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/04-defensive-copy-record.txt

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+=== LeakyOrder: a record field that LOOKS immutable but isn't ===
+leaky.items() right after construction = [widget, gadget]
+caller mutates their OWN list reference afterwards: callerList.add(...)
+leaky.items() now                        = [widget, gadget, SNEAKY EXTRA ITEM]  <- the record's field changed too, because it's the SAME list object
+
+=== LeakyOrder.items() also returns the live mutable reference - callers can mutate it directly ===
+leaky.items() after leaky.items().add(...) = [widget, gadget, SNEAKY EXTRA ITEM, MUTATED THROUGH THE ACCESSOR]
+
+=== SafeOrder: List.copyOf(...) in a compact constructor closes both holes ===
+safe.items() right after construction = [widget, gadget]
+caller mutates their OWN list reference afterwards: callerList2.add(...)
+safe.items() now                       = [widget, gadget]  <- unchanged, it's an independent copy
+
+=== And the accessor's result rejects mutation too, since List.copyOf returns an immutable list ===
+safe.items().add(...) threw UnsupportedOperationException
+
+=== The constructor itself still rejects null elements, same as List.of ===
+new SafeOrder(..., listContainingNull) threw NullPointerException from inside List.copyOf(...)