BAEL-9417 Improvement (#18739)

Co-authored-by: Wynn Teo <[email protected]>

Author: wynnteo

core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java

@@ -1,24 +1,23 @@
 package com.baeldung.streams.gatherer;
 
-import java.util.ArrayList;
-import java.util.List;
+import java.util.*;
 import java.util.function.BiConsumer;
 import java.util.function.Supplier;
 import java.util.stream.Gatherer;
 
-public class SlidingWindowGatherer implements Gatherer<Integer, ArrayList<Integer>, List<Integer>> {
+public class SlidingWindowGatherer implements Gatherer<Integer, Deque<Integer>, List<Integer>> {
 
     @Override
-    public Supplier<ArrayList<Integer>> initializer() {
-        return ArrayList::new;
+    public Supplier<Deque<Integer>> initializer() {
+        return ArrayDeque::new;
     }
 
     @Override
-    public Integrator<ArrayList<Integer>, Integer, List<Integer>> integrator() {
+    public Integrator<Deque<Integer>, Integer, List<Integer>> integrator() {
         return new Integrator<>() {
             @Override
-            public boolean integrate(ArrayList<Integer> state, Integer element, Downstream<? super List<Integer>> downstream) {
-                state.add(element);
+            public boolean integrate(Deque<Integer> state, Integer element, Downstream<? super List<Integer>> downstream) {
+                state.addLast(element);
                 if (state.size() == 3) {
                     downstream.push(new ArrayList<>(state));
                     state.removeFirst();
@@ -29,12 +28,7 @@ public boolean integrate(ArrayList<Integer> state, Integer element, Downstream<?
     }
 
     @Override
-    public BiConsumer<ArrayList<Integer>, Downstream<? super List<Integer>>> finisher() {
-        return (state, downstream) -> {
-            if (state.size()==3) {
-                downstream.push(new ArrayList<>(state));
-            }
-        };
-
+    public BiConsumer<Deque<Integer>, Downstream<? super List<Integer>>> finisher() {
+        return (state, downstream) -> {};
     }
 }