Create EnumMapDemo.java

rahulXbarnwal · web-flow · commit ce4b451c04bd · 2026-03-15T18:41:17.000+05:30
diff --git a/src/learnCollections/EnumMapDemo.java b/src/learnCollections/EnumMapDemo.java
@@ -0,0 +1,31 @@
+package learnCollections;
+
+import java.util.EnumMap;
+import java.util.Map;
+
+/*
+- if all the keys in Map are values of a single enum, it's recommended to use EnumMap. It has advantage of knowing all possible keys in advance 
+- it is more efficient compared to other implementations, as it internally uses a simple array
+ */
+
+public class EnumMapDemo {
+    public static void main(String[] args) {
+        // array of size same as enum
+        // [_, "Gym", _, _, _, _, _]
+        // no hashing
+        // ordinal / index is used
+        // faster than HashMap
+        // memory efficient
+        // ordered by enum declaration order
+        Map<Day, String> map = new EnumMap<>(Day.class);
+        map.put(Day.TUESDAY, "Gym");
+        map.put(Day.MONDAY, "Walk");
+        System.out.println(map); // {MONDAY=Walk, TUESDAY=Gym}
+
+        System.out.println(Day.TUESDAY.ordinal()); // 1 --> index
+    }
+}
+
+enum Day {
+    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
+}
