Java - How to check if there is a value inside an ArrayList that is a value of a key in a HashMap?

Question

if (!mainMethods.matrix.isEmpty()) {
    for (int i = 0; i < mainMethods.matrix.values().size(); i++) {
        if (mainMethods.matrix.containsValue(getArrayList()[i].getValue().toString().contains(textValue.getText()))) {
            String errorTitle = "Impossível completar a operação.";
            String errorMessage = "Não é possível adicionar um valor de chave repetido.";
            JOptionPane.showMessageDialog(getParent(), errorMessage, errorTitle, JOptionPane.ERROR_MESSAGE);            
        }
    }

There is this HashMap called "matrix", and it has lots of keys. The value of every key is an ArrayList that has its own values. Considering this, I can't find a way to test whether there is a specic value inside the ArrayList-Values, because if I pass an String argument to the method ".containsValue()" of the HashMap, the method will find an ArrayList object and the test will be false. Therefore I must do something rather insane, just like I did in the example. As you can see, there's no such thing like "getArrayList()", or "getValue()". It's a very complicated situation and I tried to explain my point with "Pseudo-Code".

Do you know how to solve it?

Answer 1

If I understand you correctly, something like this ought to work:

private <K, V> V getValueIfKeyContains(final Map<List<K>, V> map, final K desiredKey) {
    for (final Entry<List<K>, V> entry : map.entrySet()) {
        if (entry.getKey().contains(desiredKey)) {
            return entry.getValue();
        }
    }
    return null;
}

So you loop over the Map and check whether each key contains the desiredKey .

I would strongly recommend two things:

1. Don't use mutable values as keys in a Map . This causes massive issues as they can change after they are added to the Map .
2. Don't use List if you want to check contains . This is an O(n) operation, ie it takes time proportional to the size of the List . It has to loop over every element in the List until it finds the right one. Use a Set and the operation becomes O(1) , ie constant time.

Answer 2

Do one thing. Change your data structure as...

Old one is:

HashMap <Key, ArrayList>

Change to

HashMap<Key, HashMap<Value in ArrayList at index[i], Value in ArrayList at index[i]>> .

This is assuming you have immutable objects inside the arrayList. So now once you get an object using key. You can again search in inner map using its keys.

Answer 3

You could use an iterator and check each arraylist individually:

Iterator it = mainMethod.matrix.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry pairs = (Map.Entry)it.next();
    If(pairs.getValue().contains(your value)
    {
        // do stuff
    }
}

Answer 4

Use a for-each loop to iterate over your ArrayList s (I've assumed they hold String s) and use their contains() method to test if a value is present within or not.

if (!mainMethods.matrix.isEmpty()) {
  for (List<String> list : mainMethods.matrix.values()) {
    if (list.contains(textValue.getText())) {
      String errorTitle="Impossível completar a operação.";
      String errorMessage="Não é possível adicionar um valor de chave repetido.";
      JOptionPane.showMessageDialog(
        getParent(), errorMessage, errorTitle, JOptionPane.ERROR_MESSAGE);
    }
  }
}

If possible switch to using a Set instead of a List as searching a set is many times faster. But sets won't allow you to have duplicates. So, choose what suits your requirements better.