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While I was writing java programs with abstract class, I met below
compilation problems. Hope someone can help.

Case 1
======

File: c:\javapgm\aclass2\aclass1\Aclass1.java

package aclass1;
public abstract class Aclass1 {
private double price;
private String model;
public abstract void goFast();
public abstract void goUpHill();
}

Aclass1.java compiled successfully.

File: c:\javapgm\aclass2\Aclass2.java

import aclass1.Aclass1;

public abstract class Aclass2 extends Aclass1 {
public abstract void goDownHill();
public void goSlow() {
System.out.println ("This is non-abstract method goSlow()");
}
}

Aclass2.java compiled successfully.

File: c:\javapgm\Aclass3.java

import aclass2.Aclass2;

public class Aclass3 extends Aclass2 {
public void goFast() {
System.out.println ("This is non-abstract method goFast()");
}
public void goUpHill() {
System.out.println ("This is non-abstract method goUpHill()");
}
public void goDownHill() {
System.out.println ("This is non-abstract method goDownHill()");
}
}

Compiling Aclass3.java returned below error.

Aclass3.java:1: Cannot access aclass2.Aclass2
bad class file: .\aclass2\Aclass2.class
class file contains wrong class: Aclass2
Please remove or make sure it appears in the correct subdirectory of
the classpath.
import aclass2.Aclass2
^
1 error

Similar problem happened for below class definitions

Case 2
======

File: c:\javapgm\aclass2\aclass1\Aclass1.java

package aclass1;
public abstract class Aclass1 {
private double price;
private String model;
public abstract void goFast();
public abstract void goUpHill();
}

Aclass1.java compiled successfully.

File: c:\javapgm\aclass2\Aclass4.java

import aclass1.Aclass1;

public class Aclass4 extends Aclass1 {
public void goFast() {
System.out.println ("This is non-abstract method goFast()");
}
public void goUpHill() {
System.out.println ("This is non-abstract method goUpHill()");
}
public void goSlow() {
System.out.println ("This is non-abstract method goSlow()");
}
}


Aclass4.java compiled successfully.

File: c:\javapgm\Aclass5.java

import aclass2.Aclass4;

public class Aclass5 extends Aclass4 {
// public void doMore () {
// System.out.println("Calling Aclass4.goFast() inside
Aclass5.doMore()");
// goFast();
// }
public staic void main (String[] args) {
//doMore();
}
}

Compiling Aclass5.java returned below error

Aclass5.java:10: <identifier> expected
public static void main (String[] args) {
^
Aclass5.java:12: ';' expected
}
^
Aclass5.java:3: cannot access aclass2.Aclass4
bad class file: .\aclass2\Aclass4.class
class file contains wrong class: Aclass4
Please remove or make sure it appears in the correct subdirectory of
the classpath.
import aclass2.Aclass4;
^
3 errors

"lonelyplanet999" <> wrote in message
news: om...
> File: c:\javapgm\aclass2\Aclass2.java
>
> import aclass1.Aclass1;
>
> public abstract class Aclass2 extends Aclass1 {
> public abstract void goDownHill();
> public void goSlow() {
> System.out.println ("This is non-abstract method goSlow()");
> }
> }

Is this class in a package, eg
package aclass2;

Peter

"Peter Kirk" <peter_kirk@PLEASE_DONT_SPAM_ME_ANYMORE_alpha-gruppen.NO_MORE_dk_ARGGGGH> wrote in message news:<3f8e474c$0$54856$. dk>...
> "lonelyplanet999" <> wrote in message
> news: om...
> > File: c:\javapgm\aclass2\Aclass2.java
> >
> > import aclass1.Aclass1;
> >
> > public abstract class Aclass2 extends Aclass1 {
> > public abstract void goDownHill();
> > public void goSlow() {
> > System.out.println ("This is non-abstract method goSlow()");
> > }
> > }
>
> Is this class in a package, eg
> package aclass2;

Yes, I missed the package statement. I modified the packages as below:

c:\javapgm\aclass2\aclass1\Aclass1.java

package aclass1;
public abstract class Aclass1 {
private double price;
private String model;
public abstract void goFast();
public abstract void goUpHill();
}

c:\javapgm\aclass2\Aclass2.java

package aclass2;
import aclass1.Aclass1;

public abstract class Aclass2 extends Aclass1 {
public abstract void goDownHill();
public void goSlow() {
System.out.println ("This is non-abstract method goSlow()");
}
}

c:\javapgm\Aclass3.java

package aclass3;
import aclass2.Aclass2;
import aclass2.aclass1.Aclass1;

public class Aclass3 extends Aclass2 {
public void goFast() {
System.out.println ("This is non-abstract method goFast()");
}
public void goUpHill() {
System.out.println ("This is non-abstract method goUpHill()");
}
public void goDownHill() {
System.out.println ("This is non-abstract method goDownHill()");
}
}

Compilation of Aclass1, & Aclass2 packages succeeded but Aclass3
failed with below error.

