From 3d99ba9c817ce0106a0ecbadafb8d6df92950d67 Mon Sep 17 00:00:00 2001
From: soyeon1806 <ksy1118s@naver.com>
Date: Mon, 27 Jul 2026 02:03:59 +0900
Subject: [PATCH] Fix broken sliding window logic in SlidingWindowGatherer

Commit aae2714723 removed the `state.size() == 3` guard from the
integrator. Without it, every element is pushed downstream and then
immediately dropped, so the gatherer emits one single-element list per
input instead of overlapping windows of three.

For the stream 1..5, SlidingWindowGathererUnitTest expects
[[1, 2, 3], [2, 3, 4], [3, 4, 5]], but the current code produces
[[1], [2], [3], [4], [5]] and fails on the window-count assertion.

Restoring the guard also lets the finisher() override go away: it
returned an empty BiConsumer, which is exactly what the default
finisher of Gatherer already does.

Refs #18683
---
 .../streams/gatherer/SlidingWindowGatherer.java      | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java
index 713d88e0e2a1..90d5b2eed747 100644
--- a/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java
+++ b/core-java-modules/core-java-streams-7/src/main/java/com/baeldung/streams/gatherer/SlidingWindowGatherer.java
@@ -1,7 +1,6 @@
 package com.baeldung.streams.gatherer;
 
 import java.util.*;
-import java.util.function.BiConsumer;
 import java.util.function.Supplier;
 import java.util.stream.Gatherer;
 
@@ -18,15 +17,12 @@ public Integrator<Deque<Integer>, Integer, List<Integer>> integrator() {
             @Override
             public boolean integrate(Deque<Integer> state, Integer element, Downstream<? super List<Integer>> downstream) {
                 state.addLast(element);
-                downstream.push(new ArrayList<>(state));
-                state.removeFirst();
+                if (state.size() == 3) {
+                    downstream.push(new ArrayList<>(state));
+                    state.removeFirst();
+                }
                 return true;
             }
         };
     }
-
-    @Override
-    public BiConsumer<Deque<Integer>, Downstream<? super List<Integer>>> finisher() {
-        return (state, downstream) -> {};
-    }
 }