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
– Lews Therin, Commented Jan 4, 2013 at 1:50
You can get a list of keys with myHashMap.keySet() if that's what you're asking. — ApproachingDarknessFish
– ApproachingDarknessFish, Commented Jan 4, 2013 at 1:52
Possible duplicate of How to efficiently iterate over each entry in a 'Map'? — BuZZ-dEE
– BuZZ-dEE, Commented Mar 12, 2018 at 13:29

Evgeniy Dorofeev · Accepted Answer · 2013-01-04 02:01:15Z

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 4, 2013 at 2:01

Evgeniy Dorofeev

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1 Comment

johnthagen Over a year ago

If you want immutable access to the Entry, make e final.

ruakh · Accepted Answer · 2013-01-04 01:51:18Z

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 4, 2013 at 1:51

ruakh

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Thirumal · Accepted Answer · 2016-10-19 07:38:09Z

12

Only in Java 8 & above

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

answered Oct 19, 2016 at 7:38

Thirumal

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mfsiega · Accepted Answer · 2013-01-04 01:51:29Z

1

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.

answered Jan 4, 2013 at 1:51

mfsiega

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