Amar Dwivedi Jr. Amar Dwivedi Jr. - 1 year ago 73
Java Question

Should we traverse map? Why?

If we are using map,I think there is no need for traverse object by for each loop or other way. We have a unique key and value so we can easily find value.
I faced this question so many time in interview. I don't think so this question is
correct. Please help me in regarding question.

Answer Source

You should traverse a map when ... you need to traverse a map. You're correct that if you have a key, you don't need to do any traversal; just use the key. But there are times you don't have a key. For instance, imagine a map keyed by people's names with their ages as values:

Map<String, Integer> m = new HashMap<String, Integer>();
// Presumably these are added by a user or similar
m.put("Joe", 27);
m.put("Mohammad", 42);
m.put("Maria", 29);

Later we need to output all the names and ages; we'll traverse the map (more technically, we'll traverse its entry set):

for (Map.Entry<String, Integer> e : m.entrySet()) {
    System.out.println(e.getKey() + ": " + e.getValue());

Other times we might traverse keySet or values.

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