Polishing Window scrolling API.

Moved general-purpose factory methods to the common ScrollPosition interface. Introduced a couple of domain specific methods to conveniently work with both Keyset- (to e.g. change direction) and OffsetScrollPosition (to e.g. advance the offset). Consolidated unit tests accordingly.

Moved WindowIterator to ….data.support package. Fixed case of Direction enum values.

Fixes #2824.

src/main/asciidoc/repositories-paging-sorting.adoc

@@ -14,7 +14,7 @@ Page<User> findByLastname(String lastname, Pageable pageable);
 
 Slice<User> findByLastname(String lastname, Pageable pageable);
 
-Scroll<User> findTop10ByLastname(String lastname, ScrollPosition position, Sort sort);
+Window<User> findTop10ByLastname(String lastname, ScrollPosition position, Sort sort);
 
 List<User> findByLastname(String lastname, Sort sort);
 

src/main/java/org/springframework/data/domain/KeysetScrollPosition.java

@@ -18,27 +18,33 @@ package org.springframework.data.domain;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Objects;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 
 /**
- * A {@link ScrollPosition} based on the last seen keyset. Keyset scrolling must be associated with a {@link Sort
- * well-defined sort} to be able to extract the keyset when resuming scrolling within the sorted result set.
+ * A {@link ScrollPosition} based on the last seen key set. Keyset scrolling must be associated with a {@link Sort
+ * well-defined sort} to be able to extract the key set when resuming scrolling within the sorted result set.
  *
  * @author Mark Paluch
+ * @author Oliver Drotbohm
  * @since 3.1
  */
 public final class KeysetScrollPosition implements ScrollPosition {
 
-	private static final KeysetScrollPosition initial = new KeysetScrollPosition(Collections.emptyMap(),
-			Direction.Forward);
+	private static final KeysetScrollPosition INITIAL = new KeysetScrollPosition(Collections.emptyMap(),
+			Direction.FORWARD);
 
 	private final Map<String, Object> keys;
-
 	private final Direction direction;
 
 	private KeysetScrollPosition(Map<String, Object> keys, Direction direction) {
+
+		Assert.notNull(keys, "Keys must not be null");
+		Assert.notNull(direction, "Direction must not be null");
+
 		this.keys = keys;
 		this.direction = direction;
 	}
@@ -46,44 +52,27 @@ public final class KeysetScrollPosition implements ScrollPosition {
 	/**
 	 * Creates a new initial {@link KeysetScrollPosition} to start scrolling using keyset-queries.
 	 *
-	 * @return a new initial {@link KeysetScrollPosition} to start scrolling using keyset-queries.
+	 * @return will never be {@literal null}.
 	 */
-	public static KeysetScrollPosition initial() {
-		return initial;
+	static KeysetScrollPosition initial() {
+		return INITIAL;
 	}
 
 	/**
-	 * Creates a new {@link KeysetScrollPosition} from a keyset.
-	 *
-	 * @param keys must not be {@literal null}.
-	 * @return a new {@link KeysetScrollPosition} for the given keyset.
-	 */
-	public static KeysetScrollPosition of(Map<String, ?> keys) {
-		return of(keys, Direction.Forward);
-	}
-
-	/**
-	 * Creates a new {@link KeysetScrollPosition} from a keyset and {@link Direction}.
+	 * Creates a new {@link KeysetScrollPosition} from a key set and {@link Direction}.
 	 *
 	 * @param keys must not be {@literal null}.
 	 * @param direction must not be {@literal null}.
-	 * @return a new {@link KeysetScrollPosition} for the given keyset and {@link Direction}.
+	 * @return will never be {@literal null}.
 	 */
-	public static KeysetScrollPosition of(Map<String, ?> keys, Direction direction) {
+	static KeysetScrollPosition of(Map<String, ?> keys, Direction direction) {
 
 		Assert.notNull(keys, "Keys must not be null");
 		Assert.notNull(direction, "Direction must not be null");
 
