tom...@gm...> wrote:
>> Hello,
>>
>> I'm trying to run the code in the docs from here:
>>
>> http://py4j.sourceforge.net/getting_started.html#writing-the-java-program
>>
>> I'm not that experienced with Java so I may very well be making a
>> mistake unrelated to py4j, but I'm unable to run the code regardless.
>> This is what I've done: I saved the Stack code in a file called
>> Stack.java and the other code in StackEntryPoint.java. I compiled it at
>> the command line with the following:
>>
>> JARFILE=/usr/local/share/py4j/py4j0.8.2.1.jar
>> javac -cp $JARFILE *.java
>>
>> That gave no error. I then tried to run it with:
>>
>> java -cp $JARFILE:. StackEntryPoint
>>
>> and I get the following error:
>>
>> Exception in thread "main" java.lang.NoClassDefFoundError:
>> StackEntryPoint (wrong name: py4j/examples/StackEntryPoint)
>>          at java.lang.ClassLoader.defineClass1(Native Method)
>>          at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
>>          at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
>>          at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
>>          at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
>>          at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
>>          at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
>>          at java.security.AccessController.doPrivileged(Native Method)
>>          at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
>>          at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
>>          at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
>>          at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
>>          at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)
>>
>> I am running Linux Mint 17 (which is basically Ubuntu) and the following
>> is my versions of java/javac:
>>
>> $ java -version
>> java version "1.7.0_65"
>> OpenJDK Runtime Environment (IcedTea 2.5.3) (7u71-2.5.3-0ubuntu0.14.04.1)
>> OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode)
>>
>> $ javac -version
>> javac 1.7.0_65
>>
>> Thanks for any help.
>>
>> Cheers,
>> Thomas
>>
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