Java Collections

Question

I am adding the following to the HashMap collection after each row in the UI form

Declaration

Map<String, List<String>> map = new HashMap<String, List<String>>();
List<String> valSetOne = new ArrayList<String>();

Code snippet

 valSetOne.add("BMW");
 valSetOne.add("Audi");
 map.put("A1", valSetOne);

When I am in the second row in UI, I would like to check the above combination exist in the HashMap collection.

How can I check for the combination of values in each row?

• Kayaman: Use the containsValue() method?
• Jacob: @Kayaman Does contains check for entire row?
• Kayaman: You don't have rows. You have a Map of Lists. If you call containsValue(myList), it will check if myList is already contained within the values.
• Artur Biesiadowski: Consider looking at google.github.io/guava/releases/19.0/api/docs/com/google/common/… - it might simplify your list-in-map processing considerably and provide you with some helpful utility methods.
• Jacob: @ArturBiesiadowski Thanks for the suggestion. We do have a restriction in using third party libraries and due to this we wouldn't be able to external JAR files.

Answer 1

If you need performance with respect to checking if a value exists and dont care about the order in each row, you can use Set interface and use a HashSet instead of List

Map<String, Set<String>> map = new HashMap<String, Set<String>>();
Set<String> valSetOne = new HashSet<String>();

To check, use

Set<String> set= map.get("A1");//returns null if key does not exists(you also use containsKey() to check if key exists)
set.contains("value")

If you dont need performance, u can just use

List<String> valSetOne = new ArrayList<String>();
List<String> list = map.get("A1");//returns null if key does not exists(you also use containsKey() to check if key exists )
list .contains("value") to check if it exists

• Aditya K: You need to check for both the values separately either in list or in a set. but set gives better performance if u just want to check whether it exists or not and dont care about the order
• Jacob: Oh yes I got your point, for A1 key, the combination of Orange and Apple exists or not correct?
• Aditya K: yes. you need to run a loop to check whether orange as well as apple exists or not for A1
• Jacob: Thanks and much appreciated.

Answer 2

Depends on what you'd like to check for existence, there are two Map methods: containsKey and contiansValue.

need to check is key A1 there? -> use containsKey

need to check is there a list with Orange and Apple use -> containsValue

• Jacob: Thanks and much appreciated.