...

public final class SlidingWindows {
   
	 /**
     * Return a window definition with the given window size and given window grace period
     * Records that come after set grace period will be ignored
     *
     * @param size, The size of the window
     * @param grace, The grace period to admit out-of-order events to a window
     * @return a new window definition
     * @throws IllegalArgumentException if the specified window size or grace is zero or negative or can't be represented as {@code long milliseconds}
     */
	public static SlidingWindows of(final Duration size, final Duration grace) throws IllegalArgumentException{}

Addition Add additional windowedBy method to KGroupedStream.java

/**
     * Create a new {@link TimeWindowedKStream} instance that can be used to perform session windowed aggregations.
     * @param windows the specification of the aggregation {@link SlidingWindows}
     * @return an instance of {@link TimeWindowedKStream}
     */
    TimeWindowedKStream<K, V> windowedBy(final SlidingWindows windows);

Add additional windowedBy method to CogroupedKStream.java

/**
* Create a new {@link TimeWindowedCogroupedKStream} instance that can be used to perform windowed
* aggregations.
*
* @param windows the specification of the aggregation {@link SlidingWindows}
* @return an instance of {@link TimeWindowedCogroupedKStream}
*/
<W extends Window> TimeWindowedCogroupedKStream<K, VOut> windowedBy(final SlidingWindows windows);

Proposed Changes

Creating a new finals class SlidingWindows, to add aggregation flexibility and features for users. Sliding windows will have an inclusive start and end point and each window will be unique, meaning that each distinct set of records will only appear in one window. This is in contrast with hopping windows, which can mimic sliding windows with an advance of 1ms, but result in many overlapping windows, as shown below. This causes expensive aggregation calculations for each window, whereas for the sliding windows, aggregations are only done for each unique window, cutting down significantly on the amount of work required.

...