Classpath Issue?

Try running by

 java -classpath c:\ class1

Avdej:

Kudos

1 and 2 worked.
3 did not.
3a. did


Avdej, can we use -cp for javac command also? If yes, could you give explain based on above?

Thanks.  You not only provided a good solution but also had time to write and explain it.

Avdej,

I have two questions here:

Question 1:
I also notice that if I do c:\somefolder and then try 3a, it fails,why?
e.g. I navigated to c:\Program Files and did the following two and got the same error

1).java  -cp c:\a\b      folder1.class1
2).java -cp c:\           a.b.folder1.class1

Error got:

C:\>java -cp c:\a\b  folder1.class1
Exception in thread "main" java.lang.NoClassDefFoundError: folder1/class1 (wrong
 name: a/b/folder1/class1)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$100(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)

Question 2:

in java.exe command am I supposed to use -cp only with c:\  like java -cp c:\ something_here
or can I start the class path from anywhere say:   java -cp c:\somedirstructure  rest_of_command

Thanks

Well, the point to understand the issue is:
1. You should have some ROOT directory to build your class structure from, e.g. C:\JavaWork
2. CLASSPATH value points TO THIS root directory and thus allows the JVM (i.e. java.exe) to find the classes you attempt to execute (that is the meaning of the option: '-cp C:\JavaWork')
3. Your classes are organized in packages (simply put: folders) placed underneath the root, i.e. subfolders of C:\JavaWork

Suppose now you have written java class named MyClass (stored as MyClass.java file) and want it to belong to package 'a.b.c'. Then you will have to:
1. Create directory structure: C:\JavaWork\a\b\c (e.g. run: C:\> mkdir C:\JavaWork\a\b\c)
2. Place the following line as the very first line of code into your class code:
    package a.b.c;
3. Save MyClass.java file in directory C:\JavaWork\a\b\c
    (i.e. you should now have file: C:\JavaWork\a\b\c\MyClass.java)

Now you are ready to compile and run your java class:
1. You can compile your class staying anywhere as long as you specify to javac.exe the path where to find the java source file. Thus any of the following will work:
C:\JavaWork> javac .\a\b\c\MyClass.java
C:\> javac .\JavaWork\a\b\c\MyClass.java
D:\someFolder>javac C:\JavaWork\a\b\c\MyClass.java
Simply put: javac.exe (the compiler) is not concerned about any PACKAGES. It just finds and compiles the source file specified.

2. BUT java.exe (the interpreter) behaves in that point very differently: it insists that class to run is named with its fully specified name, i.e: 'a.b.c.MyClass' (in order to distinguish it from some another class, say x.y.z.MyClass)
Now, thus the class name is prefixed with 'a.b.c' then java.exe will try to look for the class file using RELATIVE path .\a\b\c\MyClass.class from some ROOT directory fetched by means of CLASSPATH value provided (i.e.: -cp C:\JavaWork).
Therefore in order to run your classes successfully you have TWO possibilities:
1.
a) Define environment variable named CLASSPATH holding 'C:\JavaWork' entry as well as all other ROOTS of your class file locations  (like PATH for seeking exe files).
b) THEN you can run your class (and any of your classes) just by typing from anywhere:
*>java a.b.c.MyClass

2. Define a special (one-time) classpath value EVERY TIME you run your class. That is what you do typing commands like:
C:\JavaWork> java -cp . a.b.c.MyClass
C:\> java -cp .\JavaWork a.b.c.MyClass
D:\someFolder> java -cp C:\JavaWork a.b.c.MyClass

Hope this helps :-)

Avdej

Avdej,

Kudos to you for 2 things:

2). you took pain to explain to me the concept as one who knows should(in my view, but in real world hardly is the case) giving examples that I always prefer, Examples were very concise!


1). By doing above, you have brought back the old flavor of experts exchange. This in total contrast to present when either I dont see too many responses or if I do, all I see is a 1 liner.

Please watch out for my new  questions that will keep popping thru the week, weekend and beyond
Thanks again and God Bless

Roopesh

yes the site has deteriorated a bit over the years, I find myself contributing a lot less here these days.