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counting: https://stackabuse.com/guide-to-java-8-collectors-counting/ Guide to Java 8 Collectors: counting() In this guide, learn how to count the number of elements in a collection or stream in Java, as well as how to use the Collectors.counting() as a downstream function of other collectors, with examples. stackabuse.com mapping: https://www.javabrahman.com/java-8/java-8-how-to-use-collectors-..