Java 8 Stream Filter Map With Multiple condition-CodePudding

Code Template:

Map<String, String> hashMap = new HashMap<>();    
hashMap.put("RED", "1");    
hashMap.put("BLUE", "2");    
hashMap.put("BLACK", "3");    

Map<String, String> filteredMap = hashMap.entrySet().stream()
.filter(entry -> (entry.getKey().equals("RED") && entry.getValue().equals("1"))  
**&&**
(entry.getKey().equals("BLUE") && entry.getValue().equals("2")) )
.collect(Collectors.toMap(map -> map.getKey(), map -> map.getValue()));

I want to find if the Map contains both {Red,1} and {Blue,2} inside it. How do I put both filters condition in a stream? I tried with && condition, but it's not working. Kindly help.

CodePudding user response：

Why do you want to use filter here at all? The filter over stream of entries shown in the question iterates through all the members of the map ( O(n) ) However, the HashMap guarantees O(1) access to "get" functionality. So why sacrifice performance here?

If you want to check whether the map contains a key (ok, two keys), why not simply:

if("1".equals(hashMap.get("RED")) && "2".equals(hashMap.get("BLUE"))) {
   // yes, this map indeed contains both elements 
   // in case the "RED" is not in the map, the call to "get" will return null
}

CodePudding user response：

Streams are not really appropriate for your problem. They are great for performing independent operations on members of a collection and then aggregating the results in some way. They are not great for functions on the collection as a whole or algorithms requiring interaction between members.

A much simpler formulation would be:

Objects.equals(map.get("RED"), "1") && Objects.equals(map.get("BLUE"), "2")

An alternative that avoids hardcoding the comparison would be:

Map<String, String> reference = Map.of("RED", "1", "BLUE", "2");

if (hashMap.entrySet().containsAll(reference.entrySet()) {
    ...
}