Java-检查嵌套在HashMap中的ArrayList中的值是否存在

Question

I have various ArrayList s nested in one HashMap .

How can I check if my array list nested in the hashmap exists?

public static HashMap<Integer, ArrayList<Integer>> transactionMap = new HashMap<Integer, ArrayList<Integer>>();

public static void initializeLists() {
    transactionMap.put(7, new ArrayList<Integer> (Arrays.asList(1050, 1125)));
    transactionMap.put(305, new ArrayList<Integer>(Arrays.asList(1125)));
    transactionMap.put(1125, new ArrayList<Integer>(Arrays.asList(250, 252, 251)));
    transactionMap.put(1050, new ArrayList<Integer>(Arrays.asList(251, 252)));
    transactionMap.put(1124, new ArrayList<Integer>(Arrays.asList(250)));
    transactionMap.put(1049, new ArrayList<Integer>(Arrays.asList(251, 252)));
}

This post here describes how to check directly in an Array List using #contains(Object) , which does not fit for HashMap .

This one is close but it would mean I would have to give a name to all my lists (and there could be many). I would like to avoid having to nest a map inside a map if possible unless needed. Does anyone have any points to the best solution?

Answer 1

If your question is "how do I check if a specific list is a value in the map" then you can do it as follows:

if (transactionMap.containsValue(Arrays.asList(1, 2, 3)) {
    ...
}

If your question is "how do I check if a specific integer appears somewhere in a list as a value in the map" then you can do the following (using Java 8):

if (transactionMap.values().stream().anyMatch(l -> l.contains(17)) {
    ...
}