I want to get values for more than one key using HashMap
, for example:
HashMap<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Hello");
map.put(2, "World");
map.put(3, "New");
map.put(4, "Old");
Now I want to combine values for 1
and 2
and create a List<String>
output. I can do this with 2 times get an operation or create one function that takes a key list and return a list of values.
But is there any in-built util function that do the same job?
You can take an input Set
having the keys to query for and use stream operations Stream#filter
and Stream#map
to filter and map the results and finally collect the values into a list:
HashMap<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Hello");
map.put(2, "World");
map.put(3, "New");
map.put(4, "Old");
Set<Integer> keys = Set.of(1, 2);
List<String> values = map.entrySet()
.stream()
.filter(ent -> keys.contains(ent.getKey()))
.map(Map.Entry::getValue)
.collect(Collectors.toList());
System.out.println(values);
Output:
[Hello, World]
IntStream.of(1, 2)
.map(map::get)
.collect(Collectors.toList());
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