-		if (keys.isEmpty()) {
-			return initial();
-		}
-
-		return new KeysetScrollPosition(Collections.unmodifiableMap(new LinkedHashMap<>(keys)), direction);
-	}
-
-	@Override
-	public boolean isInitial() {
-		return keys.isEmpty();
+		return keys.isEmpty()
+				? initial()
+				: new KeysetScrollPosition(Collections.unmodifiableMap(new LinkedHashMap<>(keys)), direction);
 	}
 
 	/**
@@ -100,45 +89,78 @@ public final class KeysetScrollPosition implements ScrollPosition {
 		return direction;
 	}
 
+	/**
+	 * Returns whether the current {@link KeysetScrollPosition} scrolls forward.
+	 *
+	 * @return whether the current {@link KeysetScrollPosition} scrolls forward.
+	 */
+	public boolean scrollsForward() {
+		return direction == Direction.FORWARD;
+	}
+
+	/**
+	 * Returns whether the current {@link KeysetScrollPosition} scrolls backward.
+	 *
+	 * @return whether the current {@link KeysetScrollPosition} scrolls backward.
+	 */
+	public boolean scrollsBackward() {
+		return direction == Direction.BACKWARD;
+	}
+
+	/**
+	 * Returns a {@link KeysetScrollPosition} based on the same keyset and scrolling forward.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public KeysetScrollPosition forward() {
+		return direction == Direction.FORWARD ? this : new KeysetScrollPosition(keys, Direction.FORWARD);
+	}
+
+	/**
+	 * Returns a {@link KeysetScrollPosition} based on the same keyset and scrolling backward.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public KeysetScrollPosition backward() {
+		return direction == Direction.BACKWARD ? this : new KeysetScrollPosition(keys, Direction.BACKWARD);
+	}
+
+	/**
+	 * Returns a new {@link KeysetScrollPosition} with the direction reversed.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public KeysetScrollPosition reverse() {
+		return new KeysetScrollPosition(keys, direction.reverse());
+	}
+
 	@Override
-	public boolean equals(Object o) {
-		if (this == o)
+	public boolean isInitial() {
+		return keys.isEmpty();
+	}
+
+	@Override
+	public boolean equals(@Nullable Object o) {
+
+		if (this == o) {
 			return true;
-		if (o == null || getClass() != o.getClass())
+		}
+
+		if (!(o instanceof KeysetScrollPosition that)) {
 			return false;
-		KeysetScrollPosition that = (KeysetScrollPosition) o;
-		return ObjectUtils.nullSafeEquals(keys, that.keys) && direction == that.direction;
+		}
+
+		return ObjectUtils.nullSafeEquals(keys, that.keys) //
+				&& direction == that.direction;
 	}
 
 	@Override
 	public int hashCode() {
-
-		int result = 17;
-
-		result += 31 * ObjectUtils.nullSafeHashCode(keys);
-		result += 31 * ObjectUtils.nullSafeHashCode(direction);
-
-		return result;
+		return Objects.hash(keys, direction);
 	}
 
 	@Override
 	public String toString() {
 		return String.format("KeysetScrollPosition [%s, %s]", direction, keys);
 	}
-
-	/**
-	 * Keyset scrolling direction.
-	 */
-	public enum Direction {
-
-		/**
-		 * Forward (default) direction to scroll from the beginning of the results to their end.
-		 */
-		Forward,
-
-		/**
-		 * Backward direction to scroll from the end of the results to their beginning.
-		 */
-		Backward;
-	}
 }

src/main/java/org/springframework/data/domain/OffsetScrollPosition.java

@@ -15,49 +15,54 @@
  */
 package org.springframework.data.domain;
 
+import java.util.Objects;
 import java.util.function.IntFunction;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
-import org.springframework.util.ObjectUtils;
 
 /**
  * A {@link ScrollPosition} based on the offsets within query results.
  *
  * @author Mark Paluch
+ * @author Oliver Drotbohm
  * @since 3.1
  */
 public final class OffsetScrollPosition implements ScrollPosition {
 
-	private static final OffsetScrollPosition initial = new OffsetScrollPosition(0);
+	private static final OffsetScrollPosition INITIAL = new OffsetScrollPosition(0);
 
 	private final long offset;
 
