compatibility null pointer error?

Question

int e=0;
int Compatibility=0;
int numOfDisagreements=0;
int tsize=likes.size()+dislikes.size();
int numOfCommonLikes=0;
int numOfCommonDislikes=0;
while(e<tsize){
    if (user.likes.get(e).equals(Stranger.likes.get(e))){
        if ((Stranger.howDoYouLike(likes.get(e)))== 1 && user.howDoYouLike(likes.get(e))==1)
        {
            numOfCommonLikes=numOfCommonLikes+1;
        }
    }
    else if (user.dislikes.get(e).equals(Stranger.dislikes.get(e))){
        if ((Stranger.howDoYouLike(dislikes.get(e)))== -1 && user.howDoYouLike(likes.get(e))==-1)
        {
            numOfCommonDislikes=numOfCommonDislikes+1;
        }

Am getting a nullpointer error, I don't know what that means but can someone tell me what is wrong with this code please, I am looking real hard

    else 
    {
        numOfDisagreements=numOfDisagreements+1;
    }

        e+;
    }

    Compatibility=(numOfCommonLikes+ numOfCommonDislikes)- numOfDisagreements;
    return Compatibility;
}

Post (add to your question) exception description and full stack trace. — PM 77-1, Feb 23 '15 at 02:19

score 0 · Answer 1 · answered Feb 23 '15 at 02:36

0

Are you initializing you Lists? I see the line:

int tsize=likes.size()+dislikes.size();

But no proof that you ever created any list objects. A NullPointerException is when you try to use an object that has not yet been created. For example, if I tried to do this:

List<Object> objects;
objects.size();

Then I would get a NullPointerException. I would need to create the list like so:

List<Object> objects;
objects = new List<Object>();

Before I tried to call any method belonging to it.

answered Feb 23 '15 at 02:36

Anonymous Person

307
2
10

ok but now am getting a java.lang.stackoverflowerror: null error – deedee Feb 23 '15 at 02:46
Hmm. I'm not sure. Can you post all of your code so I could see if there is anything else I have missed? – Anonymous Person Feb 23 '15 at 03:19
public class Person { String lastName="";//stores lastname String firstName="";//stores firstname char sex;//stores sex Preference a,d,t;//instances of the Preference enum private ArrayList dislikes = new ArrayList();//dislikes arraylist of type preference private ArrayList likes = new ArrayList();//likes arraylist of type preference Person User;//person object called user – deedee Feb 23 '15 at 04:30
The Person variable you called "user" is never initialized. You never say "user = new Person()" and that is why you get a NullPointerException. The guys who commented on your question were asking you to describe the error message you got. – Anonymous Person Feb 23 '15 at 23:35
am gonna email you something right now and tell me if i am on the right path – deedee Feb 23 '15 at 23:44
You don't need iterators. You can loop through using a foreach loop. This: for (Preference p : likes) / if (Stranger.dislikes.contains(p)) / // do stuff – Anonymous Person Feb 24 '15 at 00:14
Ignore the forward slashes I put in the post. I tried to prevent the words from wrapping oddly. – Anonymous Person Feb 24 '15 at 00:14
getting a 'cannot find symbol class Preference' error here private Preference a,d,t; – deedee Feb 24 '15 at 00:34
What line do you get this on? – Anonymous Person Feb 24 '15 at 00:34
line 11 in the code i sent you........private Preference a,d,t; – deedee Feb 24 '15 at 00:37
Those don't serve any purpose. In the method howDoYouLike(Preference Y), you can just use Y instead of assigning it to t. Although I might be wrong. Please tell me if I am. – Anonymous Person Feb 24 '15 at 00:45
am still getting the same error – deedee Feb 24 '15 at 00:51
There is no way you are getting the same error on the same line if you deleted that line. – Anonymous Person Feb 24 '15 at 00:55
What line do you get the error on? – Anonymous Person Feb 24 '15 at 01:03
the same line as before – deedee Feb 24 '15 at 01:05
I do not know what bluej is. – Anonymous Person Feb 24 '15 at 01:58
Can you resend me the source? Maybe you changed something I'm not aware of. – Anonymous Person Feb 24 '15 at 01:59

compatibility null pointer error?

1 Answers1