Android Studio “从未使用过变量”，但实际使用过（BigInteger 问题，未解决的参考资料）

Question

So, good day eveyone.

I'm starting to write my very first own app with kotlin via Android Studio, and I have one problem that I cannot solve. When writing down this code: (bi is used infront of every variable that is a BigInteger btw.)

if (length == 2) {
     val bicombinations: BigInteger = valueOf(bivariations.toLong())
           .multiply(bivariations)
    }

it tells me, that "bicombinations" is never used. However, I actually use it in this line here:

val biresult: BigInteger = bicombinations.divide(bipcpower)

At this line, I get another error/warning for bicombinations, "unsolved reference: bicombinations"

EDIT: The second warning now went to: "Variable 'bicombinations' must be initialized." I know how to fix this when using an Int or Double or whatever, but since BigIntegers are vals, I just cannot set a value on bicombinations outside the if statement

EDIT 2: That's how the initialization problem is solved: First, declare bicombinations outside the if branch like so:

var bicombinations: BigInteger = ONE

and inside the if branch, just use bicombinations without the "val" before it, and don't declare it as a BigInteger again. Thanks @Elliot-frisch

Can anyone tell me what to do? This would really help me finishing my app!

Answer 1

Change your code like below (Need to define your variable outside if block)

val bicombinations: BigInteger

if (length == 2) {
 bicombinations = valueOf(bivariations.toLong())
       .multiply(bivariations)
}

Answer 2

Until there is a guarantee of a variable is set, the variable is not in scope (aka in reference), so you may need to set the variable in all the condition before using it outside the if condition.

Either move the result code inside the if branch

if (length == 2) {
    val bicombinations: BigInteger = valueOf(bivariations.toLong())
        .multiply(bivariations)
    val biresult: BigInteger = bicombinations.divide(bipcpower)
}

or add an else branch to if that ensures the variable bicombination is set

val bicombinations: BigInteger
if (length == 2) {
    bicombinations = valueOf(bivariations.toLong())
        .multiply(bivariations)
} else {
    bicombination = BigInteger(0)
}
val biresult: BigInteger = bicombinations.divide(bipcpower)

Answer 3

val biresult=0.toBigInteger()

This way you can initialize biresult. When you define a variable in if statement, you can't use it out of that and you get unresolved reference error. You should define it in your function not to get this error.