Java中的Hashmap内HashMap的值

Question

I have this hashmap of students which stores the id, name and last name. So I created this :

Map<Interger, HashMap<String,String>> students = new HashMap<>();

where the second hashmap stores the name and lastname. My goal is to look for a student in a swing application, I succeed in searching with id because it's the key of the first hashmap, but i'd like to use all of them like this:

So my question is : If I want to search by name or last name, how can i get the value of the first hashmap and put it in a new hashmap ?

Answer 1

You can iterate on the hashmap like this :

private int searchByName(String s) {
    for(Map.Entry<Integer, HashMap<String, String>> entry : students.entrySet()) {
        HashMap student = entry.getValue(); // Hashmap containing first and lastname
        if (student.containsKey(s)) // If name match
            return entry.getKey(); // Return the student ID
    }
    return 0; // Student not found
}

For the lastname just use containsValue(s) instead of containsKey(s)

Answer 2

You can use the Google Collections API Guava for that specifically a BiMap

A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as that of its keys. This constraint enables bimaps to support an "inverse view", which is another bimap containing the same entries as this bimap but with reversed keys and values.

With this you'will be able to search using first name and last name. This BiMap will be value to your first parent hashmap.

Answer 3

I am not sure if the data structure is the best for your use-case but answering to your question, you should try using values() method which would return you the collection of values of the Map

http://docs.oracle.com/javase/7/docs/api/java/util/HashMap.html#values()

Collection res =  studensts.values();

Iterator<HashMap<String, String>> i = res.iterator();
Map<String,String> resM = null;
while(i.hasNext()){
   resM = i.next();
}