rkhachatryan commented on code in PR #22788:
URL: https://github.com/apache/flink/pull/22788#discussion_r1235431867
##########
flink-core/src/main/java/org/apache/flink/util/CollectionUtil.java:
##########
@@ -133,4 +140,71 @@ public static <K, V> Map<K, V> map(Map.Entry<K, V>...
entries) {
}
return Collections.unmodifiableMap(map);
}
+
+ /**
+ * Creates a new {@link HashMap} of the expected size, i.e. a hash map
that will not rehash if
+ * expectedSize many keys are inserted, considering the load factor.
+ *
+ * @param expectedSize the expected size of the created hash map.
+ * @return a new hash map instance with enough capacity for the expected
size.
+ * @param <K> the type of keys maintained by this map.
+ * @param <V> the type of mapped values.
+ */
+ public static <K, V> HashMap<K, V> newHashMapWithExpectedSize(int
expectedSize) {
+ return new HashMap<>(computeRequiredCapacity(expectedSize),
HASH_MAP_DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Creates a new {@link LinkedHashMap} of the expected size, i.e. a hash
map that will not
+ * rehash if expectedSize many keys are inserted, considering the load
factor.
+ *
+ * @param expectedSize the expected size of the created hash map.
+ * @return a new hash map instance with enough capacity for the expected
size.
+ * @param <K> the type of keys maintained by this map.
+ * @param <V> the type of mapped values.
+ */
+ public static <K, V> LinkedHashMap<K, V>
newLinkedHashMapWithExpectedSize(int expectedSize) {
+ return new LinkedHashMap<>(
+ computeRequiredCapacity(expectedSize),
HASH_MAP_DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Creates a new {@link HashSet} of the expected size, i.e. a hash set
that will not rehash if
+ * expectedSize many unique elements are inserted, considering the load
factor.
+ *
+ * @param expectedSize the expected size of the created hash map.
+ * @return a new hash map instance with enough capacity for the expected
size.
+ * @param <E> the type of elements stored by this set.
+ */
+ public static <E> HashSet<E> newHashSetWithExpectedSize(int expectedSize) {
+ return new HashSet<>(computeRequiredCapacity(expectedSize),
HASH_MAP_DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Creates a new {@link LinkedHashSet} of the expected size, i.e. a hash
set that will not
+ * rehash if expectedSize many unique elements are inserted, considering
the load factor.
+ *
+ * @param expectedSize the expected size of the created hash map.
+ * @return a new hash map instance with enough capacity for the expected
size.
+ * @param <E> the type of elements stored by this set.
+ */
+ public static <E> LinkedHashSet<E> newLinkedHashSetWithExpectedSize(int
expectedSize) {
+ return new LinkedHashSet<>(
+ computeRequiredCapacity(expectedSize),
HASH_MAP_DEFAULT_LOAD_FACTOR);
+ }
+
+ /**
+ * Helper method to compute the right capacity for a hash map with load
factor
+ * HASH_MAP_DEFAULT_LOAD_FACTOR.
+ */
+ @VisibleForTesting
+ static int computeRequiredCapacity(int expectedSize) {
Review Comment:
Yes, but why one should keep that in mind? How do we ensure this contract
throughout the lifecycle of this class?
Let me clarify what I'm proposing - the call site would look like this:
```
new HashMap<>(
computeRequiredCapacity(
expectedSize,
HASH_MAP_DEFAULT_LOAD_FACTOR),
HASH_MAP_DEFAULT_LOAD_FACTOR
);
```
Are there any disadvantages of doing that?
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