I learned another thing about java streams today. ...
# ask-aic
charles
12/16/2020, 6:51 PM
I learned another thing about java streams today. Anyone want to guess what this code snippet prints out? I'll put the answer in the thread, so don't open the thread if you want to puzzle about it first.
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public static void main(String[] args) {
final List<Integer> integers = List.of(1, 2, 3, 4);
final long count = integers
.stream()
.peek(i -> System.out.println("i = " + i))
.count();
System.out.println("count = " + count);
}🙌 1
charles
12/16/2020, 6:51 PM
The answer is it prints just (the value stored in the count variable):
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count = 4 Copy code
i = 1
i = 2
i = 3
i = 4
count = 4charles
12/16/2020, 6:51 PM
the block in peek is never executed.
charles
12/16/2020, 6:51 PM
some explanation as to why this is the case https://stackoverflow.com/questions/59592076/intermediate-stream-operations-not-evaluated-on-count
charles
12/16/2020, 6:57 PM
and so if you have the filter in there it does print. e.g.
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public static void main(String[] args) {
final List<Integer> integers = List.of(1, 2, 3, 4);
final long count = integers
.stream()
.peek(i -> System.out.println("before filter i = " + i))
.filter(i -> i < 5)
.peek(i -> System.out.println("after filter i = " + i))
.count();
System.out.println("count = " + count);
} Copy code
before filter i = 1
after filter i = 1
before filter i = 2
after filter i = 2
before filter i = 3
after filter i = 3
before filter i = 4
after filter i = 4
count = 4m
Michel
12/16/2020, 7:55 PM
This is a confirmation that
streamsr
Roshan George
12/16/2020, 8:55 PMImagine not using
.reduce((a,b) -> a + 1)🤣 2
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