sort a map by key

In Java, a Map does not guarantee ordering by default (e.g., HashMap). To sort a map by key, there are a few standard approaches depending on the situation.

 Map<String, Integer> map = new HashMap<>();
        map.put("Banana", 3);
        map.put("Apple", 1);
        map.put("Orange", 2);
        map.put("Grapes", 5);

1. Using TreeMap (Simplest)

TreeMap automatically sorts entries by key in natural order.

    public static Map<String, Integer> sortingByUsingTreeMap(Map<String, Integer> map){

        return new TreeMap<>(map);
    }

Result

{Apple=1, Banana=3, Grapes=5, Orange=2}

• TreeMap internally uses a Red-Black Tree
• Keys are sorted using natural ordering (Comparable).

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2. Using Java 8 Streams

Useful when you want sorted result but still return a Map.

    public static Map<String, Integer> sortingByUsingStreams(Map<String, Integer> map){

       return map.entrySet().stream()
                        .sorted(Map.Entry.comparingByKey())
                        .collect(Collectors.toMap(
                                Map.Entry::getKey,
                                Map.Entry::getValue,
                                (oldVal, newVal) -> oldVal,
                                LinkedHashMap::new
                        ));

    }

Why LinkedHashMap?

• Because it maintains insertion order, which preserves the sorted order.

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3. Reverse Order Sorting

If you want descending order by key.

 public static Map<String, Integer> sortingByUsingTreeMapInReverseOrder(Map<String, Integer> map){

        Map<String, Integer> sortedMap =  new TreeMap<>(Comparator.reverseOrder());

        sortedMap.putAll(map);

        return sortedMap;
    }

.sorted(Map.Entry.comparingByKey(Comparator.reverseOrder()))

Result

{Orange=2, Grapes=5, Banana=3, Apple=1}

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4. Using Custom Comparator

If sorting needs custom logic.

Map<String, Integer> sortedMap =
        new TreeMap<>((a, b) -> b.compareTo(a));

sortedMap.putAll(map);

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Approach	When to Use
TreeMap	When you always want sorted keys
Java 8 Streams	When sorting only once
Collections.reverseOrder()	When descending order required
Custom Comparator	When custom sorting logic needed