How to sort Map values by key in Java?

Question

I have a Map that has strings for both keys and values.

Data is like following:

\"question1\", \"1\"
\"question9\", \"1\"
\"que

Answer 1

Provided you cannot use TreeMap, in Java 8 we can make use of toMap() method in Collectorswhich takes following parameters:

• keymapper: mapping function to produce keys
• valuemapper: mapping function to produce values
• mergeFunction: a merge function, used to resolve collisions between values associated with the same key
• mapSupplier: a function which returns a new, empty Map into which the results will be inserted.

Java 8 Example

Map sample = new HashMap<>();  // push some values to map  
Map newMapSortedByKey = sample.entrySet().stream()
                    .sorted(Map.Entry.comparingByKey().reversed())
                    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));
Map newMapSortedByValue = sample.entrySet().stream()
                        .sorted(Map.Entry.comparingByValue().reversed())
                        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1,e2) -> e1, LinkedHashMap::new));

We can modify the example to use custom comparator and to sort based on keys as:

Map newMapSortedByKey = sample.entrySet().stream()
                .sorted((e1,e2) -> e1.getKey().compareTo(e2.getKey()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1,e2) -> e1, LinkedHashMap::new));