+	/**
+	 * Creates a new {@link OffsetScrollPosition} for the given non-negative offset.
+	 *
+	 * @param offset must be greater or equal to zero.
+	 */
 	private OffsetScrollPosition(long offset) {
+
+		Assert.isTrue(offset >= 0, "Offset must not be negative");
+
 		this.offset = offset;
 	}
 
 	/**
 	 * Creates a new initial {@link OffsetScrollPosition} to start scrolling using offset/limit.
 	 *
-	 * @return a new initial {@link OffsetScrollPosition} to start scrolling using offset/limit.
+	 * @return will never be {@literal null}.
 	 */
-	public static OffsetScrollPosition initial() {
-		return initial;
+	static OffsetScrollPosition initial() {
+		return INITIAL;
 	}
 
 	/**
 	 * Creates a new {@link OffsetScrollPosition} from an {@code offset}.
 	 *
-	 * @param offset
-	 * @return a new {@link OffsetScrollPosition} with the given {@code offset}.
+	 * @param offset the non-negative offset to start at.
+	 * @return will never be {@literal null}.
 	 */
-	public static OffsetScrollPosition of(long offset) {
-
-		if (offset == 0) {
-			return initial();
-		}
-
-		return new OffsetScrollPosition(offset);
+	static OffsetScrollPosition of(long offset) {
+		return offset == 0 ? initial() : new OffsetScrollPosition(offset);
 	}
 
 	/**
@@ -73,36 +78,51 @@ public final class OffsetScrollPosition implements ScrollPosition {
 		return startOffset == 0 ? OffsetPositionFunction.ZERO : new OffsetPositionFunction(startOffset);
 	}
 
-	@Override
-	public boolean isInitial() {
-		return offset == 0;
-	}
-
 	/**
+	 * The zero or positive offset.
+	 *
 	 * @return the offset.
 	 */
 	public long getOffset() {
 		return offset;
 	}
 
+	/**
+	 * Returns a new {@link OffsetScrollPosition} that has been advanced by the given value. Negative deltas will be
+	 * constrained so that the new offset is at least zero.
+	 *
+	 * @param delta the value to advance the current offset by.
+	 * @return will never be {@literal null}.
+	 */
+	public OffsetScrollPosition advanceBy(long delta) {
+
+		var value = offset + delta;
+
+		return new OffsetScrollPosition(value < 0 ? 0 : value);
+	}
+
 	@Override
-	public boolean equals(Object o) {
-		if (this == o)
+	public boolean isInitial() {
+		return offset == 0;
+	}
+
+	@Override
+	public boolean equals(@Nullable Object o) {
+
+		if (this == o) {
 			return true;
-		if (o == null || getClass() != o.getClass())
+		}
+
+		if (!(o instanceof OffsetScrollPosition that)) {
 			return false;
-		OffsetScrollPosition that = (OffsetScrollPosition) o;
+		}
+
 		return offset == that.offset;
 	}
 
 	@Override
 	public int hashCode() {
-
-		int result = 17;
-
-		result += 31 * ObjectUtils.nullSafeHashCode(offset);
-
-		return result;
+		return Objects.hash(offset);
 	}
 
 	@Override

src/main/java/org/springframework/data/domain/Pageable.java

@@ -174,7 +174,6 @@ public interface Pageable {
 			throw new IllegalStateException("Cannot create OffsetScrollPosition from an unpaged instance");
 		}
 
-		return OffsetScrollPosition.of(getOffset());
+		return ScrollPosition.offset(getOffset());
 	}
-
 }

src/main/java/org/springframework/data/domain/ScrollPosition.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.domain;
 
