How can I use List

Question

In fact, I want to use "normOfVector()" method with Integer, and Float, but I couldn't

I get this error:

The method normOfVector(ArrayList) in the type TestMethod is not applicable for the arguments (ArrayList)

    package code;

import java.util.ArrayList;
import java.util.List;

public class TestMethod
{

    public static float normOfVector(ArrayList<Integer> list)
    {
        float sum = 0.0f;
        for (Integer i : list)
            sum = sum + (float) (i * i);
        // end for

        return (float) Math.sqrt(sum);
    }// end function


    public static void main(String[] args)
    {

        // In this case no Problem
        ArrayList<Integer> listI = new ArrayList<>();
        listI.add(0);
        listI.add(3);
        listI.add(5);
        listI.add(7);
        listI.add(2);
        float result = normOfVector(listI);

        // In this case will not work
        ArrayList<Float> listF = new ArrayList<>();
        listF.add(0.0f);
        listF.add(3.0f);
        listF.add(5.0f);
        listF.add(7.0f);
        listF.add(2.0f);
        result = normOfVector(listF);

    }// end main

}// end class

My point is:

I want to create a method that accept the two cases.

Thank you.

Can you please post an [MCVE](http://stackoverflow.com/help/mcve) that we can actually run? — Kevin Workman, Feb 25 '15 at 15:57
I would use `List` as every possible `int` and `float` will fit into a `double` without loss of precision. — Peter Lawrey, Feb 25 '15 at 16:17

score 2 · Accepted Answer · edited May 23 '17 at 11:43

In your first block your are computing numbers but storing them as objects. You should be storing them as Integer or Float, or maybe Double or Number, but not Object. Second in your cos(...) method you should limit what kind of parameters are accepted by changing the declaration to List<Integer>, List<Float> or List<? extends Number>. It may help to study up on java generics and especially using the PECS principle.

Peter Lawrey · Answer 2 · 2015-02-26T14:32:53.343

Based on your updated code.

public class TestMethod {

    public static double normOfVector(List<? extends Number> list) {
        double sum = 0.0;
        for (Number d : list)
            sum += d.doubleValue() * d.doubleValue();

        return Math.sqrt(sum);
    }    

    public static void main(String[] args) {
        List<Integer> listI = new ArrayList<>();
        listI.add(0);
        listI.add(3);
        listI.add(5);
        listI.add(7);
        listI.add(2);
        double result = normOfVector(listI);

        List<Float> listF = new ArrayList<>();
        listF.add(0.0f);
        listF.add(3.0f);
        listF.add(5.0f);
        listF.add(7.0f);
        listF.add(2.0f);
        result = normOfVector(listF);
    }
}

This is how I would write it using List<Double>

Map<String, Double> currentWord = new HashMap<>();
double first = main.getWords().get(firstWord);
for(Map.Entry<String, Double> entry : main.getWords()) {
    String secondWord = entry.getValue();
    double cosValue = vectors.cos(first, entry.getValue());
    if (cosValue >= percentage) {
        currentWord.put(secondWord, Math.round(cosValue * 100) / 100.0);
        break; // is there any point searching for another word?
    }
}

thank you for this idea. I tried to avoid hash map for another reasons that related to another part of my code. — محمد التويجري, Feb 26 '15 at 14:07
@محمدالتويجري why do you have to use `Integer` and `Float` but not `Double`? — Peter Lawrey, Feb 26 '15 at 14:33

score 0 · Answer 3 · answered Mar 26 '18 at 06:52

0

Maybe you can also use something like this:

Number[] numbers = new Number[] { valueOfFloat, valueOfInteger };

answered Mar 26 '18 at 06:52

davidddp

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3 Answers3