CODEWITHSUNDEEP
javajarpackage
Aiden Strydom
Aiden Strydom

Reputation: 1218

Cant Compile jar if added to a package

Problem: I wrote a hello world java program, compiled and created a jar file of it - PERFECT, no problems there.

I now added the following to the top of the source code

package za.ac.uj.csc2a;

saved the code, place all the files in the right directories and every time i compile with this batch file

del *.class
del *.jar
del *.txt

echo compiling HelloWorld.java.....

javac HelloWorld.java

javap -c HelloWorld.class > ByteCode.txt

jar cfe HelloWorld.jar HelloWorld HelloWorld.class

java -jar za.ac.uj.csc2a.HelloWorld.jar

i get, 

Error: Unable to acces jarfile za.ac.uj.csc2a.HelloWorld.jar

Any Advice....

Here is the final bat file that works

del *.class
del *.jar
del *.txt
RD /Q /S bin

echo compiling HelloWorld.java.....

MD bin

javac -d bin za/ac/uj/csc2a/HelloWorld.java
javap -c bin/za/ac/uj/csc2a/HelloWorld.class > ByteCode.txt
jar cfe HelloWorld.jar za.ac.uj.csc2a.HelloWorld -C bin .
java -jar HelloWorld.jar
pause

thanks alot

Aiden

Upvotes: 2

Views: 247

Answers (6)

user unknown
user unknown

Reputation: 36250

Your jar is named Helloworld.jar:

 jar cfe HelloWorld.jar HelloWorld HelloWorld.class

But you call it with the package name as prefix to the jar:

 java -jar za/ac/uj/csc2a/HelloWorld.jar

 java -jar HelloWorld.jar

should be right.

Normally, you put your classes and sources in different directories, if you use packages. A typical tree looks like 

proj
|-- src
|   |-- za
|       |-- ac
|           `-- HelloWorld.java
|-- bin
    |-- za
        |-- ac
            `-- HelloWorld.class

You can move to the src-directory, and compile with: 

 javac -d ../bin za/ac/HelloWorld.java

(reduced the package/path length for convenience) This will produce the directory structure in bin if needed (or often classes)

Then, to jar the whole thing with the correct directory structure, you change to proj, and issue:

jar cfe HelloWorld.jar za.ac.HelloWorld -C bin .

The dot stands for the whole directory. 

jar -help

will tell you more options. To create a runnable jar you need a manifest too. Else you can start your app: 

java -cp HelloWorld.jar za.ac.HelloWorld

(shortened the path a bit again).

Note, that the structure of the directory has to reflect the package declaration. You can't omit a part (za), and step into the next directory (ac). The class to run is za.ac.HelloWorld and therefor it is searched for in za/ac/ - no matter whether in the file system or in the jar.

If you learn to issue the commands from the right base, it is easy. If not, you'll get years of trial and error.

For a jar which can be startet with java -jar, you need a manifest. A template is generated by the jar command. There you add

Main-Class: za.ac.HelloWorld

with a following blank line. Again: the whole name with package is needed. Main-Class can't be written as Mainclass. HelloWorld must not be followed by .class or .java - common mistakes! But as you know, you may use the -e switch to specify the main class, but again: Include the package name.

Upvotes: 1

DNA
DNA

Reputation: 42617

You are creating a jar called HelloWorld.jar:

jar cfe HelloWorld.jar HelloWorld HelloWorld.class

Then trying to invoke a different jar name (za.ac.uj.csc2a.HelloWorld.jar):

java -jar za.ac.uj.csc2a.HelloWorld.jar

They need to be consistent

Upvotes: 0

aioobe
aioobe

Reputation: 421110

The -jar option accepts a filename, not a class.

You should just do 

java -jar HelloWorld.jar

But keep in mind that you need to specify a main-class in the manifest file you you want it to execute using the -jar option.

The manifest file should look like

Main-Class: za.ac.uj.csc2a.HelloWorld

and you include it with the m option on the jar command.

Also, it seems that you're adding the .class-file in the root of the jar file. It should be in the za.ac.uj.csc2a directory

If you don't want to go with a manifest file, you could also launch it like this (perhaps that's what you're trying):

java -cp HelloWorld.jar za.ac.uj.csc2a.HelloWorld

Upvotes: 2

Jesper
Jesper

Reputation: 206916

place all the files in the right directories

Are you sure about that? Because if your code is in a package za.ac.uj.csc2a then your source file must be in a directory za\ac\uj\csc2a, you should compile it with a command like this:

javac za\ac\uj\csc2a\HelloWorld.java

and also inside the JAR file it should be inside a directory with that name, so you should package the JAR with a command like this:

jar cf HelloWorld.jar za\ac\uj\csc2a\HelloWorld.class

You will only be able to execute it with java -jar if it is an executable jar, in other words, if you add a manifest file to the JAR with a correct Main-Class attribute. If you didn't do this, you should be able to run it from the JAR with:

java -cp HelloWorld.jar za.ac.uj.csc2a.HelloWorld

See Packaging Programs in JAR Files for details on how to package your app in an executable JAR file so that you can execute it with

java -jar HelloWorld.jar

Upvotes: 0

Rocky
Rocky

Reputation: 951

You should actually call java -jar HelloWorld.jar instead of java -jar za.ac.uj.csc2a.HelloWorld.jar

Upvotes: 0

JB Nizet
JB Nizet

Reputation: 692003

Your jar file is named HelloWorld.jar, not za.ac.uj.csc2a.HelloWorld.jar. So obviously, java doesn't find it.

The jar file contents must respect the package hierarchy, so inside the jar file, the HelloWorld.class must be in the folder za/ac/uj/csc2a.

Upvotes: 0

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