+import java.util.Map;
+
 /**
  * Interface to specify a position within a total query result. Scroll positions are used to start scrolling from the
  * beginning of a query result or to resume scrolling from a given position within the query result.
@@ -30,4 +32,83 @@ public interface ScrollPosition {
 	 * @return
 	 */
 	boolean isInitial();
+
+	/**
+	 * Creates a new initial {@link ScrollPosition} to start scrolling using keyset-queries.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public static KeysetScrollPosition keyset() {
+		return KeysetScrollPosition.initial();
+	}
+
+	/**
+	 * Creates a new initial {@link ScrollPosition} to start scrolling using offset / limit.
+	 *
+	 * @return will never be {@literal null}.
+	 */
+	public static OffsetScrollPosition offset() {
+		return OffsetScrollPosition.initial();
+	}
+
+	/**
+	 * Creates a new {@link ScrollPosition} from an {@code offset}.
+	 *
+	 * @param offset
+	 * @return a new {@link OffsetScrollPosition} with the given {@code offset}.
+	 */
+	public static OffsetScrollPosition offset(long offset) {
+		return OffsetScrollPosition.of(offset);
+	}
+
+	/**
+	 * Creates a new {@link ScrollPosition} from a key set scrolling forward.
+	 *
+	 * @param keys must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	public static KeysetScrollPosition forward(Map<String, ?> keys) {
+		return of(keys, Direction.FORWARD);
+	}
+
+	/**
+	 * Creates a new {@link ScrollPosition} from a key set scrolling backward.
+	 *
+	 * @param keys must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	public static KeysetScrollPosition backward(Map<String, ?> keys) {
+		return of(keys, Direction.BACKWARD);
+	}
+
+	/**
+	 * Creates a new {@link ScrollPosition} from a key set and {@link Direction}.
+	 *
+	 * @param keys must not be {@literal null}.
+	 * @param direction must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 */
+	public static KeysetScrollPosition of(Map<String, ?> keys, Direction direction) {
+		return KeysetScrollPosition.of(keys, direction);
+	}
+
+	/**
+	 * Keyset scrolling direction.
+	 */
+	public enum Direction {
+
+		/**
+		 * Forward (default) direction to scroll from the beginning of the results to their end.
+		 */
+		FORWARD,
+
+		/**
+		 * Backward direction to scroll from the end of the results to their beginning.
+		 */
+		BACKWARD;
+
+		Direction reverse() {
+			return this == FORWARD ? BACKWARD : FORWARD;
+		}
+	}
 }

src/main/java/org/springframework/data/support/WindowIterator.java

@@ -13,12 +13,14 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.data.domain;
+package org.springframework.data.support;
 
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 import java.util.function.Function;
 
+import org.springframework.data.domain.ScrollPosition;
+import org.springframework.data.domain.Window;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -28,7 +30,7 @@ import org.springframework.util.Assert;
  *
  * <pre class="code">
  * WindowIterator&lt;User&gt; users = WindowIterator.of(position -> repository.findFirst10By…("spring", position))
- *   .startingAt(OffsetScrollPosition.initial());
+ *   .startingAt(ScrollPosition.offset());
  *
  * while (users.hasNext()) {
  *   User u = users.next();

src/test/java/org/springframework/data/domain/KeysetScrollPositionUnitTests.java

@@ -1,43 +0,0 @@
-/*
- * Copyright 2023 the original author or authors.
- *
- * 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
- *
- *      https://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 org.springframework.data.domain;
-
-import static org.assertj.core.api.Assertions.*;
-
-import java.util.Collections;
-
-import org.junit.jupiter.api.Test;
-import org.springframework.data.domain.KeysetScrollPosition.Direction;
-
-/**
- * Unit tests for {@link KeysetScrollPosition}.
- *
- * @author Mark Paluch
- */
-class KeysetScrollPositionUnitTests {
-
-	@Test // GH-2151
-	void equalsAndHashCode() {
-
-		KeysetScrollPosition foo1 = KeysetScrollPosition.of(Collections.singletonMap("k", "v"));
-		KeysetScrollPosition foo2 = KeysetScrollPosition.of(Collections.singletonMap("k", "v"));
-		KeysetScrollPosition bar = KeysetScrollPosition.of(Collections.singletonMap("k", "v"), Direction.Backward);
-
-		assertThat(foo1).isEqualTo(foo2).hasSameClassAs(foo2);
-		assertThat(foo1).isNotEqualTo(bar).doesNotHaveSameHashCodeAs(bar);
-	}
-
-}

