Map to TreeMap

Question

I have a Map<String, String> object. I want to have it sorted by the keys, but the keys should be seen as integer. I just created an TreeMap<Integer, String>(myMapObject).

But this obviously does not work. How can I create a new TreeMap and change the keys from String to Integer?

Please provide more example code... Do you have just a `Map` or an object containing that structure? Can't you implement some POJO that `implements Comparable`? — deHaar, Aug 08 '18 at 08:15
which version of java do you use. and are these keys convertable to Integer ? — pvpkiran, Aug 08 '18 at 08:19
@deHaar OP has already given the map signatures. Its not POJO, just String and Integer classes. But yes as suggested use a simple comparator which convert String to Integer internally. — Himanshu Bhardwaj, Aug 08 '18 at 08:20

score 3 · Accepted Answer · edited Aug 08 '18 at 08:20

You can use Collectors.toMap in Java 8:

Map<Integer, String> map1 = map.entrySet().stream().collect(Collectors.toMap(entry -> Integer.parseInt(entry.getKey()), Map.Entry::getValue, (a, b) -> b));

Or below traditional approach:

Map<Integer, String> map1 = new HashMap<>();

for(final Map.Entry<String, String> entry : map.entrySet()){
     map1.put(Integer.parseInt(entry.getKey()), entry.getValue());
}

Map to TreeMap

1 Answers1