make more gatherers null-aware

Author: jhspetersson

src/main/java/io/github/jhspetersson/packrat/DropLastNGatherer.java

@@ -1,7 +1,7 @@
 package io.github.jhspetersson.packrat;
 
-import java.util.ArrayDeque;
 import java.util.Deque;
+import java.util.LinkedList;
 import java.util.function.Supplier;
 import java.util.stream.Gatherer;
 
@@ -24,7 +24,7 @@ class DropLastNGatherer<T> implements Gatherer<T, Deque<T>, T> {
 
     @Override
     public Supplier<Deque<T>> initializer() {
-        return ArrayDeque::new;
+        return LinkedList::new;
     }
 
     @Override

src/main/java/io/github/jhspetersson/packrat/FixedSizeDeque.java

@@ -1,13 +1,15 @@
 package io.github.jhspetersson.packrat;
 
-import java.util.ArrayDeque;
 import java.util.Collection;
 import java.util.Deque;
 import java.util.Iterator;
+import java.util.LinkedList;
 
 /**
  * A fixed-size deque implementation that automatically removes the oldest element
  * when the maximum size is reached and a new element is added.
+ * <p>
+ * Backed by a {@link LinkedList} so that {@code null} elements are permitted.
  *
  * @param <E> the type of elements held in this deque
  * @author jhspetersson
@@ -27,7 +29,7 @@ public FixedSizeDeque(int maxSize) {
         }
 
         this.maxSize = maxSize;
-        this.delegate = new ArrayDeque<>(maxSize);
+        this.delegate = new LinkedList<>();
     }
 
     @Override

src/main/java/io/github/jhspetersson/packrat/LastingGatherer.java

@@ -1,9 +1,9 @@
 package io.github.jhspetersson.packrat;
 
-import java.util.ArrayDeque;
 import java.util.Deque;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.LinkedList;
 import java.util.Objects;
 import java.util.Set;
 import java.util.function.BiConsumer;
@@ -99,7 +99,7 @@ static class State<T> implements Iterable<T> {
         final Function<? super T, ?> mapper;
 
         State(boolean unique, Function<? super T, ?> mapper) {
-            this.deque = new ArrayDeque<>();
+            this.deque = new LinkedList<>();
             this.mappedElements = new HashSet<>();
             this.unique = unique;
             this.mapper = mapper;

src/test/java/io/github/jhspetersson/packrat/DropLastNTest.java

@@ -3,8 +3,10 @@
 import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.stream.IntStream;
+import java.util.stream.Stream;
 
 import static io.github.jhspetersson.packrat.TestUtils.isOrderedSequence;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -94,6 +96,15 @@ void dropLastWithStreamMuchLargerThanBuffer() {
         assertEquals(94, result.getLast());
     }
 
+    @Test
+    void dropLastWithNullElements() {
+        var after = Stream.of("a", null, "b", null, "c")
+                .gather(Packrat.dropLast(2))
+                .toList();
+
+        assertEquals(Arrays.asList("a", null, "b"), after);
+    }
+
     @Test
     void dropLastLargeNWithLargerStream() {
         var result = IntStream.range(0, 50).boxed()

src/test/java/io/github/jhspetersson/packrat/LastNTest.java

@@ -3,8 +3,10 @@
 import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.stream.IntStream;
+import java.util.stream.Stream;
 
 import static io.github.jhspetersson.packrat.TestUtils.getEmployees;
 import static io.github.jhspetersson.packrat.TestUtils.isOrderedSequence;
@@ -110,6 +112,15 @@ public void nullMapperThrows() {
         assertThrows(NullPointerException.class, () -> new LastingGatherer<Employee>(3, true, null));
     }
 
+    @Test
+    void lastWithNullElements() {
+        var after = Stream.of("a", null, "b", null, "c")
+                .gather(Packrat.last(2))
+                .toList();
+
+        assertEquals(Arrays.asList(null, "c"), after);
+    }
+
     @Test
     void lastUniqueShouldMoveDuplicateToEnd() {
         var result = List.of("A", "B", "C", "A").stream()

src/test/java/io/github/jhspetersson/packrat/WindowSlidingWithIndexTest.java

@@ -2,6 +2,7 @@
 
 import org.junit.jupiter.api.Test;
 
+import java.util.Arrays;
 import java.util.List;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
@@ -27,6 +28,19 @@ public void windowSlidingWithIndexTest() {
         assertEquals(List.of(8, 9, 10), result.get(7).getValue());
     }
 
+    @Test
+    public void windowSlidingWithIndexNullElementsTest() {
+        var result = Stream.of("a", null, "b").gather(Packrat.windowSlidingWithIndex(2)).toList();
+
+        assertEquals(2, result.size());
+
+        assertEquals(0L, result.get(0).getKey());
+        assertEquals(Arrays.asList("a", null), result.get(0).getValue());
+
+        assertEquals(1L, result.get(1).getKey());
+        assertEquals(Arrays.asList(null, "b"), result.get(1).getValue());
+    }
+
     @Test
     public void windowSlidingWithIndexCustomStartTest() {
         var numbers = IntStream.rangeClosed(1, 5).boxed();