Aclass3.java:3: cannot access aclass2.aclass1.Aclass1
bad class file: .\aclass2\aclass1\Aclass1.class
class file contains wrong class: aclass1.Aclass1
Please remove or make sure it appears in the correct subdirectory of
the classpath.
import aclass2.aclass1.Aclass1;
^
1 error

If 'import aclass2.aclass1.Aclass1;' statement in Aclass3.java
commented out, below error reported.

Aclass3.java:5: cannot access aclass1.Aclass1
file aclass1\Aclass1.class not found
public class Aclass3 extends Aclass2 {
^
1 error

>
> Peter

"lonelyplanet999" <> wrote in message
news: om...
> Yes, I missed the package statement. I modified the packages as below:
>
> c:\javapgm\aclass2\aclass1\Aclass1.java

<snip>

Hmm. I think you seem to be swapping things around a bit each time. You have
to make sure that the java classes are in the same directory as the pacakage
statement indicates.

Eg. if I have a directory/file like this (where the source files are stored
in a tree under the "src" directory):

c:\myproject\src\a\b\c\MyClass.java

then the package statement in MyClass.java should look like this:

package a.b.c;

Likewise, if I have this file:

c:\myproject\src\d\e\f\MyOtherClass.java

then the package statement in MyOtherClass.java should look like this:

package d.e.f;

Then, if MyOtherClass should extend MyClass (or just use it in some way),
then I need an import statement in MyOtherClass, like this:

import a.b.c.MyClass;


Hope you can make some sense of that, and get your classes to compile.

Peter

"Peter Kirk" <peter_kirk@PLEASE_DONT_SPAM_ME_ANYMORE_alpha-gruppen.NO_MORE_dk_ARGGGGH> wrote in message news:<3f8f9b23$0$54835$. dk>...
> "lonelyplanet999" <> wrote in message
> news: om...
> > Yes, I missed the package statement. I modified the packages as below:
> >
> > c:\javapgm\aclass2\aclass1\Aclass1.java
>
> <snip>
>
> Hmm. I think you seem to be swapping things around a bit each time. You have
> to make sure that the java classes are in the same directory as the pacakage
> statement indicates.
>
> Eg. if I have a directory/file like this (where the source files are stored
> in a tree under the "src" directory):
>
> c:\myproject\src\a\b\c\MyClass.java

If I don't interpret wrongly, I also follow the rule.

The only difference is the classes defined recursively extends another
one, as described below:

c:\myproject\src\Aclass3.java has only one non-abstract class named
Aclass3. This class extends another class Aclass2.

c:\myproject\src\aclass2\Aclass2.java has only one abstract class
named Aclass2. This class extends another class Aclass1.

c:\myproject\src\aclass2\aclass1\Aclass1.java has only one abstract
class named Aclass1. This class doesn't extend any other class.

The first statement inside Aclass1.java is
package aclass1;

The first 2 statements inside Aclass2.java are
package aclass2;
import aclass1.Aclass1;

The first 3 statements inside Aclass3.java are
package aclass3;
import aclass2.Aclass2;
import aclass2.aclass1.Aclass1;

Compilation of Aclass1.java & Aclass2.java succeeded but that of
Aclass3.java failed. Even if I commented statement 'import
aclass2.aclass1.Aclass1;', compilation still failed.

What I don't understand is what java rule I have violated that caused
the compilation failure.

>
> then the package statement in MyClass.java should look like this:
>
> package a.b.c;
>
> Likewise, if I have this file:
>
> c:\myproject\src\d\e\f\MyOtherClass.java
>
> then the package statement in MyOtherClass.java should look like this:
>
> package d.e.f;
>
> Then, if MyOtherClass should extend MyClass (or just use it in some way),
> then I need an import statement in MyOtherClass, like this:
>
> import a.b.c.MyClass;
>
>
> Hope you can make some sense of that, and get your classes to compile.
>
> Peter

"lonelyplanet999" <> wrote in message
news: om...

