Introduction to Programming

Peeking

A Stream<T> peek(Consumer<T> action) intermediate operation applies the provided Consumer function to each stream element and does not change this Stream (returns the same element value it has received) because the Consumer function returns void and cannot affect the value. This operation is used for debugging.  

The following code shows how it works:

List<String> list = List.of("1", "2", "3", "4", "5");list.stream().peek(s-> {    if("3".equals(s)){        System.out.print(3);    }}).forEach(System.out::print);  //prints: 123345