Java - using Map how to find matching Key when Values are stored a List of strings

Question

All,

I have a map with categories and subcategories as lists like this:

    Map> cat = new HashMap

        

Answer 1

You have to search for the value in the entire map:

for (Entry<String, List<String>> entry : cat.entrySet()) {
    for (String s : entry.getValue()) {
        if (s.equals("Carrot"))
            System.out.println(entry.getKey());
    }
}

Answer 2

You need to create the inversed map:

Map<String, String> fruitCategoryMap = new HashMap<>();
for(Entry<String, List<String>> catEntry : cat.entrySet()) {
    for(String fruit : catEntry.getValue()) {
        fruitCategoryMap.put(fruit, catEntry.getKey());
    }
}

Then you can simply do:

String category = fruitCategoryMap.get("Banana"); // "Fruit"

Answer 3

Iterate thought all the keys and check in the value if found then break the loop.

for (String key : cat.keySet()) {
    if (cat.get(key).contains("Carrot")) {
        System.out.println(key + " contains Carrot");
        break;
    }
}

Answer 4

try this,

for (Map.Entry<String, List<String>> entry : cat.entrySet()) {
        String names[] = entry.getValue().toArray(new String[entry.getValue().size()]);
        for (int i = 0; i < names.length; i++) {
            if (names[i].equals("Carrot")) {
                System.out.println("found"+names[i]);
                break;
            } 
        }

    }