How to use classes from .jar files?

Question

I read the Java tutorials on Sun for JAR files, but I still can't find a solution for my problem. I need to use a class from a jar file called jtwitter.jar, I downloaded the file, and tried executing it(since I came to know yesterday that .jar files can be executed by double clicking on them) and Vista gave me an error saying "Failed to load Main-Class Manifest attribute from [path]/jtwitter.jar". The guy who coded the .jar file wants me to import it, but where do I store the .jar file to import it in my code? I tried putting both the .jar file and my .java file in the same directory, didn't work.

The file I'm trying to work for is here: http://www.winterwell.com/software/jtwitter.php

Thanks for putting up with me.

Edit: I'm using JCreator LE. Thanks for the lightning fast responses guys.

Edit: Thanks guys, finally added the .jar file to the classpath and got it working. Thank you.

Answer 1

You need to put the .jar file into your classpath when compiling/running your code. Then you just use standard imports of the classes in the .jar.

Answer 2

Not every jar file is executable.

Now, you need to import the classes, which are there under the jar, in your java file. For example,

import java.util.Map;

If you are working on an IDE, then you should refer its documentation. Or at least specify which one you are using here in this thread. I would definitely enable us to help you further.

And if you are not using any IDE, then please look at javac -cp option.

Answer 3

As workmad3 says, you need the jar file to be in your classpath. If you're compiling from the commandline, that will mean using the -classpath flag. (Avoid the CLASSPATH environment variable; it's a pain in the neck IMO.)

If you're using an IDE, please let us know which one and we can help you with the steps specific to that IDE.

Answer 4

You need to add the jar file in the classpath. To compile your java class:

javac -cp .;jwitter.jar MyClass.java

To run your code (provided that MyClass contains a main method):

java -cp .;jwitter.jar MyClass

You can have the jar file anywhere. The above work if the jar file is in the same directory as your java file.

Answer 5

Let's Say we need to use the class

Classname

that is contained in the jar file

org.example.jar

And your source is in the file

mysource.java

Like this:

import org.example.Classename;
public class mysource {
    public static void main(String[] argv) {
    .....
   }
}

First, as you see, in your code you have to import the classess you need:

import org.example.Classename;

Second, when you compile the source, you have to reference the jar file.

Please note the difference in using

:

and

;

If you are under a unix like operating system:

javac -cp '.:org.example.jar' mysource.java

If you are under windows:

javac -cp .;org.example.jar mysource.java

After this, you obtain the bytecode file

mysource.class

Now you can run this.

If you are under a unix like operating system:

java -cp '.:org.example.jar' mysource

If you are under windows:

java -cp .;org.example.jar mysource