Using an ArrayList as Parameter of Constructor

Question

I'm trying to write a constructor for a class which accepts an ArrayList (containing integers) as one of it's arguments. When instantiating this class later, I will pass an appropriate, pre-populated list of values, so I don't want to create an empty list inside the constructor.

Unfortunately, when I try to compile the below code, Java spits out five errors, all related to line 23 (my constructor's function definition). Any advice would be appreciated:

/*
 * SumGenerator
 * 
 * @author James Scholes
*/

import java.util.ArrayList;
import java.util.Random;

public class SumGenerator
{
    // Some initial variables
    public int timesTable;
    public int multiple;

    /*
     * Constructor
     * 
     * @param timesTable(int): The times table to use for sum generation
     * @param limit(int): The highest multiple to use in sum generation
     * @param previousMultiples(ArrayList<Integer>): The previously used multiples to avoid sum duplication
    */
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
    {
        this.timesTable = timesTable;
        Random randomGenerator = new Random();

        // Create a list to store our multiples
        ArrayList<Integer> multiples = new ArrayList<Integer>();
        // and add our multiples to it, only if 
        // they haven't been used before
        for(int i = timesTable; i <= limit; i++)
        {
            if(previousMultiples.contains(i))
            {
                continue;
            }
            else
            {
                multiples.add(i);
            }
        }

        this.multiple = multiples.get(randomGenerator.nextInt(multiples.size()));
    }

}

SumGenerator.java:23: error: ')' expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                 ^
SumGenerator.java:23: error: illegal start of type
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                    ^
SumGenerator.java:23: error: <identifier> expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                      ^
SumGenerator.java:23: error: ';' expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                       ^
SumGenerator.java:23: error: <identifier> expected
    public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)
                                                                                            ^
5 errors

http://stackoverflow.com/questions/997482/does-java-support-default-parameter-values — Paul Grime, Apr 23 '13 at 20:18

score 7 · Answer 1 · answered Apr 23 '13 at 20:16

7

Java doesn't support default arguments.

answered Apr 23 '13 at 20:16

djechlin

59,258
35
162
290

score 6 · Accepted Answer · answered Apr 23 '13 at 20:17

You can't supply default values for parameters in Java: int limit = 10. To work around, supply overloaded constructors. One doesn't have limit and will supply the other with the default value.

public SumGenerator(int timesTable, ArrayList<Integer> previousMultiples)
{
    this(timesTable, 10, previousMultiples);
}

public SumGenerator(int timesTable, int limit, ArrayList<Integer> previousMultiples)
{
    // Your constructor here.
}

score 2 · Answer 3 · answered Apr 23 '13 at 20:17

2

public SumGenerator(int timesTable, int limit = 10, ArrayList<Integer> previousMultiples)

Remove the = 10 in int limit = 10. Java does not support default values for constructor or method arguments.

answered Apr 23 '13 at 20:17

Jesper

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46
318
350

Using an ArrayList as Parameter of Constructor

3 Answers3