How to check if all elements match a condition

Short answer

allMatch() returns true if the condition holds for every element:

void main() {
    var ages = List.of(21, 34, 19);
 
    IO.println(ages.stream().allMatch(age -> age >= 18));
    IO.println(ages.stream().allMatch(age -> age >= 20));
}

Output:

true
false

At least one and none

anyMatch() checks that at least one element matches, noneMatch() that none do:

void main() {
    var passwords = List.of("secret1", "qwerty", "Tr0ub4dor");
 
    IO.println(passwords.stream().anyMatch(p -> p.length() > 8));
    IO.println(passwords.stream().noneMatch(String::isBlank));
}

Output:

true
true

Stopping at the first answer

These methods stop checking as soon as the answer is known:

void main() {
    boolean result = Stream.of(1, 2, 3, 4)
            .peek(n -> IO.println("checking " + n))
            .allMatch(n -> n < 2);
    IO.println(result);
}

Output:

checking 1
checking 2
false

Common mistake

Forgetting about an empty list. allMatch() returns true for an empty stream, and anyMatch() returns false:

void main() {
    List<Integer> empty = List.of();
 
    IO.println(empty.stream().allMatch(n -> n > 100));
    IO.println(empty.stream().anyMatch(n -> n > 100));
}

Output:

true
false

If an empty list should give false, check !list.isEmpty() separately.

Thanks for reading!

Short answer

At least one and none

Stopping at the first answer

Common mistake

Functions used in this recipe

Thanks for reading!