Feature/misc fixes (#191)

* Minor fixes and refactorings
* Minor fixes around JSpecify annotations

Author: tginsberg

src/main/java/com/ginsberg/gatherers4j/AccumulatingGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -66,7 +66,7 @@ public BiConsumer<State<OUTPUT>, Downstream<? super OUTPUT>> finisher() {
         };
     }
 
-    public static class State<OUTPUT> {
+    public static class State<OUTPUT extends @Nullable Object> {
         @Nullable
         OUTPUT carriedValue;
         int index;

src/main/java/com/ginsberg/gatherers4j/BigDecimalExponentialMovingAverageGatherer.java

@@ -1,3 +1,19 @@
+/*
+ * Copyright 2024-2026 Todd Ginsberg
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package com.ginsberg.gatherers4j;
 
 import org.jspecify.annotations.Nullable;

src/main/java/com/ginsberg/gatherers4j/BigDecimalSimpleMovingAverageGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -60,8 +60,8 @@ static class State implements BigDecimalGatherer.State {
         final boolean includePartialValues;
         final BigDecimal[] series;
         BigDecimal sum = BigDecimal.ZERO;
-        BigDecimal count = BigDecimal.ZERO;
         BigDecimal average = BigDecimal.ZERO;
+        int count = 0;
         int index = 0;
 
         private State(final int lookBack, final boolean includePartialValues) {
@@ -72,18 +72,18 @@ private State(final int lookBack, final boolean includePartialValues) {
 
         @Override
         public boolean canCalculate() {
-            return includePartialValues || count.intValue() >= series.length;
+            return includePartialValues || count >= series.length;
         }
 
         @Override
         public void add(final BigDecimal element, final MathContext mathContext) {
             sum = sum.subtract(series[index]).add(element, mathContext);
             series[index % series.length] = element;
             index = (index + 1) % series.length;
-            if (count.intValue() < series.length) {
-                count = count.add(BigDecimal.ONE);
+            if (count < series.length) {
+                count++;
             }
-            average = sum.divide(count, mathContext);
+            average = sum.divide(BigDecimal.valueOf(count), mathContext);
         }
 
         @Override

src/main/java/com/ginsberg/gatherers4j/DistinctGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,7 +29,7 @@
 public class DistinctGatherer<INPUT extends @Nullable Object>
         implements Gatherer<INPUT, DistinctGatherer.State, INPUT> {
 
-    private final Function<INPUT, Object> mappingFunction;
+    private final Function<INPUT, @Nullable Object> mappingFunction;
 
     DistinctGatherer(final Function<INPUT, @Nullable Object> mappingFunction) {
         this.mappingFunction = mustNotBeNull(mappingFunction, "Mapping function must not be null");

src/main/java/com/ginsberg/gatherers4j/FilterChangingGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,7 @@
 
 import static com.ginsberg.gatherers4j.util.GathererUtils.mustNotBeNull;
 
-public class FilterChangingGatherer<INPUT>
+public class FilterChangingGatherer<INPUT extends @Nullable Object>
         implements Gatherer<INPUT, FilterChangingGatherer.State<INPUT>, INPUT> {
 
     private final Order operation;
@@ -76,7 +76,7 @@ boolean allow(final @Nullable INPUT previous, final INPUT next) {
         return operation.allows(comparator.compare(next, previous));
     }
 
-    public static class State<INPUT> {
+    public static class State<INPUT extends @Nullable Object> {
         boolean first = true;
         @Nullable
         INPUT previousElement;

src/main/java/com/ginsberg/gatherers4j/FrequencyGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -66,7 +66,8 @@ public BiConsumer<State<INPUT>, Downstream<? super WithCount<INPUT>>> finisher()
         return (inputState, downstream) -> {
             var counts = inputState.counts
                     .entrySet()
-                    .stream().map(it -> new WithCount<>(it.getKey(), it.getValue()))
+                    .stream()
+                    .map(it -> new WithCount<INPUT>(it.getKey(), it.getValue()))
                     .sorted(comparator());
             pushAll(counts, downstream);
         };
@@ -81,7 +82,7 @@ private Comparator<WithCount<INPUT>> comparator() {
         }
     }
 
