Trouble using access functions in an array of objects

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Aki Laukkanen - 31 May 2004 14:14 GMT

Okay, here's what i've got stuck with this time:
I have an array of objects, and I want to set properties of each object
in the array using the objects' access function.
While doing this, i get a NullPointerException.
What am I doing wrong?

Example of the code:

class Member {
    private long aValue;
    public void SetAValue(long aValue){
        this.aValue = aValue;
    }
}
//The following is written in the main function of another class:
Member[] Members = new Member[10];
for(int i = 0; i < 10; i++){
    Members[i].SetAValue(5);
}

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-Aki "Sus" Laukkanen

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Andrew Thompson - 31 May 2004 14:26 GMT

> class Member {
> private long aValue;

This would be better called
private long value;

> public void SetAValue(long aValue){
> this.aValue = aValue;

public void setValue(long value){
this.value = value;

> }
> }
> //The following is written in the main function of another class:
> Member[] Members = new Member[10];
> for(int i = 0; i < 10; i++){

    // instantiate a new 'Member' object..
    Members[i] = new Member();
    // should work now,,
    Members[i].setValue(5);

> }

HTH

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Andrew Thompson
http://www.PhySci.org/ Open-source software suite
http://www.PhySci.org/codes/ Web & IT Help
http://www.1point1C.org/ Science & Technology

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Ryan Stewart - 31 May 2004 14:30 GMT

> Okay, here's what i've got stuck with this time:
> I have an array of objects, and I want to set properties of each object
[quoted text clipped - 15 lines]
> Members[i].SetAValue(5);
> }

You haven't created any Members, just an array to hold them.

Member[] members = new Member[10];
for (int i = 0; i < members.length; i++) {
members[i] = new Member();
members[i].SetAValue(5);
}

Also, variable and method names should start with a lowercase letter.

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Aki Laukkanen - 31 May 2004 14:46 GMT

...

> You haven't created any Members, just an array to hold them.
>
[quoted text clipped - 3 lines]
> members[i].SetAValue(5);
> }

That solved the initial problem (thanks :) , but now I get the error
message "non-static variable this cannot be referenced from a static
context ..."

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-Aki "Sus" Laukkanen

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Andrew Thompson - 31 May 2004 15:09 GMT

> now I get the error
> message "non-static variable this cannot be referenced from a static
> context ..."

The error is not in the snippets you have
mentioned, I suggest a self contained
example of your current code (short!)
<http://www.physci.org/codes/sscce.jsp>

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Andrew Thompson
http://www.PhySci.org/ Open-source software suite
http://www.PhySci.org/codes/ Web & IT Help
http://www.1point1C.org/ Science & Technology

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Aki Laukkanen - 31 May 2004 15:50 GMT

>>now I get the error
>>message "non-static variable this cannot be referenced from a static
[quoted text clipped - 4 lines]
> example of your current code (short!)
> <http://www.physci.org/codes/sscce.jsp>

Figured the 2nd problem out already;
I hadn't made a proper class declaration for the main class. (duh!) %)
Thanks again for helping me out with the first puzzler.

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-Aki "Sus" Laukkanen

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Andrew Thompson - 31 May 2004 15:58 GMT

>> <http://www.physci.org/codes/sscce.jsp>
>>
> Figured the 2nd problem out already;

Cool. Keep the SSCCE in mind
for the next question. ;-)

> I hadn't made a proper class declaration for the main class. (duh!) %)
> Thanks again for helping me out with the first puzzler.

You're welcome.

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Andrew Thompson
http://www.PhySci.org/ Open-source software suite
http://www.PhySci.org/codes/ Web & IT Help
http://www.1point1C.org/ Science & Technology

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Trouble using access functions in an array of objects

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