i have a 2 data classes
first:
public class Question {
public CharSequence question;
public Answer answers[];
}
second:
public class Answer {
public CharSequence text;
public int number;
}
now i want to save an Answer to Question:
Question qstn.answers = new Answer[2];
[...]
But i got an NullPointerException. Whats wrong? Can't I change the length of an Array in an other class?
Can't I change the length of an Array in an other class?
That is not the problem.
The problem is that you haven't initialized qstn yet.
What you should be doing is:
Question qstn = new Question();
qstn.answers = new Answer[2];
Have you created a new instance of Question first e.g.
Question qstn = new Question();
qstn.answers = new Answer[2];
Also unless you're optimising judiciously, then you'd probably want to give encapsulation a go and make the instance variables private. Access through a public API e.g. getters or/and setters.
Also you may want to instantiate answers when the Object is created e.g.
public class Question {
public CharSequence question;
public Answer answers[] = new Answer[2];
}
Or you could do this in the constructor of Question (you'd need to add a Constructor, as the compiler will be generating you a non-arg Constructor by default with the way things stand).
You need to instantiate your Question class, first:
Question qstn = new Question();
Try this:
Question qstn = new Question();
qstn.answers = new Answer[2];
Yes. You can change the length of arrays in another class.
Please check whether you have initialized the variable qstn.
Question qstn = new Question();
