[GitHub] [wicket] solomax commented on a diff in pull request #513: More efficient hashcode computations

[GitBox <gi...@apache.org>]

solomax commented on code in PR #513:
URL: https://github.com/apache/wicket/pull/513#discussion_r853968190


##########
wicket-core/src/main/java/org/apache/wicket/markup/head/AbstractJavaScriptReferenceHeaderItem.java:
##########
@@ -135,6 +135,16 @@ public boolean equals(Object o)
 	@Override
 	public int hashCode()
 	{
-		return Objects.hash(async, defer, charset);
+		// original code was: return Objects.hash(async, defer, charset);
+		// This returns the same hash code value, but doesn't allocate an Object[3],
+		// which consumes 32 bytes, and doesn't need to autobox the two booleans.
+		// This method is called very often, especially when a containing Map or Set is resized,
+		// and this version will run faster and save a lot of memory.
+		// It is possible that Escape Analysis would elide the creation of the Object[],
+		// but we do not see that in our running applications with the latest JDK.
+		return 31*31*31 +
+				31*31*Boolean.hashCode(async) +
+				31*Boolean.hashCode(defer) +
+				((charset != null) ? charset.hashCode() : 0);

Review Comment:
   `hash` method from here https://docs.oracle.com/javase/8/docs/api/java/util/Objects.html can also be used :)



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