immutable: List.of vs unmodifiableList vs copyOf - null handling, views vs copies, JMH wrap/copy overhead, a Guava comparison, and the record defensive-copy trap

immutable/output/01-null-handling.txt

@@ -0,0 +1,21 @@
+=== List.of(...) - rejects null at construction time ===
+List.of("a", null, "c") threw NullPointerException
+
+=== Arrays.asList(...) - allows null, it's just a view over the array ===
+Arrays.asList("a", null, "c") = [a, null, c]
+
+=== Collections.unmodifiableList(...) - allows whatever the backing list allows ===
+unmodifiableList over a list already containing null = [a, null, c]
+(it has no null-check of its own - it only blocks structural writes, see below)
+
+=== List.copyOf(...) - rejects null, same as List.of ===
+List.copyOf(aListContainingNull) threw NullPointerException
+-> List.copyOf() re-validates elements, it does not just wrap and trust the source
+
+=== Collections.unmodifiableList is a VIEW, not a copy: mutating the backing list shows through ===
+before: unmodView = [a, null, c]
+after backing.set(0,...) and backing.add("d"): unmodView = [A-CHANGED, null, c, d]
+-> the "unmodifiable" promise is about the VIEW's own mutator methods, not about the data being frozen
+
+=== unmodifiableList's own mutators still throw, even though the backing list is mutable ===
+unmodView.add("e") threw UnsupportedOperationException