I need to convert an int variable to double
JavaJava Problem Overview
My friend is trying to make some kind of calculation as a task for class, and he's having some trouble... I hope you can help him.
The problem is that he gets an input from the user as int (it has to be, it's a part of the task). He is trying to convert it to double in the code below, but this doesn't work. The results are int anyway.
double firstSolution = ((b1 * a22 - b2 * a12) / (a11 * a22 - a12 * a21));
double secondSolution = ((b2 * a11 - b1 * a21) / (a11 * a22 - a12 * a21));
If you need more explanation, I'll ask him for it. Thanks in advance!
Java Solutions
Solution 1 - Java
You have to cast one (or both) of the arguments to the division operator to double
:
double firstSolution = (b1 * a22 - b2 * a12) / (double)(a11 * a22 - a12 * a21);
Since you are performing the same calculation twice I'd recommend refactoring your code:
double determinant = a11 * a22 - a12 * a21;
double firstSolution = (b1 * a22 - b2 * a12) / determinant;
double secondSolution = (b2 * a11 - b1 * a21) / determinant;
This works in the same way, but now there is an implicit cast to double. This conversion from int
to double
is an example of a widening primitive conversion.
Solution 2 - Java
Converting to double can be done by [casting][1] an int to a double:
You can convert an int to a double by using this mechnism like so:
int i = 3; // i is 3
double d = (double) i; // d = 3.0
Alternative (using Java's automatic type recognition):
double d = 1.0 * i; // d = 3.0
Implementing this in your code would be something like:
double firstSolution = ((double)(b1 * a22 - b2 * a12) / (double)(a11 * a22 - a12 * a21));
double secondSolution = ((double)(b2 * a11 - b1 * a21) / (double)(a11 * a22 - a12 * a21));
Alternatively you can use a hard-parameter of type double (1.0) to have java to the work for you, like so:
double firstSolution = ((1.0 * (b1 * a22 - b2 * a12)) / (1.0 * (a11 * a22 - a12 * a21)));
double secondSolution = ((1.0 * (b2 * a11 - b1 * a21)) / (1.0 * (a11 * a22 - a12 * a21)));
Good luck. [1]: https://stackoverflow.com/questions/5289393/casting-variables-in-java
Solution 3 - Java
I think you should casting variable or use Integer
class by call out method doubleValue()
.
Solution 4 - Java
Either use casting as others have already said, or multiply one of the int variables by 1.0
:
double firstSolution = ((1.0* b1 * a22 - b2 * a12) / (a11 * a22 - a12 * a21));