For each loop on Java HashMap

Question

A basic chat program I wrote has several key words that generate special actions, images, messages, etc. I store all of the key words and special functions in a HashMap. Key words are the keys and functions are the values. I want to compare user input to the keys with some type of loop. I have tried everything I can think of and nothing works. This is what I can figure out:

myHashMap = <File Input>
for(String currentKey : <List of HashMap Keys>){
    if(user.getInput().equalsIgnoreCase(currentKey)){
        //Do related Value action
    }
}
...

I would appreciate any help. Forgive me if I overlooked a similar question or if the answer is obvious.

How are you storing a function in a Hashmap? Do you mean a listener? — Lews Therin, Jan 04 '13 at 01:50
You can get a list of keys with `myHashMap.keySet()` if that's what you're asking. — ApproachingDarknessFish, Jan 04 '13 at 01:52
Possible duplicate of [How to efficiently iterate over each entry in a 'Map'?](https://stackoverflow.com/questions/46898/how-to-efficiently-iterate-over-each-entry-in-a-map) — BuZZ-dEE, Mar 12 '18 at 13:29

score 70 · Answer 1 · answered Jan 04 '13 at 02:01

70

If you need access to both key and value then this is the most efficient way

    for(Entry<String, String> e : m.entrySet()) {
        String key = e.getKey();
        String value = e.getValue();
    }

answered Jan 04 '13 at 02:01

Evgeniy Dorofeev

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1

If you want immutable access to the `Entry`, make `e` `final`. – phoenix Sep 27 '17 at 13:50

score 24 · Accepted Answer · answered Jan 04 '13 at 01:51

24

Well, you can write:

for(String currentKey : myHashMap.keySet()){

but this isn't really the best way to use a hash-map.

A better approach is to populate myHashMap with all-lowercase keys, and then write:

theFunction = myHashMap.get(user.getInput().toLowerCase());

to retrieve the function (or null if the user-input does not appear in the map).

answered Jan 04 '13 at 01:51

ruakh

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I keep coming back to this answer. Thanks! – Chef1075 Nov 27 '17 at 04:08

score 12 · Answer 3 · answered Oct 19 '16 at 07:38

12

Only in Java 8 & above

map.forEach((k,v)->System.out.println("Key: " + k + "Value: " + v));

answered Oct 19 '16 at 07:38

Thirumal

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score 1 · Answer 4 · answered Jan 04 '13 at 01:51

A better pattern here might be:

Value val = hashMap.get(user.getInput());
if (val != null) {
    doVal();
}
else {
    // handle normal, non-keyword/specfial function
}

which takes advantage of the fact that HashMap returns null if the key isn't contained in the Map.

For each loop on Java HashMap

4 Answers4

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