public class Tabel {
private static int dimension;
private ArrayList<ArrayList<Character>> tabel;
public Tabel(int dimension) {
Tabel.dimension = dimension;
for (int i=0;i<Tabel.dimension*Tabel.dimension;i++) {
tabel.add(new ArrayList<Character>());
}
}
}
When I try to debug (eclipse ide) I get a lot of weird "errors" or at the very least I encounter something I consider unexpected.
The private static int does not appear in the "variables" section of debug.
I get a NullPointerException
on tabel.add(...)
but when I watch the debug, it enters the for
once, does not add anything in the table because when I hit "next" instead of jumping to the closing braces it jumps out of the function.
If I comment the .add
it works so that's the problem (I think). Is my syntax wrong ? or should I post more code ?
tabel
is not initialized, so it is null.
Change
private ArrayList<ArrayList<Character>> tabel;
to
private ArrayList<ArrayList<Character>> tabel = new ArrayList<ArrayList<Character>>();
Or better:
private List<ArrayList<Character>> tabel = new ArrayList<ArrayList<Character>>();
since this does not tie tabel
to ArrayList
.
You have not initialized the private
List. Do the following:
private List<ArrayList<Character>> tabel = new ArrayList<ArrayList<Character>>();
I'd have trouble understanding that level of nesting too.
It's better to refer to List rather than ArrayList. Unless you need a method in the concrete class, it makes your program more flexible to refer to the interface and the methods in the interface.
Create a class (1) that has a field defined as a List of Character. Set the field to a new ArrayList in the constructor.
Create another class (2) that has a field defined as a List of class (1). Set the field to a new ArrayList in the constructor.
Create another class (3) that has a field defined as a List of class (2). Set the field to a new ArrayList in the constructor.
Since you understand what you're doing, you can give these 3 classes more meaningful names.
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