src/test/java/org/springframework/data/domain/OffsetScrollPositionUnitTests.java

@@ -1,50 +0,0 @@
-/*
- * Copyright 2023 the original author or authors.
- *
- * 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
- *
- *      https://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 org.springframework.data.domain;
-
-import static org.assertj.core.api.Assertions.*;
-import static org.springframework.data.domain.OffsetScrollPosition.*;
-
-import org.junit.jupiter.api.Test;
-
-/**
- * Unit tests for {@link OffsetScrollPosition}.
- *
- * @author Mark Paluch
- */
-class OffsetScrollPositionUnitTests {
-
-	@Test // GH-2151
-	void equalsAndHashCode() {
-
-		OffsetScrollPosition foo1 = OffsetScrollPosition.of(1);
-		OffsetScrollPosition foo2 = OffsetScrollPosition.of(1);
-		OffsetScrollPosition bar = OffsetScrollPosition.of(2);
-
-		assertThat(foo1).isEqualTo(foo2).hasSameClassAs(foo2);
-		assertThat(foo1).isNotEqualTo(bar).doesNotHaveSameHashCodeAs(bar);
-	}
-
-	@Test // GH-2151
-	void shouldCreateCorrectIndexPosition() {
-
-		assertThat(positionFunction(0).apply(0)).isEqualTo(OffsetScrollPosition.of(1));
-		assertThat(positionFunction(0).apply(1)).isEqualTo(OffsetScrollPosition.of(2));
-
-		assertThat(positionFunction(100).apply(0)).isEqualTo(OffsetScrollPosition.of(101));
-		assertThat(positionFunction(100).apply(1)).isEqualTo(OffsetScrollPosition.of(102));
-	}
-}

src/test/java/org/springframework/data/domain/PageRequestUnitTests.java

@@ -72,6 +72,6 @@ class PageRequestUnitTests extends AbstractPageRequestUnitTests {
 
 		PageRequest request = PageRequest.of(1, 10);
 
-		assertThat(request.toScrollPosition()).isEqualTo(OffsetScrollPosition.of(10));
+		assertThat(request.toScrollPosition()).isEqualTo(ScrollPosition.offset(10));
 	}
 }

