Stream sources, including infinite ones
The three-argument Stream.iterate and Stream.ofNullable arrived in Java 9; toList() in Java 16.
A stream is a pipeline that pulls elements from a source, passes them through intermediate operations like filter and map, and produces a result with one terminal operation. Streams are lazy (nothing runs until the terminal operation), can be used only once, and never change their source.
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Practice questions
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From List.of("tea", "coffee", "juice", "milk"), print a list of the words with more than 3 letters, upper-cased, using a stream.
Print the sum of squares of the odd numbers from 1 to 9 with a single IntStream pipeline.
Use Stream.iterate with three arguments to print the powers of 2 below 1000 as a list.
Explain it without notes
What is a stream, and how is it different from a collection?
Explain laziness in streams. What actually happens when you call filter and when you call toList?
Why can a stream be used only once?
Why do primitive streams exist, and how do you move between Stream<T> and IntStream?
Expected output
Stream.of: [a, b, c]
Arrays.stream: 6
range(0, 5): [0, 1, 2, 3, 4]
rangeClosed: 15
iterate+limit: [1, 2, 4, 8, 16, 32]
iterate, 3 arg: [1, 3, 9, 27, 81]
generate+limit: [hi, hi, hi]
String.chars: [1, 2, 3]
map entries: rice, tea
ofNullable: 0
empty: false