how can i convert hashmap to array?

Question

I want to convert hashMap (String,Integer) such as String[], Integer[].

But I heard the information about hashmap.keyset().array() and hashmap.values().array() doesn't match, so it is dangerous,

then, is it possible?

        for(Map.Entry<String,Integer> val: hashmap.entrySet()) {
            int n = 0;
            String key[n]=val.getKey();
            int value[n]=val.getValue();
            n++;
        }

Why do you want to do this? The pattern you mention is called parallel arrays, and it is usually better to go to effort not to do that in the first place. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Nov 28, 2021 at 6:42
Now I am making an application which counts the number of user's watching record and put it order by genre, so i need each array and put it in chart — JPep26
– JPep26, Commented Nov 28, 2021 at 6:54

Stephen C · Accepted Answer · 2021-11-28 06:17:09Z

2

If you want to convert it to a single array then:

Object[] array = hashmap.entrySet().toArray();

or

Map.Entry<String, Integer>[] array = 
        hashmap.entrySet().toArray(Map.Entry<?, ?>[0]);

(Possibly an unchecked conversion is required, but it is safe ...).

If you want parallel arrays for the keys and values:

String[] keys = new String[hashmap.size()];
Integer[] values = new Integer[hashmap.size()];
int i = 0;
for (e: hashmap.entrySet()) {
    keys[i] = e.getKey();
    values[i] = e.getValue();
    i++;
}

There is probably a neater solution using the Java 8+ stream functionality.

answered Nov 28, 2021 at 6:17

Stephen C

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