src/test/java/org/springframework/data/domain/ScrollPositionUnitTests.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 org.springframework.data.domain;
+
+import static org.assertj.core.api.Assertions.*;
+import static org.springframework.data.domain.OffsetScrollPosition.*;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.data.domain.ScrollPosition.Direction;
+
+/**
+ * Unit tests for {@link KeysetScrollPosition}.
+ *
+ * @author Mark Paluch
+ * @author Oliver Drotbohm
+ */
+class ScrollPositionUnitTests {
+
+	private static final Map<String, ?> KEYS = Collections.singletonMap("k", "v");
+
+	@Test // GH-2151
+	void equalsAndHashCodeForKeysets() {
+
+		ScrollPosition foo1 = ScrollPosition.forward(KEYS);
+		ScrollPosition foo2 = ScrollPosition.forward(KEYS);
+		ScrollPosition bar = ScrollPosition.backward(KEYS);
+
+		assertThat(foo1).isEqualTo(foo2).hasSameClassAs(foo2);
+		assertThat(foo1).isNotEqualTo(bar).doesNotHaveSameHashCodeAs(bar);
+	}
+
+	@Test // GH-2151
+	void equalsAndHashCodeForOffsets() {
+
+		ScrollPosition foo1 = ScrollPosition.offset(1);
+		ScrollPosition foo2 = ScrollPosition.offset(1);
+		ScrollPosition bar = ScrollPosition.offset(2);
+
+		assertThat(foo1).isEqualTo(foo2).hasSameClassAs(foo2);
+		assertThat(foo1).isNotEqualTo(bar).doesNotHaveSameHashCodeAs(bar);
+	}
+
+	@Test // GH-2151
+	void shouldCreateCorrectIndexPosition() {
+
+		assertThat(positionFunction(0).apply(0)).isEqualTo(ScrollPosition.offset(1));
+		assertThat(positionFunction(0).apply(1)).isEqualTo(ScrollPosition.offset(2));
+
+		assertThat(positionFunction(100).apply(0)).isEqualTo(ScrollPosition.offset(101));
+		assertThat(positionFunction(100).apply(1)).isEqualTo(ScrollPosition.offset(102));
+	}
+
+	@Test // GH-2151
+	void rejectsNegativeOffset() {
+		assertThatIllegalArgumentException().isThrownBy(() -> ScrollPosition.offset(-1));
+	}
+
+	@Test // GH-2151
+	void advanceOffsetBelowZeroCapsAtZero() {
+
+		OffsetScrollPosition offset = ScrollPosition.offset(5);
+
+		assertThat(offset.getOffset()).isEqualTo(5);
+		assertThat(offset.advanceBy(-10)).isEqualTo(ScrollPosition.offset(0));
+	}
+
+	@Test // GH-2824
+	void setsUpForwardScrolling() {
+
+		KeysetScrollPosition position = ScrollPosition.forward(KEYS);
+
+		assertThat(position.getKeys()).isEqualTo(KEYS);
+		assertThat(position.getDirection()).isEqualTo(Direction.FORWARD);
+		assertThat(position.scrollsForward()).isTrue();
+		assertThat(position.scrollsBackward()).isFalse();
+
+		KeysetScrollPosition backward = position.backward();
+
+		assertThat(backward.getKeys()).isEqualTo(KEYS);
+		assertThat(backward.getDirection()).isEqualTo(Direction.BACKWARD);
+		assertThat(backward.scrollsForward()).isFalse();
+		assertThat(backward.scrollsBackward()).isTrue();
+
+		assertThat(position.reverse()).isEqualTo(backward);
+	}
+
+	@Test // GH-2824
+	void setsUpBackwardScrolling() {
+
+		KeysetScrollPosition position = ScrollPosition.backward(KEYS);
+
+		assertThat(position.getKeys()).isEqualTo(KEYS);
+		assertThat(position.getDirection()).isEqualTo(Direction.BACKWARD);
+		assertThat(position.scrollsForward()).isFalse();
+		assertThat(position.scrollsBackward()).isTrue();
+
+		KeysetScrollPosition forward = position.forward();
+
+		assertThat(forward.getKeys()).isEqualTo(KEYS);
+		assertThat(forward.getDirection()).isEqualTo(Direction.FORWARD);
+		assertThat(forward.scrollsForward()).isTrue();
+		assertThat(forward.scrollsBackward()).isFalse();
+
+		assertThat(position.reverse()).isEqualTo(forward);
+	}
+
+	@Test // GH-2824
+	void initialOffsetPosition() {
+
+		OffsetScrollPosition position = ScrollPosition.offset();
+
+		assertThat(position.isInitial()).isTrue();
+		assertThat(position.getOffset()).isEqualTo(0);
+	}
+
+	@Test // GH-2824
+	void initialKeysetPosition() {
+
+		KeysetScrollPosition keyset = ScrollPosition.keyset();
+
+		assertThat(keyset.isInitial()).isTrue();
+		assertThat(keyset.scrollsForward()).isTrue();
+	}
+}

src/test/java/org/springframework/data/domain/WindowIteratorUnitTests.java

@@ -30,6 +30,7 @@ import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.junit.jupiter.MockitoExtension;
 import org.mockito.junit.jupiter.MockitoSettings;
 import org.mockito.quality.Strictness;
+import org.springframework.data.support.WindowIterator;
 
 /**
  * Unit tests for {@link WindowIterator}.
@@ -45,20 +46,20 @@ class WindowIteratorUnitTests {
 	void loadsDataOnNext() {
 
 		Function<ScrollPosition, Window<String>> fkt = mock(Function.class);
-		WindowIterator<String> iterator = WindowIterator.of(fkt).startingAt(OffsetScrollPosition.initial());
+		WindowIterator<String> iterator = WindowIterator.of(fkt).startingAt(ScrollPosition.offset());
 		verifyNoInteractions(fkt);
 
-		when(fkt.apply(any())).thenReturn(Window.from(Collections.emptyList(), value -> OffsetScrollPosition.initial()));
+		when(fkt.apply(any())).thenReturn(Window.from(Collections.emptyList(), value -> ScrollPosition.offset()));
 
 		iterator.hasNext();
-		verify(fkt).apply(OffsetScrollPosition.initial());
+		verify(fkt).apply(ScrollPosition.offset());
 	}
 