<snip>

> c:\myproject\src\aclass2\aclass1\Aclass1.java has only one abstract
> class named Aclass1. This class doesn't extend any other class.
>
> The first statement inside Aclass1.java is
> package aclass1;

But isn't this wrong? You have Aclass1.java in directory \aclass2\aclass1\
yet the package statement says just aclass1.


> The first 2 statements inside Aclass2.java are
> package aclass2;
> import aclass1.Aclass1;

Here you are saying that Aclass1 is in package aclass1....

> The first 3 statements inside Aclass3.java are
> package aclass3;
> import aclass2.Aclass2;
> import aclass2.aclass1.Aclass1;

.....and here you are saying that Aclass1 is in package aclass2.aclass1


> Compilation of Aclass1.java & Aclass2.java succeeded but that of
> Aclass3.java failed. Even if I commented statement 'import
> aclass2.aclass1.Aclass1;', compilation still failed.

I'm surprised that any of them compiled. As far as I can see Aclass1 should
not have compiled because its package statement does not match the directory
in which it lies. This would mean that Aclass2 cannot compile - because it
tries to use the non-existent Aclass1. Likewise for Aclass3.

"Peter Kirk" <peter_kirk@PLEASE_DONT_SPAM_ME_ANYMORE_alpha-gruppen.NO_MORE_dk_ARGGGGH> wrote in message news:<3f92a23f$0$54862$. dk>...
> "lonelyplanet999" <> wrote in message
> news: om...
>
> <snip>
>
> > c:\myproject\src\aclass2\aclass1\Aclass1.java has only one abstract
> > class named Aclass1. This class doesn't extend any other class.
> >
> > The first statement inside Aclass1.java is
> > package aclass1;
>
> But isn't this wrong? You have Aclass1.java in directory \aclass2\aclass1\
> yet the package statement says just aclass1.
>
>
> > The first 2 statements inside Aclass2.java are
> > package aclass2;
> > import aclass1.Aclass1;
>
> Here you are saying that Aclass1 is in package aclass1....
>
> > The first 3 statements inside Aclass3.java are
> > package aclass3;
> > import aclass2.Aclass2;
> > import aclass2.aclass1.Aclass1;
>
> ....and here you are saying that Aclass1 is in package aclass2.aclass1
>
>
> > Compilation of Aclass1.java & Aclass2.java succeeded but that of
> > Aclass3.java failed. Even if I commented statement 'import
> > aclass2.aclass1.Aclass1;', compilation still failed.
>
> I'm surprised that any of them compiled. As far as I can see Aclass1 should

Last time I 'cd c:\myproject\src\aclass2\aclass1\' then run
c:\j2sdk1.4.1_01\bin\javac Aclass1.java. The compilation really
returned no error.

Then I 'cd c:\myproject\src\aclass2\', then run
c:\j2sdk1.4.1_01\bin\javac Aclass2.java. The compilation really
returned no error, too.

Compilation failed only when I run javac Aclass3.java after I 'cd
c:\myproject\src\'

> not have compiled because its package statement does not match the directory
> in which it lies. This would mean that Aclass2 cannot compile - because it
> tries to use the non-existent Aclass1. Likewise for Aclass3.

As you suggested, now I changed the package declaration statements as
below:

In c:\myproject\src\aclass2\aclass1\Aclass1.java I wrote
package aclass2.aclass1;

In c:\myproject\src\aclass2\Aclass2.java I wrote
package aclass2;
import aclass2.aclass1.Aclass1;

In c:\myproject\src\Aclass3.java I wrote
package aclass3;
import aclass2.Aclass2;
import aclass2.aclass1.Aclass1;

Then I called javac at directory c:\myproject\src for all the 3 .java
files i.e.

\j2sdk1.4.1_01\bin\javac aclass2\aclass1\Aclass1.java
\j2sdk1.4.1_01\bin\javac aclass2\Aclass2.java
\j2sdk1.4.1_01\bin\javac Aclass3.java

All compilation succeeded then. Also, all Aclass?.java corresponding
..class files were put into their respective directories along with
their associated .java filed.

I would like to ask if Aclass3.java is not under the same directory
root as Aclass2.java & Aclass1.java, say Aclass3.java under
c:\myproject\, Aclass2.java & Aclass1.java under c:\classes\ &
c:\classes\aclass1, will java allows that ?