Java ArrayList<Double> as Parameter

Question

I am currently working on a lab and would like to know how to handle the following problem which I have spent at least two hours on:

I am asked to create an ArrayList containing the values 1, 2, 3, 4 and 10. Whilst I usually never have any trouble creating an ArrayList with said values, I am having trouble this time. Should I create the ArrayList outside of the method or inside the method? Whichever way I have attempted it, I have been presented with numerous error messages. How do I add values to this ArrayList parameter? I have attempted to add values to it when calling it from the main method, but this still doesn't work. Here is the method in question.

public static double ScalesFitness(ArrayList<Double> weights){
    //code emitted for illustration purposes
}

If anybody could help me it would be greatly appreciated. If any more code is required, then please let me know.

Thank you so much.

Mick.

EDIT: The code for the class in question is as follows:

import java.util.*;

public class ScalesSolution
{
private static String scasol;
//Creates a new scales solution based on a string parameter
//The string parameter is checked to see if it contains all zeros and ones
//Otherwise the random binary string generator is used (n = length of parameter)
public ScalesSolution(String s)
{
    boolean ok = true;
    int n = s.length();
    for(int i=0;i<n;++i)
    {
        char si = s.charAt(i);
        if (si != '0' && si != '1') ok = false;
    }
    if (ok)
    {
        scasol = s;
    }
    else
    {
        scasol = RandomBinaryString(n);
    }
}
private static String RandomBinaryString(int n)
{
    String s = new String();

    for(int i = 0; i > s.length(); i++){
        CS2004.UI(0,1);
            if(i == 0){
                System.out.println(s + "0");
            }
            else if(i == 0){
                System.out.println(s + "1");
            }
    }

    return(s);
}
public ScalesSolution(int n) 
{
    scasol = RandomBinaryString(n); 
}
//This is the fitness function for the Scales problem
//This function returns -1 if the number of weights is less than
//the size of the current solution



public static double scalesFitness(ArrayList<Double> weights)
{   
    if (scasol.length() > weights.size()) return(-1);
    double lhs = 0.0,rhs = 0.0;

    double L = 0;
    double R = 0;

    for(int i = 0; i < scasol.length(); i++){
        if(lhs == 0){
            L = L + i;
        }
        else{
            R = R + i;
        }
    }

    int n = scasol.length();

    return(Math.abs(lhs-rhs));
}
//Display the string without a new line
public void print()
{
    System.out.print(scasol);
}
//Display the string with a new line
public void println()
{
    print();
    System.out.println();
}

}

The other class file that I am using (Lab7) is:

import java.util.ArrayList;

public class Lab7 {

public static void main(String args[])
{

    for(int i = 0 ; i < 10; ++i)
    {
        double x = CS2004.UI(-1, 1);
        System.out.println(x);
    }

    System.out.println();

    ScalesSolution s = new ScalesSolution("10101");
    s.println();

}

}

Define "Doesn't work"? Perhaps some code and error messages? The snippit above is fine. — Brian Roach
– Brian Roach, Commented Mar 14, 2011 at 1:40
Hi Brian. If I attempt to add the following outside of the method: ArrayList<Double> weights = {1, 2, 3, 4, 10}; then I am presented with the following error message: Type mismatch: cannot convert from int[] to ArrayList<Double>. I am then prompted to change the type of array to int[] which is not what I am looking to do. If I add the same statement within the method, I am prompted to rename 'weights' and, once again, to change the type of array to int[]. I hope this helps? — Mus
– Mus, Commented Mar 14, 2011 at 1:45
the answers below from others should now help. When you say {1, 2, 3, 4, 10} it's an implicit array of int (int[]), which you can't give to ArrayList<Double>. If you don't need the features of the ArrayList, you could also just use double[] myWeights = { 1.0, 2.0, 3.0, 4.0, 10.0 } and have your method take double[] weights — Brian Roach
– Brian Roach, Commented Mar 14, 2011 at 3:18

joel1di1 · Accepted Answer · 2011-03-14 02:04:01Z

2

you can these

1) use varargs instead of list

public static double scalesFitness(Double...weights)

so you can call this method with :

scalesFitness(1.0, 2.0, 3.0, 4.0, 10.0);

2) create the list outside your method

ArrayList<Double> weights = new ArrayList<Double>();
weights.add(1.0); 
weights.add(2.0); 
weights.add(3.0); 
weights.add(4.0); 
weights.add(10.0); 

scalesFitness(weights);

edited Mar 14, 2011 at 2:04

answered Mar 14, 2011 at 1:57

joel1di1

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2 Comments

Mark Peters Over a year ago

new ArrayList<Double>(Arrays.asList(1.0, 2.0, ...)) works too. Though ideally the method wouldn't require an ArrayList but rather a List so you could just use Arrays.asList(1.0, 2.0, ...).

joel1di1 Over a year ago

I agree with the use of List : scalesFitness(List<Double> weights)

user unknown · Accepted Answer · 2011-03-14 02:45:32Z

1

Towards your initial posting, this would work:

scalesFitness (new ArrayList<Double> (Arrays.asList (new Double [] {1.0, 2.0, 4.0, 10.0})));

You may explicitly list the values in Array form, but

you have to use 1.0 instead of 1, to indicate doubles
you have to prefix it with new Double [] to make an Array, and an Array not just of doubles
Arrays.asList() creates a form of List, but not an ArrayList, but
fortunately, ArrayList accepts a Collection as initial parameter in its constructor.

So with nearly no boilerplate, you're done. :)

If you can rewrite scalesFitness that would be of course a bit more easy. List<Double> as parameter is already an improvement.

answered Mar 14, 2011 at 2:45

user unknown

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Comments

camickr · Accepted Answer · 2011-03-14 01:39:53Z

0

Should I create the ArrayList outside of the method or inside the method?

The ArrayList is a parameter for the method so it need to be created outside the method, before you invoke the method.

answered Mar 14, 2011 at 1:39

camickr

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2 Comments

Mus Over a year ago

Thank you, but whenever I try this, I am prompted to change the type of 'weights' to 'int[]' which I am not looking to do...may I ask how you would suggest to do this?

Brian Roach Over a year ago

@Mick - we'd need code. That would indicate you're not understanding what you're creating and passing.

Evan Ross Davis · Accepted Answer · 2018-07-01 20:33:00Z

0

You need to import ArrayList in the file that includes your methods. This is probably solved but that's the issue I was encountering.

answered Jul 1, 2018 at 20:33

Evan Ross Davis

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