Is it possible to get next element in the Stream?

Question

I am trying to converting a for loop to functional code. I need to look ahead one value and also look behind one value. Is it possible using streams? The following code is

Answer 1

Not exactly a Java solution, but possible to get next element in Kotlin with zip functions. Here is what I came up with functions. Looks much cleaner

enum class RomanNumeral(private val value: Int) {
    I(1), V(5), X(10), L(50), C(100), D(500), M(1000);

    operator fun minus(other: RomanNumeral): Int = value - other.value

    operator fun plus(num: Int): Int = num + value

    companion object {
        fun toRoman(ch: Char): RomanNumeral = valueOf(ch.toString())
    }
}

fun toNumber(roman: String): Int {
    return roman.map { RomanNumeral.toRoman(it) }
        .zipWithNext()
        .foldIndexed(0) { i, currentVal, (num1, num2) ->
            when {
                num1 < num2            -> num2 - num1 + currentVal
                i == roman.length - 2  -> num1 + (num2 + currentVal)
                else                   -> num1 + currentVal
            }
        }
}