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Collections beginner

Map.entry() factory

Create map entries with a clean factory method.

Code Comparison
✕ Java 8 
Map.Entry<String, Integer> e =
    new AbstractMap.SimpleEntry<>(
        "key", 42
    );
✓ Java 9+ 
var e = Map.entry("key", 42);
Why the modern way wins
📏

Concise

One line instead of three with a clearer intent.

🔒

Immutable

The returned entry cannot be modified.

🧩

Composable

Works perfectly with Map.ofEntries() for large maps.

Old Approach
SimpleEntry
Modern Approach
Map.entry()
Since JDK
9
Difficulty
beginner
JDK Support
Map.entry() factory
Available

Widely available since JDK 9 (Sept 2017)

How it works

Map.entry() replaces the verbose AbstractMap.SimpleEntry constructor. It returns an immutable entry, making it ideal for Map.ofEntries() and stream operations.

Related patterns

Collections beginner

Sequenced collections

Java 8
// Get last element
var last = list.get(list.size() - 1);
// Get first
var first = list.get(0);
// Reverse iteration: manual
Java 21+
var last = list.getLast();
var first = list.getFirst();
var reversed = list.reversed();
Hover to see modern ➜
JDK 21+ →
Collections beginner

Immutable map creation

Java 8
Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3);
map = Collections.unmodifiableMap(map);
Java 9+
Map<String, Integer> map =
    Map.of("a", 1, "b", 2, "c", 3);
Hover to see modern ➜
JDK 9+ →
Collections beginner

Immutable list creation

Java 8
List<String> list =
    Collections.unmodifiableList(
        new ArrayList<>(
            Arrays.asList("a", "b", "c")
        )
    );
Java 9+
List<String> list =
    List.of("a", "b", "c");
Hover to see modern ➜
JDK 9+ →
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