 	@Test // GH-2151
 	void hasNextReturnsFalseIfNoDataAvailable() {
 
-		Window<Object> window = Window.from(Collections.emptyList(), value -> OffsetScrollPosition.initial());
-		WindowIterator<Object> iterator = WindowIterator.of(it -> window).startingAt(OffsetScrollPosition.initial());
+		Window<Object> window = Window.from(Collections.emptyList(), value -> ScrollPosition.offset());
+		WindowIterator<Object> iterator = WindowIterator.of(it -> window).startingAt(ScrollPosition.offset());
 
 		assertThat(iterator.hasNext()).isFalse();
 	}
@@ -66,8 +67,8 @@ class WindowIteratorUnitTests {
 	@Test // GH-2151
 	void nextThrowsExceptionIfNoElementAvailable() {
 
-		Window<Object> window = Window.from(Collections.emptyList(), value -> OffsetScrollPosition.initial());
-		WindowIterator<Object> iterator = WindowIterator.of(it -> window).startingAt(OffsetScrollPosition.initial());
+		Window<Object> window = Window.from(Collections.emptyList(), value -> ScrollPosition.offset());
+		WindowIterator<Object> iterator = WindowIterator.of(it -> window).startingAt(ScrollPosition.offset());
 
 		assertThatExceptionOfType(NoSuchElementException.class).isThrownBy(iterator::next);
 	}
@@ -75,8 +76,8 @@ class WindowIteratorUnitTests {
 	@Test // GH-2151
 	void hasNextReturnsTrueIfDataAvailableButOnlyOnePage() {
 
-		Window<String> window = Window.from(List.of("a", "b"), value -> OffsetScrollPosition.initial());
-		WindowIterator<String> iterator = WindowIterator.of(it -> window).startingAt(OffsetScrollPosition.initial());
+		Window<String> window = Window.from(List.of("a", "b"), value -> ScrollPosition.offset());
+		WindowIterator<String> iterator = WindowIterator.of(it -> window).startingAt(ScrollPosition.offset());
 
 		assertThat(iterator.hasNext()).isTrue();
 		assertThat(iterator.next()).isEqualTo("a");
@@ -89,14 +90,14 @@ class WindowIteratorUnitTests {
 	@Test // GH-2151
 	void hasNextReturnsCorrectlyIfNextPageIsEmpty() {
 
-		Window<String> window = Window.from(List.of("a", "b"), value -> OffsetScrollPosition.initial());
+		Window<String> window = Window.from(List.of("a", "b"), value -> ScrollPosition.offset());
 		WindowIterator<String> iterator = WindowIterator.of(it -> {
 			if (it.isInitial()) {
 				return window;
 			}
 
 			return Window.from(Collections.emptyList(), OffsetScrollPosition::of, false);
-		}).startingAt(OffsetScrollPosition.initial());
+		}).startingAt(ScrollPosition.offset());
 
 		assertThat(iterator.hasNext()).isTrue();
 		assertThat(iterator.next()).isEqualTo("a");
@@ -109,15 +110,15 @@ class WindowIteratorUnitTests {
 	@Test // GH-2151
 	void allowsToIterateAllWindows() {
 
-		Window<String> window1 = Window.from(List.of("a", "b"), OffsetScrollPosition::of, true);
-		Window<String> window2 = Window.from(List.of("c", "d"), value -> OffsetScrollPosition.of(2 + value));
+		Window<String> window1 = Window.from(List.of("a", "b"), ScrollPosition::offset, true);
+		Window<String> window2 = Window.from(List.of("c", "d"), value -> ScrollPosition.offset(2 + value));
 		WindowIterator<String> iterator = WindowIterator.of(it -> {
 			if (it.isInitial()) {
 				return window1;
 			}
 
 			return window2;
-		}).startingAt(OffsetScrollPosition.initial());
+		}).startingAt(ScrollPosition.offset());
 
 		List<String> capturedResult = new ArrayList<>(4);
 		while (iterator.hasNext()) {

src/test/java/org/springframework/data/domain/WindowUnitTests.java

@@ -58,13 +58,13 @@ class WindowUnitTests {
 
 		Window<Integer> window = Window.from(List.of(1, 2, 3), OffsetScrollPosition.positionFunction(0));
 
