sweet swift Return function : wish in Java

import UIKit

import Darwin

func average(nums: Int...) -> Double {

    var sum = 0

    

    for num in nums {

        sum += num

    }

    return Double(sum) / Double (nums.count)

}

func sum(nums: Int...) -> Double {

    var sum = 0

    

    for num in nums {

        sum += num

    }

    return Double(sum)

}

func doMath(mathOp: String)-> (Int...)->Double{

    if mathOp == "average" {

        return average

    }else{

        return sum

    }

}

var mathFunc = doMath(mathOp: "average")

print(mathFunc(1,3,4,5,6,78,67,5,4,4,9))