Java 25 (LTS) reference · 10 entries
Java Map and HashMap Methods
Map and HashMap methods: put(), get(), getOrDefault(), containsKey(), merge(), computeIfAbsent(), entrySet() and Map.of(), with counting and grouping examples.
HashMap has no defined order, so examples print through a TreeMap (sorted by key) or use a
LinkedHashMap (insertion order) to keep output predictable.
| Name | Description | Since |
|---|---|---|
Map.of() |
Create an immutable map from key-value pairs (up to 10 pairs; Map.ofEntries() for more). No null keys or values. | Java 9 |
map.put() |
Add a key-value pair, or replace the value if the key already exists. Returns the previous value or null. | Java 1.0 |
map.get() |
Return the value for a key, or null if the key isn't present. Use getOrDefault() to avoid nulls. | Java 1.0 |
map.getOrDefault() |
Return the value for a key, or a default value if the key isn't present. Avoids null checks. | Java 8 |
map.containsKey() |
Return true if the map has an entry for the key, even when its value is null. O(1) for HashMap. | Java 1.0 |
map.remove() |
Remove the entry for a key and return its value (or null). remove(key, value) only removes a matching pair. | Java 1.0 |
map.putIfAbsent() |
Add a key-value pair only if the key is missing (or mapped to null). Returns the existing value otherwise. | Java 8 |
map.merge() |
Combine a value into the map: insert it if the key is missing, otherwise apply a function to the old and new values. | Java 8 |
map.computeIfAbsent() |
Return the value for a key, creating and storing it with a function first if the key is missing. Ideal for grouping. | Java 8 |
map.entrySet() |
Return the map's entries (key-value pairs) for looping over keys and values together. | Java 1.0 |