Running a Java Program

Question

I looked at some other SO questions, didn't find anything that solved my problem... I have a Main.java file (below) and a OthelloLib.jar file without associated source files.

Running javac Main.java fails with

Main.java:8: cannot find symbol
symbol  : class SimplePlayer
location: class Main
        OthelloPlayer p1 = new SimplePlayer();

and a few more errors. SimplePlayer and BetterPlayer are defined in the jar. How do I tell java about this jar? This command: javac -classpath .:OthelloLib.jar -g Main.java doesn't cause an error, but I still don't know how to run the program. If I run java -classpath .:OthelloLib.jar Main, java complains:

Exception in thread "main" java.lang.NoClassDefFoundError: TimeoutException

but TimeoutException.java is in the same directory as Main.java.

I don't know where to look up basic Java stuff like this, so here I am!

public class Main {
  public Main() { }
  public static void main(String[] args) {
    OthelloPlayer p1 = new SimplePlayer();
    OthelloPlayer p2 = new BetterPlayer();
    OthelloObserver o = new OthelloSimObserver();

    // Create an untimed game
    OthelloGame g = new OthelloGame(p1, p2, o);
    System.out.println("Starting game");
    g.run();
  }
}

public Main() { } isn't necessary. Not every class needs a constructor, and since it does nothing, it's just cluttering your code. — Imagist
– Imagist, Commented Sep 18, 2009 at 4:53
legacy code from a class a couple years ago. i'm glad java doesn't require that. :) — Robert Karl
– Robert Karl, Commented Sep 18, 2009 at 6:57

David Z · Accepted Answer · 2009-09-18 03:49:38Z

3

You run

javac -classpath .:OthelloLib.jar Main.java

to compile, then

java -classpath .:OthelloLib.jar Main

In each case the -classpath .:OthelloLib.jar option tells Java where to find SimplePlayer and other classes you need; it doesn't know to look in the JAR file on its own. And you do need to tell both the compiler and the virtual machine where to look for the classes.

EDIT: Looks like you added something about TimeoutException since I wrote this... did you remember to compile TimeoutException.java? And is the TimeoutException.class file in the same directory as Main.class?

answered Sep 18, 2009 at 3:49

David Z

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2 Comments

Robert Karl Over a year ago

i tried that second command... java complains about a different problem... seems like it found the classes buried in the jar, though.

David Z Over a year ago

Ah... yeah, at this stage I'd suggest doing things using a text editor and the command line. Once you understand the process, then head back to Eclipse.

Stefan Kendall · Accepted Answer · 2009-09-18 03:51:12Z

2

Note: You can do all this within a good IDE like eclipse or netbeans by adding the library to your project. The rest gets handled automagically.

answered Sep 18, 2009 at 3:51

Stefan Kendall

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Comments

Dale · Accepted Answer · 2009-09-18 03:51:19Z

2

Have you set a reference to OthelloLib.jar or invoking the javacompiler with the library as a parameter?

java -classpath .:OthelloLib.jar -g Main

answered Sep 18, 2009 at 3:51

Dale

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Winston Chen · Accepted Answer · 2009-09-18 03:58:09Z

1

Did you import all the libraries?

like

import a.b.c. OthelloPlayer;

edited Sep 18, 2009 at 3:58

answered Sep 18, 2009 at 3:51

Winston Chen

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pythonquick · Accepted Answer · 2009-09-18 03:50:29Z

0

Did you specify the classpath when you call your program?

Something like the following might work:

java -cp .:OthelloLib.jar Main

answered Sep 18, 2009 at 3:50

pythonquick

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