sequenced: JEP 431 Sequenced Collections across List/Deque/LinkedHashSet/LinkedHashMap/TreeMap, and the getLast() replacement for the Set find-last stream tricks

sequenced/output/01-across-collections-demo.txt

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+=== List (ArrayList implements SequencedCollection) ===
+getFirst()  = alpha
+getLast()   = gamma
+after addLast("delta"): [alpha, beta, gamma, delta]
+reversed()  = [delta, gamma, beta, alpha]
+
+=== Deque (ArrayDeque implements SequencedCollection) ===
+getFirst()  = 1
+getLast()   = 3
+reversed()  = [3, 2, 1]
+
+=== LinkedHashSet implements SequencedSet (insertion order preserved) ===
+getFirst()  = red
+getLast()   = blue
+reversed()  = [blue, green, red]
+
+=== LinkedHashMap implements SequencedMap (insertion order) ===
+firstEntry() = jan=1
+lastEntry()  = mar=3
+after putFirst("dec", 12): {dec=12, jan=1, feb=2, mar=3}
+sequencedKeySet() = [dec, jan, feb, mar]
+reversed()         = {mar=3, feb=2, jan=1, dec=12}
+
+=== TreeMap implements SequencedMap too (order = comparator order, not insertion) ===
+tree contents (natural order) = {1=one, 2=two, 3=three}
+firstEntry() = 1=one
+lastEntry()  = 3=three
+reversed()   = {3=three, 2=two, 1=one}