Lambda – merge different types of mappings into one in Java 8

There are two maps

>< integer, string > MAP1 is < ID, question > < integer, string > MAP2 is < ID, answer >

I want to merge them into a map < string, string > resultmap is < question, answer > so that the key in this map is the value in MAP1 (question), and the value in resultmap is the value in MAP2 (answer), which is based on the same ID

I can easily do this in Java 6, as shown in the following code

for(Map.Entry<Integer,String> entry:map1.entrySet()){
    qaMap.put(entry.getValue(),map2.get(entry.getKey()));
}

But I want to write this in Java 8 in Java and Lambdas How do you do it?

Solution

Assuming that your key (ID) is the same in two maps, we can do similar things

Map<String,String> map = map1.keySet().stream()
    .collect(Collectors.toMap(map1::get,map2::get));

>In the above statement, MAP1 keySet(). Stream() will provide you with the ID stream. > Then, the collectors. Tomap (MAP1:: get, MAP2:: get) will create a map from the ID stream, where the key is MAP1 Get (ID) (i.e. your question), the value is MAP2 Get (ID) (your answer) each ID