Hi JKay
You can have an int static (class level member) in the Student class
that keeps the current count. Then a method that returns the next
Integer, to be used in the class constructor. Something like this (it is
not actually how I did, but it is about the same thing):
public class Sudent {
// The Student ID
*private Integer studentID = null;*
// The Student infos
private StudendRecord studentDetails = null;
// The constructor fills in the data about the student
*public Student()*{
// Increment the counter
*this.studentID = Student.nextCounter()*;
// Attach a StudentRecord
this.studentDetail = new StudentRecord();
}
// The static int value keeps the current ID
private static int *currentCounter* = 0;
// The following method increments the counter
private static Integer *nextCounter*(){
return new Integer( currentCounter++ );
}
.... and so on
}
Hope it helps
Mihai
JKay a écrit :
Ok still having problems with this.
First problem - how to get studentId to increment? Can you do studentId
++ for an Integer object? In the end I ended up making studentId a
class variable that is incremented and creating an instance variable
of int type called Id that holds the student's studentId. Otherwise
the studentId was always 3 when printed - might have just been
printing in the wrong order, but shouldn't you be able to assign each
student their own studentId?
Second problem - forgot what it was...
Have submitted the homework now, and it works, but don't feel its as
was intended. Could just be misinterpretation of the instructions on
my part though... For example:
The Student class has studentId instance variable whose type is
Integer type.
-I've made studentId a class variable and a separate instance variable
called Id.
On May 15, 11:05 am, "Nick Dolan" <[email protected]> wrote:
Take studentercord out from settee Anna is the object and you call set on that
e.g
anna.setName("Anna");
Nick
07961171046
-----Original Message-----
From: Mihai DINCA <[email protected]>
Date: Sat, 15 May 2010 11:05:35
To: <[email protected]>
Cc: Java Programming Online Training Course By Sang
Shin<[email protected]>
Subject: Re: [java programming] Re: Homework 1014
I think your constructor for the class Student must do "studentRecord =
new StrudentRecord()" or something like this.
Hope it helps
mihai
JKay a écrit :
Tried to post the entire project here, but moderator said no.
Apparently we're not allowed to post large volumes of code, just small
snippets?
The project is 3 classes (StudentRecordExample.java[MAIN],
StudentRecord.java,Student.java), which have been modified from the
original MyStudentRecordExampleProject so its a bit bulky and could do
with a lot of streamlining, but I figure it should work anyways. As
said the error I'm getting is:
Exception in thread "main" java.lang.NullPointerException
at StudentRecordExample.main(StudentRecordExample.java:35)
Java Result: 1
I used the 'new' keyword to create an instance of a Student object
like so in StudentRecordExample.java:
Student anna = new Student();
Then to set the name variable for object anna of class Student, I
used:
anna.studentRecord.setName("Anna");
which as I understand it gets method setName from class studentRecord.
Do I have to explicitly link classes Student and StudentRecord some
how for this to work? BTW this line of code where I set anna's name
variable is highlighted when I click on the error, and is on line 35.
On May 14, 6:00 pm, Nic Fox <[email protected]> wrote:
Without seeing your code it's hard to say.
So you've used the 'new' keyword to make an instance of a Student
object?
E.g. Student anna = new Student();
And then you use something like:
anna.name = "Anna";
If you've done those things then it could be an issue with variable
scope perhaps?
On 14/05/2010, at 11:47 PM, JKay wrote:
I keep getting the following error when I run my program:
Exception in thread "main" java.lang.NullPointerException
at StudentRecordExample.main(StudentRecordExample.java:35)
I looked up what java.lang.NullPointException is in the API and found
this:
"public class NullPointerException
extends RuntimeException
Thrown when an application attempts to use null in a case where an
object is required. These include:
* Calling the instance method of a null object.
* Accessing or modifying the field of a null object.
* Taking the length of null as if it were an array.
* Accessing or modifying the slots of null as if it were an array.
* Throwing null as if it were a Throwable value.
Applications should throw instances of this class to indicate other
illegal uses of the null object."
Which as far as I understand means that I'm trying to do something
with a null object. Said object is object anna of class Student, and
the method on the line that is throwing the exception is me attempting
to set the name variable for anna to "Anna"
Any ideas?
James
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