-		assertThat(window.positionAt(0)).isEqualTo(OffsetScrollPosition.of(1));
-		assertThat(window.positionAt(window.size() - 1)).isEqualTo(OffsetScrollPosition.of(3));
+		assertThat(window.positionAt(0)).isEqualTo(ScrollPosition.offset(1));
+		assertThat(window.positionAt(window.size() - 1)).isEqualTo(ScrollPosition.offset(3));
 
 		// by index
-		assertThat(window.positionAt(1)).isEqualTo(OffsetScrollPosition.of(2));
+		assertThat(window.positionAt(1)).isEqualTo(ScrollPosition.offset(2));
 
 		// by object
-		assertThat(window.positionAt(Integer.valueOf(1))).isEqualTo(OffsetScrollPosition.of(1));
+		assertThat(window.positionAt(Integer.valueOf(1))).isEqualTo(ScrollPosition.offset(1));
 	}
 }

src/test/java/org/springframework/data/repository/query/ParametersParameterAccessorUnitTests.java

@@ -19,7 +19,6 @@ import static org.assertj.core.api.Assertions.*;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import org.springframework.data.domain.OffsetScrollPosition;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.ScrollPosition;
@@ -84,7 +83,7 @@ class ParametersParameterAccessorUnitTests {
 		var method = Sample.class.getMethod("method", ScrollPosition.class, String.class);
 		var parameters = new DefaultParameters(method);
 
-		var accessor = new ParametersParameterAccessor(parameters, new Object[] { OffsetScrollPosition.of(1), "Foo" });
+		var accessor = new ParametersParameterAccessor(parameters, new Object[] { ScrollPosition.offset(1), "Foo" });
 
 		assertThat(accessor).hasSize(1);
 		assertThat(accessor.getBindableValue(0)).isEqualTo("Foo");

src/test/java/org/springframework/data/repository/query/SimpleParameterAccessorUnitTests.java

@@ -19,7 +19,6 @@ import static org.assertj.core.api.Assertions.*;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import org.springframework.data.domain.OffsetScrollPosition;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.ScrollPosition;
@@ -61,7 +60,8 @@ class SimpleParameterAccessorUnitTests {
 
 	@Test
 	void rejectsTooLittleNumberOfArguments() {
-		assertThatIllegalArgumentException().isThrownBy(() -> new ParametersParameterAccessor(parameters, new Object[0]));
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> new ParametersParameterAccessor(parameters, new Object[0]));
 	}
 
 	@Test
@@ -82,7 +82,7 @@ class SimpleParameterAccessorUnitTests {
 	@Test // GH-2151
 	void returnsScrollPositionIfAvailable() {
 
-		var cursorRequest = OffsetScrollPosition.of(1);
+		var cursorRequest = ScrollPosition.offset(1);
 		ParameterAccessor accessor = new ParametersParameterAccessor(cursorRequestParameters,
 				new Object[] { cursorRequest });
 
@@ -103,7 +103,8 @@ class SimpleParameterAccessorUnitTests {
 	void returnsPageableIfAvailable() {
 
 		Pageable pageable = PageRequest.of(0, 10);
-		ParameterAccessor accessor = new ParametersParameterAccessor(pageableParameters, new Object[] { "test", pageable });
+		ParameterAccessor accessor = new ParametersParameterAccessor(pageableParameters,
+				new Object[] { "test", pageable });
 
 		assertThat(accessor.getPageable()).isEqualTo(pageable);
 		assertThat(accessor.getSort().isSorted()).isFalse();
@@ -114,7 +115,8 @@ class SimpleParameterAccessorUnitTests {
 
 		var sort = Sort.by("foo");
 		Pageable pageable = PageRequest.of(0, 10, sort);
-		ParameterAccessor accessor = new ParametersParameterAccessor(pageableParameters, new Object[] { "test", pageable });
+		ParameterAccessor accessor = new ParametersParameterAccessor(pageableParameters,
+				new Object[] { "test", pageable });
 
 		assertThat(accessor.getPageable()).isEqualTo(pageable);
 		assertThat(accessor.getSort()).isEqualTo(sort);