-    public static class State<INPUT> {
+    public static class State<INPUT extends @Nullable Object> {
         final Map<INPUT, Long> counts = new HashMap<>();
     }
 }

src/main/java/com/ginsberg/gatherers4j/Gatherers4j.java

@@ -278,7 +278,7 @@ private Gatherers4j() {
     /// @param validTypes A non-empty array of types to filter for
     /// @return A non-null `Gatherer`
     @SafeVarargs
-    public static <INPUT extends @Nullable Object, OUTPUT extends @Nullable Object> Gatherer<INPUT, ?, OUTPUT> filterInstanceOf(
+    public static <INPUT extends @Nullable Object, OUTPUT> Gatherer<INPUT, ?, OUTPUT> filterInstanceOf(
             final Class<? extends OUTPUT>... validTypes
     ) {
         return TypeFilteringGatherer.of(validTypes);

src/main/java/com/ginsberg/gatherers4j/GroupChangingGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package com.ginsberg.gatherers4j;
 
 import com.ginsberg.gatherers4j.enums.Order;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -28,13 +29,13 @@
 
 import static com.ginsberg.gatherers4j.util.GathererUtils.mustNotBeNull;
 
-public class GroupChangingGatherer<INPUT>
+public class GroupChangingGatherer<INPUT extends @Nullable Object>
         implements Gatherer<INPUT, GroupChangingGatherer.State<INPUT>, List<INPUT>> {
 
     private final Order operation;
     private final Comparator<INPUT> comparator;
 
-    static <INPUT> GroupChangingGatherer<INPUT> usingComparator(
+    static <INPUT extends @Nullable Object> GroupChangingGatherer<INPUT> usingComparator(
             final Order operation,
             final Comparator<INPUT> comparator
     ) {
@@ -85,7 +86,7 @@ public BiConsumer<State<INPUT>, Downstream<? super List<INPUT>>> finisher() {
         };
     }
 
-    public static class State<INPUT> {
+    public static class State<INPUT extends @Nullable Object> {
         List<INPUT> currentElements = new ArrayList<>();
     }
 

src/main/java/com/ginsberg/gatherers4j/MinMaxGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,14 +34,14 @@ public class MinMaxGatherer<INPUT extends @Nullable Object>
     private final int windowSize;
     private boolean excludePartialValues;
 
-    static <INPUT> MinMaxGatherer<INPUT> runningUsingComparator(
+    static <INPUT extends @Nullable Object> MinMaxGatherer<INPUT> runningUsingComparator(
             final boolean sortingMin,
             final Comparator<INPUT> comparator
     ) {
         return new MinMaxGatherer<>(sortingMin ? comparator : comparator.reversed());
     }
 
-    static <INPUT> MinMaxGatherer<INPUT> movingUsingComparator(
+    static <INPUT extends @Nullable Object> MinMaxGatherer<INPUT> movingUsingComparator(
             final int windowSize,
             final boolean sortingMin,
             final Comparator<INPUT> comparator
@@ -134,8 +134,8 @@ boolean eval(final INPUT nextValue) {
         }
     }
 
-    public static class MovingState<INPUT> extends State<INPUT> {
-        private record IndexValue<INPUT>(int index, INPUT value) {
+    public static class MovingState<INPUT extends @Nullable Object> extends State<INPUT> {
+        private record IndexValue<INPUT extends @Nullable Object>(int index, INPUT value) {
         }
 
         private final List<IndexValue<INPUT>> queue = new ArrayList<>();

src/main/java/com/ginsberg/gatherers4j/RepeatingGatherer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 Todd Ginsberg
+ * Copyright 2024-2026 Todd Ginsberg
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -55,8 +55,10 @@ public Supplier<RepeatingGatherer.State<INPUT>> initializer() {
     @Override
     public Integrator<RepeatingGatherer.State<INPUT>, INPUT, INPUT> integrator() {
         return Integrator.ofGreedy((state, element, downstream) -> {
-            state.theStream.add(element);
-            return repeats != 0 && !downstream.isRejecting();
+            if(repeats != 0) {
+                state.theStream.add(element);
+            }
+            return !downstream.isRejecting();
         });
     }
 
@@ -73,7 +75,7 @@ public BiConsumer<RepeatingGatherer.State<INPUT>, Downstream<? super INPUT>> fin
         };
     }
 
-    public static class State<INPUT> {
+    public static class State<INPUT extends @Nullable Object> {
         int repeatsRemaining;
         final List<INPUT> theStream = new ArrayList<>();