What is the equivalent of a Java HashMap in Swift

Question

I have an example written in Java that I would like to convert into Swift. Below is a section of the code. I would really appreciate if you can help.

Map<String, Integer> someProtocol = new HashMap<>();
someProtocol.put("one", Integer.valueOf(1));
someProtocol.put("two", Integer.valueOf(2));

for (Map.Entry<String, Integer> e : someProtocol.entrySet() {
    int index = e.getValue();
    ...
}

NOTE: entrySet() is a method of the java.util.Map interface whereas getValue() is a method of the java.util.Map.Entry interface.

I have tried to declare someProtocol as NSMutableDictionary but I had difficulties running it through the for loop. — Juventus, Jun 19 '17 at 19:22
You shouldn't convert Java to Swift on a line by line level. That limits your code to only using those features in Swift that have a Java analogue. That's a severe restriction that leads to crappy (Java-level) code. You should instead look at what problem the Java code is solving, and then find the best way of soling that problem in Swift. This technique leads to almost universally better code. — Alexander, Jun 19 '17 at 19:32
OP never said he wants to convert it line by line though. For example, I'm looking for the same thing as OP, and I stumbled onto this. The same or similar approach in a different language has being given to me in the answers - so I'd say it's a valid question as well as a valid problem. +1 — milosmns, Apr 10 '20 at 16:15

score 71 · Accepted Answer · edited Jun 19 '17 at 19:32

71

I believe you can use a dictionary. Here are two ways to do the dictionary part.

var someProtocol = [String : Int]()
someProtocol["one"] = 1
someProtocol["two"] = 2

or try this which uses type inference

var someProtocol = [
    "one" : 1,
    "two" : 2
]

as for the for loop

var index: Int
for (e, value) in someProtocol  {
    index = value
}

edited Jun 19 '17 at 19:32

Boghyon Hoffmann

17,103
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answered Jun 19 '17 at 19:13

Dew Time

818
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1

Yep, that's exactly right. I would omit the first code snippet though, as that's a Swift anti pattern (that's especially common for Java programmers who don't know there are literals). Also, `index` should be a variable in the scope of the `for` loop. – Alexander Jun 19 '17 at 19:27
1

Thank you for providing this response, it really help me out. – Juventus Jun 22 '17 at 11:36
what about `LinkedHashMap`? – user924 Mar 28 '19 at 20:46

Alexander · Answer 2 · 2017-06-19T19:32:36.977

6

let stringIntMapping = [
    "one": 1,
    "two": 2,
]

for (word, integer) in stringIntMapping {
    //...
    print(word, integer)
}

edited Jun 19 '17 at 19:32

answered Jun 19 '17 at 19:29

Alexander

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If you are being idiomatic then a `let` might be better than a `var` ;) – Paulo Mattos Jun 19 '17 at 19:32
@PauloMattos Good catch – Alexander Jun 19 '17 at 19:32
To reduce confusion between the Java map signature of the OP (`Map`) and the equivalent in Swift, it should be`String` for the keys (`[String: Int]`) instead of `word`. – Jack G. Jun 19 '17 at 19:58

Mykola Yashchenko · Answer 3 · 2017-06-19T19:33:54.067

3

I guess it will be something like that:

let someProtocol = [
    "one" : 1,
    "two" : 2
]

for (key, value) in someProtocol {
    var index = value
}

edited Jun 19 '17 at 19:33

answered Jun 19 '17 at 18:53

Mykola Yashchenko

5,103
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You don't need the type annotation on `someProtocol`. You should also rename `someProtocol` and make it a `let` constant – Alexander Jun 19 '17 at 19:33
I left the same name for a dictionary as mentioned in Java code. – Mykola Yashchenko Jun 19 '17 at 19:35

What is the equivalent of a Java HashMap in Swift

3 Answers3

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