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as4532@drexel.edu - 16 Apr 2006 21:59 GMT

Hi all,
I have a newbie question about extending classes in Java. I have 2
files File1.java and File2.java. File1.java is the base class and
File2.java extends it.

//File2.java

public class File2 extends File1 {
....

}

Both files are in the same folder in my C:\. I get the error saying
Cannot find symbol File1 when i try to compile File2.java. What should
i do here to use an existing class in another java program when both
.java files are present in the same folder.

Thanks
A

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Mark Thomas - 16 Apr 2006 22:49 GMT

> Hi all,
> I have a newbie question about extending classes in Java. I have 2
[quoted text clipped - 15 lines]
> Thanks
> A

Has File1.java compiled cleanly?
Note that these are not separate java programs - just two java classes.
Even calling them Files tends to be misleading.

Mark

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as4532@drexel.edu - 16 Apr 2006 22:54 GMT

Hi Mark,
Yes File1.java compiles. Only File2.java throws an error saying-
"Cannot find the symbol" against File1.

Thanks

> > Hi all,
> > I have a newbie question about extending classes in Java. I have 2
[quoted text clipped - 21 lines]
>
> Mark

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Mark Thomas - 16 Apr 2006 23:26 GMT

> Hi Mark,
> Yes File1.java compiles. Only File2.java throws an error saying-
[quoted text clipped - 27 lines]
>>
>> Mark

Post the full source - there's not enough information here.

Mark

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as4532@drexel.edu - 17 Apr 2006 00:02 GMT

Mark, Here is the source. Customer.java compiles while
CustomerTest.java doesn't. Thanks

//Customer.java

public class Customer{
    private String fname, lname;
    public static void main(String[] args){
    }

    public Customer(String firstname, String lastname){
    this.fname=firstname;
    this.lname=lastname;
    }
}

//CustomerTest.java

public class CustomerTest extends Customer{
    public static void main(String[] args){
    Customer p=new Customer("fname","lname");
    }
}

> > Hi Mark,
> > Yes File1.java compiles. Only File2.java throws an error saying-
[quoted text clipped - 31 lines]
>
> Mark

Reply to this Message

Mark Thomas - 17 Apr 2006 12:06 GMT

> Mark, Here is the source. Customer.java compiles while
> CustomerTest.java doesn't. Thanks
[quoted text clipped - 54 lines]
>>
>> Mark

Ah! You misquoted the error message - it doesn't say "Cannot find
symbol File1 (or Customer)" rather "cannot find symbol : constructor
Customer()". Your CustomerTest class doesn't define a constructor -
when that happens, Java provides you with a default no-argument
constructor. Any constructor always calls the corresponding constructor
in its superclass, in this case that would be a no-argument constructor
in Customer - and you haven't got one! Hence the error message. Note
that as soon as you provide a constructor for a class, as you have for
Customer, you lose the default constructor.

Here the is no reason for CustomerTest to extend Customer. It is not a
subclass (there is no way that a CustomerTest is-a-kind-of Customer),
but a class that uses Customer. So remove the 'extends Customer' and
all will be well.

Always give the actual error message that is causing you problems -
having read it first!

Mark

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as4532@drexel.edu - 17 Apr 2006 12:38 GMT

Thanks for the reply Mark. I removed the word "extends". Now this is
the error message i am getting:

CustomerTest.java:11: cannot find symbol
symbol: class Customer
Location: class CustomerTest

Customer p=new Customer("fname","lname")

What i need to know is that how can i use the class which is in a
different .java file but same directory as my current .java file.

> > Mark, Here is the source. Customer.java compiles while
> > CustomerTest.java doesn't. Thanks
[quoted text clipped - 74 lines]
>
> Mark

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Venkatesh - 17 Apr 2006 14:26 GMT

U need to either set your classpath properly: Include "current
directory" in your classpath by saying
SET CLASSPATH=%CLASSPATH%;. in windows
or
CLASSPATH=$CLASSPATH:. in unix machines

Then run javac

Otherwise, u can compile both java files together, use
javac Customer.java CustomerTest.java

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as4532@drexel.edu - 17 Apr 2006 14:46 GMT

Hi Venkatesh,
Thanks a lot for the help. Classpath was the issue.. when i
compiled the 2 classes together it works fine. Thanks again!

A

> U need to either set your classpath properly: Include "current
> directory" in your classpath by saying
[quoted text clipped - 6 lines]
> Otherwise, u can compile both java files together, use
> javac Customer.java CustomerTest.java

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