在地图中检查密钥，增加新的密钥值并添加回地图

Question

I have entries in a LinkedHashMap<Integer,String> like:

1000 Coffee
2000 Source
3000 Legends
4000 Kaldi
4001 Sheikh Omar
3001 Transmission

The integer values are based on some hierarchy. Is there a way for me to check what was the last key in the 3000 or 2000 series in the map was so that my new key can be an increment of that? Eg If I need to make a new entry down the line at the 2000 hierarchy level and the last key was 2015, how can I check this and increment my new key to 2016 and add to the map.

Answer 1

You could use the streams API on the keyset like this:

 //floor is the start of the series, ceiling is the start of the next one.
 public Optional<Integer> getLastInSeries(int floor, int ceiling, LinkedHashMap<Integer, String> linkedHashMap) {
        return linkedHashMap.keySet().stream()
                .filter(integer -> integer < ceiling && integer > floor)
                .max(Comparator.naturalOrder());
    }

This returns an optional since you can't be sure that there is already a value in the series.

Answer 2

You can store the last key and increment it after adding new element or find it this way:

public int getLastKey(int series, LinkedHashMap map) {
    for(int i = 0; i < 1000; i++) {
        if (map.get(series + i) == null) {
            return series + i;
}

keySet() method of LinkedHashMap also might be helpful.