How to replace ALL keys in java map?

Question

I want to replace keys in my map.

I have the following code:

Map<String, Object> map = new HashMap<String, Object>();
map.put("a", "1");
map.put("b", "2");
map.put("c", "3");
map.put("d", "4");
map.put("e", "5");
Iterator<Map.Entry<String, Object>> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
    Map.Entry<String, Object> next = iterator.next();
    Object o = next.getValue();
    //how to add new element ?
    //...
    iterator.remove();
}

I want to achieve map with keys

a1->1
b2->2
c3->3
d4->4
e5->5

If I use in loop map.put(next.getKey() + next.getValue(), next.getValue()); it will lead to ConcurrentModificationException.

Do we have guarantee that new key doesn't already exist in map? Also are you facing any specific problem when writing your code? — Pshemo, Jul 01 '16 at 14:33
Is this some kind of testing account that tracks the moderation of the forum? — Kayaman, Jul 01 '16 at 14:34
@pandaadb really? Surely it will replace the previous *value*? — Andy Turner, Jul 01 '16 at 14:34
Do you must modify existing map? Or can you return new one with updated key-value pairs? — Pshemo, Jul 01 '16 at 14:35
@Sotirios Delimanolis answer you attach as duplicate contains answer how to replace 1 key(instead of all) — gstackoverflow, Jul 01 '16 at 14:52
I changed duplicate target since your question was more detailed. — Pshemo, Jul 01 '16 at 15:07

score 3 · Accepted Answer · answered Jul 01 '16 at 14:36

To avoid a ConcurrentModificationException, you need to add the new key/value pairs to a separate map, and then use putAll to add that map into the original one.

    Map<String, Object> newMap = new HashMap<>();
    while (iterator.hasNext()) {
        Map.Entry<String, Object> entry = iterator.next();
        iterator.remove();
        newMap.put(...);  // Whatever logic to compose new key/value pair.
    }
    map.putAll(newMap);

How to replace ALL keys in java map?

1 Answers1