This is the problem
double a = null;
NullPointerException will arise every time you use it until you initialize it. So this:
a[i] = var;
A possible solution would be initialize it when declaring it:
double a = new double[PUT_A_LENGTH_HERE]; //seems like this constant should be 7
IMO more important than solving this exception, is the fact that you should learn to read the stacktrace and understand what it says, so you could detect the problems and solve it.
This exception means there’s a variable with
null value being used. How to solve? Just make sure the variable is not
null before being used.
This line has two parts:
- First, shows the class and method where the error was thrown. In this case, it was at
<init>method in class
TwoTenBdeclared in package
twoten. When you encounter an error message with
SomeClassName.<init>, means the error was thrown while creating a new instance of the class e.g. executing the constructor (in this case that seems to be the problem).
- Secondly, shows the file and line number location where the error is thrown, which is between parenthesis. This way is easier to spot where the error arose. So you have to look into file TwoTenB.java, line number 29. This seems to be
a[i] = var;.
From this line, other lines will be similar to tell you where the error arose. So when reading this:
It means that you were trying to instantiate a
TwoTenB object reference inside the
main method of your class
JavaPractice declared in