Java: Access the right map depending on variable without using "if"

Question

so that's my situation:

I have a method which gets a String and a bunch of other information. Depending on the content of the String, I want to put the other information into one of two Maps I have. Like this:

if (string.equals("A")) {
  A.put[..]
} else if (string.equals("B")) {
  B.put[..]
}

but because this situation happens a few times in my method, I don't want to use if/else every time because of redundancy.

Soo I guess what I need is some kind of object/pointer/reference which I can assign the Map I want to use once in the beginning and then use it as a placeholder.

So ... you want a conditional statement, without an actual conditional statement? .... — Stultuske
– Stultuske, Commented Jan 22, 2016 at 14:29
if it happens only a few times, you'd better leave the things as is. — AdamSkywalker
– AdamSkywalker, Commented Jan 22, 2016 at 14:35
@Stultuske I want less conditional statements, not noone. Which I realized using ctsts answer. — Jdv
– Jdv, Commented Jan 22, 2016 at 15:00

ctst · Accepted Answer · 2016-01-22 14:40:37Z

1

That's why we have reference variables:

Map<?,?> map;
if(string.equals("A"))
    map = A;
else if(string.equals("B"))
    map = B;
else
    map = new HashMap<>();

works fine. The last line is more like an error-check for your String and will be garbage collected after your method is finished (otherwise map might not be initialised, which would throw a NullPointer). After this you can put everything into map (thank reference variables :-) ). Remember map is just a reference to your Map A or B (or "void")

edited Jan 22, 2016 at 14:40

answered Jan 22, 2016 at 14:30

ctst

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1 Comment

Jdv Over a year ago

Wow, I've been writing stuff in Java for 3 years and didn't know that. Shame on me. Thanks!

Peter Lawrey · Accepted Answer · 2016-01-22 14:30:40Z

1

It appears you want a Map of Maps.

Map<String, Map<?, ?>> maps = new HashMap<>();

Map<?, ?> map = map.get(string);
map.put[...];

if you want to add the map as required you can use

Map<?, ?> map = map.computeIfAbsent(string, HashMap::new);

answered Jan 22, 2016 at 14:30

Peter Lawrey

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