Addition in Java 8 using BinaryOperator

Question

  package com.operators;

    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import java.util.Scanner;
    import java.util.function.BinaryOperator;

    public class TotalCost {

        public static void main(String[] args) {
            Scanner scan = new Scanner(System.in);
            double mealCost = scan.nextDouble(); // original meal price
            int tipPercent = scan.nextInt(); // tip percentage
            int taxPercent = scan.nextInt(); // tax percentage
            scan.close();

            Map<Double,Double> map = new HashMap<>();
            map.put(mealCost, (double)tipPercent);
            map.put(mealCost, (double)taxPercent);

            BinaryOperator<Double> opPercent = (t1,t2) -> (t1*t2)/100;
            BinaryOperator<Double> opSum = (t1,t2) -> (t1+t2);   
            calculation(opPercent,map);
        }

        public static void calculation(BinaryOperator<Double> opPercent , Map<Double,Double> map) {
            List<Double> biList = new ArrayList<>();
            map.forEach((s1,s2)-> biList.add(opPercent.apply(s1, s2)));
        }
    }

1. I have the below problem which I am trying to solve in Java 8 using BinaryOperator.There are three inputs to this application [mealCost(double), tipPercent(int),taxPercent(int)].

2. I am trying to calculate the below values :

   tip = (mealCost*tipPercent)/100;
   tax = (mealCost*taxPercent)/100;
   TotalCost = mealCost+tip +tax;   
   

3. I am unable to pass an integer input to the apply method of BinaryOperator. Also the calculated value into biList is not proper. Below is my code

Answer 1

You are putting the same key twice in a Map, so the second value overrides the first value. I don't think a Map is appropriate for these calculations. You can use a List<SomePairType> instead.

Or keep mealCost in one variable and the other values in a List<Double>:

    public static void calculation(BinaryOperator<Double> opPercent, Double cost, List<Double> rates) {
        List<Double> biList = new ArrayList<>();
        rates.forEach(d-> biList.add(opPercent.apply(cost, d)));
    }