Java - How to access an ArrayList that is inside a method's scope, from another method?

Question

Yes, I know that's impossible; but the problem is that I really need to do it. I'll explain the whole trap:

public class MainMethods {

ArrayList arrayOfValues; // << PROBLEM

HashMap<String, Object> matrix = new HashMap<String, Object>();

void sendKeyToMatrix(String key) {
    arrayOfValues = new ArrayList();
    matrix.put(key, arrayOfValues);
}

void attachValueToKey(Object object, Object value) {
    matrix.put((String) object, arrayOfValues.add(value));
}

void removeFromMatrix(String key) {
    matrix.remove(key);
}}

That's my class and those are my methods. I created a HashMap with the key being a String and its value being an Object; pretty simple.

The real problem is with what I intend to do with this "Object" as a value. I have a GUI and a button that calls the "sendKeyToMatrix", and another one that attach a value to it, both from textFields. Since the ".put()" method for HashMaps requires an Object and I must create only the key first, the second argument is "null" or THE PROBLEM (ArrayList).

The perfect solution:

public class MainMethods {

HashMap<String, Object> matrix = new HashMap<String, Object>();

void sendKeyToMatrix(String key) {
    ArrayList arrayOfValues = new ArrayList();
    matrix.put(key, arrayOfValues);
}

void attachValueToKey(Object object, Object value) {
    matrix.put((String) object, ghostOrigin.add(value));
}

void removeFromMatrix(String key) {
    matrix.remove(key);
}}

When I call the "sendKeytoMatrix" with the button, it creates a key with an empty ArrayList as its value. This key is added to my JList. Then, when I call the second button (Considering what is selected in the JList), I add an element to the ArrayList:

Code for the second button:

btnInsertContent.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            mainMethods.attachValueToKey(mainList.getSelectedValue(), textContent.getText());
            mainCombo.addItem(textContent.getText());
            System.out.println(mainMethods.matrix);

        }
    });

The second argument of the "attachValueToKey" receives the String given by the textField, and I reach the big problem:

I can't add it to the ArrayList inside the "sendKeyToMatrix" method, which is obvious, but that's a big problem, because if I declare the variable as a field up there (So that I can access it down in the other scope), I get wrong and esoterically misterious results that are unknown to me.

Resuming this in a simple question: How to access the variable inside the other method?

If I declare the variable inside the "attachValueToKey", it will create an ArrayList inside of the ArrayList every time the button is pressed.

Well, I thank you all for the help. Probably there must be a way to summon the solution through Object Oriented Magic, with instances and the like.

Your post is too long that can't be read, please be very specific on telling the problem. — Azad
– Azad, Commented May 4, 2013 at 18:25

Ali Alavi · Accepted Answer · 2013-05-04 18:23:25Z

2

Something like this should answer your question I suppose:

void attachValueToKey(Object object, Object value) {
    ArrayList a = matrix.get((String) object);
    a.add(value));
}

answered May 4, 2013 at 18:23

Ali Alavi

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Comments

Ericson Willians · Accepted Answer · 2013-05-04 19:19:57Z

For learning purposes, I'll leave here the solution I found thanks to Lazarus:

public class MainMethods {

HashMap<String, Object> matrix = new HashMap<String, Object>();

void sendKeyToMatrix(String key) {
    ArrayList<Object> arrayOfValues = new ArrayList<Object>();
    matrix.put(key, arrayOfValues);
}

void attachValueToKey(Object object, String value) {
    ArrayList<String> arrayInMatrix = (ArrayList<String>) matrix.get(object);
    arrayInMatrix.add(value);
    matrix.put((String) object, arrayInMatrix);
}

void removeFromMatrix(String key) {
    matrix.remove(key);
} }

Action of the Button:

btnInsertContent.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            mainMethods.attachValueToKey(mainList.getSelectedValue(), textContent.getText());
            mainCombo.addItem(textContent.getText());
            System.out.println(mainMethods.matrix);

        }
    });

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