Difference between wildcard(*.java or source files list) & individual source file compilations.

[Lokesh Lov]

1. I have two classes Car and BMW defined in Car.java and BMW.java source files respectively in current working directory say "workspace".

2. Car.java file content looks like
------------------------------------------
package automob;
public abstract class Car {
// members & behaviours
}
------------------------------------------

3. BMW.java file content looks like(this class falls in default package)
------------------------------------------
import automob.Car;
class BMW extends Car {
// BMW specific implementation
}
------------------------------------------

4. CLASSPATH is set to current directory "."

My observation is when I am compiling these two files as

$ javac Car.java BMW.java
(or)
$ javac *.java

compilation succeeded, but when trying to compile BMW.java file compilation fails because Car.class should be in sub-directory(package) "automob".

So, can anybody tell me how the following commands are different?
$ javac *.java // compilation succeeded

$ javac BMW.java // compilation fails

[K. Tsang]

Welcome to the Ranch.

What folder are you running javac command. If your Car class is in a package and your BMW class is not then when you do
javac *.java
should only compile the one java source in that directory.
Similar when you compile just the BMW class, it "should" able to look up or find its dependent class (eg Car) and compile that too.

Does your file structure looks like:
>BMW.java
>automob
|_Car.java

Try running the "javac BMW.java" command in the folder you have BMW.java

[Lokesh Lov]

Thank you, #K. Tsang

my current working directory is workspace, and these two source files(Car.java and BMW.java) are in this directory only(not placed in appropriate directory structure).
When I issues ls command(I use linux) files are listed as.

workspace$ ls
Car.java     BMW.java

BMW class has no package declaration, and Car class belongs to automob package, so it should be placed in automob directory to work. But I observed that when I tried

workspace$ javac *.java
(or)
workspace$ javac Car.java BMW.java

command to compile, even Car.java is not in automob directory, compilation succeeded.
When I issues "ls" command(I use linux) files are listed as.

workspace$ ls
Car.class    Car.java     BMW.class     BMW.java

I want to know how compiler can resolve Car.class from BMW.class definition(which is not placed in appropriate directory automob).

[K. Tsang]

Ah that's why. Your Car class isn't in the proper folder structure. This is why when you do "javac BMW.java" it failed because it expects the Car.java file in the automob folder which is not there.

You should create a "automob" folder and put the Car file inside. Do the javac command at the BMW file level. This way "javac *.java" or "javac BMW.java" will produce the same result. When compiled, the Car.class should be in the automob folder.