SCJP chapter 10 : Development

[Swapnil Suryakant Prabhavalkar]

Hi all,

There is one question in self-test of K&B book which I would like to discuss with you.

The question is :

Given the following directory structure:

test - |
|- GetJar.java
|
|- myApp - |
|-Foo.java

And given the contents of GetJar.java and Foo.java

3. public class GetJar{
4.    public static void main(String[] args){
5.        System.out.println(myApp.Foo.d);
6.    }
7. }

3. package myApp;
4. public class Foo{public static int d = 8;}

If the current directory is "test", and myApp/Foo.class is placed in a JAR file called MyJar.jar located in the test, which set(s) of command will compile GetJar.java and produce the output 8?

And correct answer given in the book is :

javac -classpath MyJar.jar GetJar.java
java GetJar


Now , as per my understanding java compiler won't search for files in current directory if it is not specified in classpath with (.). Then if we are not specifying (.) in classpath, how compiler is able to find GetJar.java?


This may sound like a silly question bu t as I am using IDE a lot for development and I have never used command prompt for compiling and executing java files, I am confused.

Could you please help me out?

[Ankit Garg]

-classpath is used to specify the path where the compiler will look for .class files required to compile the passed .java file. Since in the command only GetJar.java is specified then the compiler will look for GetJar.java in the current directory. The command is equivalent to

javac -classpath MyJar.jar .\GetJar.java

Even you can compile a file from a different directory by passing an absolute file path

javac -classpath MyJar.jar C:\temp\GetJar.java

[Swapnil Suryakant Prabhavalkar]

Hi Ankit,

Thanks.

But in the next example in K&B, they say that specifying (.) in classpath is necessary while giving java command from same directory if .class file is in same directory?

Does javac and java behave differently with this (.) thing?

[Ankit Garg]

javac command requires you to pass it a .java file name which it would compile. If you provide a relative file name then javac will automatically relate it with the current directory as would any other command which requires a file name (for example copy command or del command of windows). java command is different. java command by default looks for classes in the current directory but if you specify the classpath then it will only look for classes in the directories specified in the classpath...

[Swapnil Suryakant Prabhavalkar]

Got it

Thanks a lot, Ankit.

[Kanika Khanna]

In addition to Swapnil's question,I want to know why
javac -classpath MyJar.jar GetJar.java
java -classpath MyJar.jar GetJar.java
is incorrect?

Only one thing is specified in book is current directory i.e. should be super directory of root dirctry i.e myApp.Difference for javac and java is not specified

[ankit rathore]

Go through the following links. It helps me to to get OCJP Certified.

SCJP 6(OCJP) Mock

scjp(OCJP)5 Mock
Core Java
Java EE 5 Business Component Developer Certified Professional Upgrade