error: Object cannot be converted to String

Question

Does anyone have any help with this error?

error: incompatible types: Object cannot be converted to String

I am passing a HashMap into a function with the intention of iterating through its keyset and storing them into a list for ordering, here is my code

public HashMap mapReorder(HashMap map) {

    /* Clear the list ready for input */
    mapList.clear();

    /* Iterate through the keys in the map */

    for(String keys : map.keySet()) {
        double mapKey = keys.getValue();
        mapList.add(mapKey);
    }

    /* Sorting the order by ascending value (Internal Frequency Rank) */
    Collections.sort(mapList);

    /* Populating HashMap with ordered list */
    for(double frequencies : mapList) {
        orderedMap.put(keys , frequencies);
    }

    return null;
}

Have you googled your error message ? You will find your answer. — Romain Hippeau, Dec 14 '17 at 12:05
See also: https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it — Yoory N., Dec 14 '17 at 12:17

Lino · Answer 1 · 2017-12-14T12:19:59.263

2

the line with for(String keys : map.keySet()) is causing the error.

Map.keySet() returns a Set<Object> and not a Set<String> because you're using rawTypes (HashMap). So change either the line to:

for(Object keys : map.keySet())

or change the signature of your method to following:

public HashMap<String, ValueType> mapReorder(HashMap<String,ValueType> map){

where ValueType is the type of value stored in your map

edited Dec 14 '17 at 12:19

answered Dec 14 '17 at 12:05

Lino

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This is wrong. You can use the enhanced loop to iterate over a `Set`. – Murat Karagöz Dec 14 '17 at 12:07
@MuratK. sorry had a brainfart. see the edit – Lino Dec 14 '17 at 12:20

ThomasEdwin · Answer 2 · 2017-12-14T12:15:29.507

-2

I am passing a hashmap into a function with the intention of iterating through its keyset and storing them into a list for ordering

HashMap is not ordered. So you better use TreeMap which is sorted according to natural ordering of its keys.

return new TreeMap(map)

edited Dec 14 '17 at 12:15

answered Dec 14 '17 at 12:07

ThomasEdwin

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This does not even answer the question remotely. – Murat Karagöz Dec 14 '17 at 12:10
I offer a better way @MuratK. The code in question is wrong. The TS want to sort the map, using `HashMap` which is not sorted. – ThomasEdwin Dec 14 '17 at 12:11
I'm waiting for one more downvote :) – ThomasEdwin Dec 18 '17 at 11:50

error: Object cannot be converted to String

2 Answers2