CODEWITHSUNDEEP
java
Metadata
Metadata

Reputation: 2083

How to retrieve common key value pairs from two hashmaps

I have two hashmaps:

Map<String, String> mapA = new HashMap<String, String>();
Map<String, String> mapB = new HashMap<String, String>();
TreeSet<String> uniquekeys = new TreeSet<String>();
mapA.put("1","value1");
mapA.put("2","value2");
mapA.put("3","value3");
mapA.put("4","value4");
mapA.put("5","value5");
mapA.put("6","value6");
mapA.put("7","value7");
mapA.put("8","value8");
mapA.put("9","value9");
mapB.put("1","value1");
mapB.put("2","value2");
mapB.put("3","value3");
mapB.put("4","value4");
mapB.put("5","value5");

To get the common key value pairs from the two hashmaps, I have written the below logic:

uniquekeys.addAll(mapA.keySet());
uniquekeys.addAll(mapB.keySet());

and then use the keys from the treeset: uniquekeys to retrieve unique key value pairs from mapA & mapB. But this is not giving me the details of all the keys from mapA. I understand this way is flawed but I couldn't come up with a proper logic. Could anyone let me know how can I retrieve key value pairs that are common in mapA and mapB into a new HashMap ?

Upvotes: 2

Views: 2428

Answers (4)

NiVeR
NiVeR

Reputation: 9786

You can do it with Java 8 Streams in the following way:

Map<String, String> commonMap = mapA.entrySet().stream()
        .filter(x -> mapB.containsKey(x.getKey()))
        .collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue()));

Upvotes: 2

linuxlsx
linuxlsx

Reputation: 138

Use Guava Util Sets

Set<String> intersectionSet = Sets.intersection(firstSet, secondSet);

Upvotes: 0

Kepotx
Kepotx

Reputation: 1082

Instead of adding all keys to a TreeSet, you can fill the TreeSet with common values:

uniquekeys.addAll(mapA.keySet());
uniquekeys.retainAll(mapB.keySet());

This way, the keys contained in A but not B will be removed. Know you've got your TreeSet, you can do what you want.

However, you can also create your HashMap without TreeSet, as @Ramesh and @NiVeR suggest

Upvotes: 0

Ramesh
Ramesh

Reputation: 340

Try below logic :

Map<String, String> common = new HashMap<String, String>();
        for(String key : mapA.keySet()) {
            if(mapB.get(key) !=null ) {
                if(mapA.get(key).equals(mapB.get(key))) {
                    common.put(key, mapA.get(key));
                }
            }
        }

Upvotes: 2

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