Can't add to ArrayLists in the constructor

Question

The code in the constructor does not get called. I have to invoke an additional function to call the code.

Test Code:

public static void main(String[] args){
            SourceClass myClass = new SourceClass();
            myClass.Populate();//If this line is removed it does not work
            System.out.println(myClass.GetDescGroup());

        }

Code being tested:

 public class SourceClass {

    static ArrayList<String> line = new ArrayList<String>();
    static ArrayList<ArrayList> description = new ArrayList<ArrayList>();
    static ArrayList<ArrayList> descGroup = new ArrayList<ArrayList>();

    public void SourceClass () {
        //Does not work.
        String testLine = new String("1 v1 v2 v3");
        String[] testLineSplit = testLine.split(" ");
        for (int i = 0; i < testLineSplit.length;i++) {
            line.add(testLineSplit[i]);
        }

        description.add(line);
        descGroup.add(description);     
    }

    public void Populate() {
        //works
        String testLine = new String("1 v1 v2 v3");
        String[] testLineSplit = testLine.split(" ");
        for (int i = 0; i < testLineSplit.length;i++) {
            line.add(testLineSplit[i]);
        }

        description.add(line);
        descGroup.add(description);
    }

    public String GetDescGroup() {
        return descGroup.get(0).get(0).toString();
    }
}

Same code goes in Populate() and SourceClass()

When a function is called to get the ArrayList it just turns up as empty

Show us complete code.. Where is it working? where is it not working? — TheLostMind
– TheLostMind, Commented May 7, 2015 at 10:39

Veselin Davidov · Accepted Answer · 2015-05-07 10:56:20Z

2

Your method SourceClass has a return type void which makes it a method and not a constructor. So when you create an object with new SourceClass it calls the default empty constructor

The constructor must be :

public SourceClass () {
 ....
}

answered May 7, 2015 at 10:56

Veselin Davidov

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Comments

forgivenson · Accepted Answer · 2015-05-07 11:08:57Z

0

When you define a constructor, don't give it a return value.

In you code:

public void SourceClass () {
    //Does not work.
    String testLine = new String("1 v1 v2 v3");
    String[] testLineSplit = testLine.split(" ");
    for (int i = 0; i < testLineSplit.length;i++) {
        line.add(testLineSplit[i]);
    }

    description.add(line);
    descGroup.add(description);     
}

This is NOT a constructor, just a method of the class that has the same name as class and is returning void.

In this case, as Java understands you are NOT providing any constructor, java provides a default one without parameters. In the test code, this default constructor is invoked, not your SourceClass method.

To fix it just remove 'void' from the constructor declaration.

edited May 7, 2015 at 11:08

forgivenson

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answered May 7, 2015 at 11:01

Alex Adas

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