docs(core): fix javadoc in WindowBound

core/src/main/java/io/substrait/expression/WindowBound.java

@@ -2,28 +2,85 @@
 
 import org.immutables.value.Value;
 
+/**
+ * A bound of a window frame, such as a number of rows preceding/following, current row or
+ * unbounded.
+ */
 @Value.Enclosing
 public interface WindowBound {
 
+  /** Shared instance representing the current row bound. */
   CurrentRow CURRENT_ROW = ImmutableWindowBound.CurrentRow.builder().build();
+
+  /** Shared instance representing an unbounded frame bound. */
   Unbounded UNBOUNDED = ImmutableWindowBound.Unbounded.builder().build();
 
+  /**
+   * Visitor over the concrete {@link WindowBound} kinds.
+   *
+   * @param <R> the return type
+   * @param <E> the exception type that may be thrown
+   */
   interface WindowBoundVisitor<R, E extends Throwable> {
+    /**
+     * Visits a {@link Preceding} bound.
+     *
+     * @param preceding the preceding bound
+     * @return the result of the visit
+     */
     R visit(Preceding preceding);
 
+    /**
+     * Visits a {@link Following} bound.
+     *
+     * @param following the following bound
+     * @return the result of the visit
+     */
     R visit(Following following);
 
+    /**
+     * Visits a {@link CurrentRow} bound.
+     *
+     * @param currentRow the current-row bound
+     * @return the result of the visit
+     */
     R visit(CurrentRow currentRow);
 
+    /**
+     * Visits an {@link Unbounded} bound.
+     *
+     * @param unbounded the unbounded bound
+     * @return the result of the visit
+     */
     R visit(Unbounded unbounded);
   }
 
+  /**
+   * Accepts a visitor for this window bound.
+   *
+   * @param <R> the return type
+   * @param <E> the exception type that may be thrown
+   * @param visitor the visitor
+   * @return the result of the visit
+   */
   <R, E extends Throwable> R accept(WindowBoundVisitor<R, E> visitor);
 
+  /** A bound a fixed number of rows before the current row. */
   @Value.Immutable
   abstract class Preceding implements WindowBound {
+    /**
+     * Returns the number of rows preceding the current row.
+     *
+     * @return the offset
+     */
     public abstract long offset();
 
+    /**
+     * Creates a {@link Preceding} bound with the given offset.
+     *
+     * @param offset the number of rows preceding the current row
+     * @return the preceding bound
+     */
     public static Preceding of(long offset) {
       return ImmutableWindowBound.Preceding.builder().offset(offset).build();
     }
@@ -34,10 +91,22 @@ public <R, E extends Throwable> R accept(WindowBoundVisitor<R, E> visitor) {
     }
   }
 
+  /** A bound a fixed number of rows after the current row. */
   @Value.Immutable
   abstract class Following implements WindowBound {
+    /**
+     * Returns the number of rows following the current row.
+     *
+     * @return the offset
+     */
     public abstract long offset();
 
+    /**
+     * Creates a {@link Following} bound with the given offset.
+     *
+     * @param offset the number of rows following the current row
+     * @return the following bound
+     */
     public static Following of(long offset) {
       return ImmutableWindowBound.Following.builder().offset(offset).build();
     }
@@ -48,6 +117,7 @@ public <R, E extends Throwable> R accept(WindowBoundVisitor<R, E> visitor) {
     }
   }
 
+  /** The bound at the current row. */
   @Value.Immutable
   abstract class CurrentRow implements WindowBound {
     @Override
@@ -56,6 +126,7 @@ public <R, E extends Throwable> R accept(WindowBoundVisitor<R, E> visitor) {
     }
   }
 
+  /** An unbounded frame bound (the start or end of the partition). */
   @Value.Immutable
   abstract class Unbounded implements WindowBound {
     @Override