Этот тест показывает, что ваш второй вариант может работать значительно лучше. Сначала выведите код:
one filter with predicate of form u -> exp1 && exp2, list size 10000000, averaged over 100 runs: LongSummaryStatistics{count=100, sum=4142, min=29, average=41.420000, max=82}
two filters with predicates of form u -> exp1, list size 10000000, averaged over 100 runs: LongSummaryStatistics{count=100, sum=13315, min=117, average=133.150000, max=153}
one filter with predicate of form predOne.and(pred2), list size 10000000, averaged over 100 runs: LongSummaryStatistics{count=100, sum=10320, min=82, average=103.200000, max=127}
теперь код:
enum Gender {
FEMALE,
MALE
}
static class User {
Gender gender;
int age;
public User(Gender gender, int age){
this.gender = gender;
this.age = age;
}
public Gender getGender() {
return gender;
}
public void setGender(Gender gender) {
this.gender = gender;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
static long test1(List<User> users){
long time1 = System.currentTimeMillis();
users.stream()
.filter((u) -> u.getGender() == Gender.FEMALE && u.getAge() % 2 == 0)
.allMatch(u -> true); // least overhead terminal function I can think of
long time2 = System.currentTimeMillis();
return time2 - time1;
}
static long test2(List<User> users){
long time1 = System.currentTimeMillis();
users.stream()
.filter(u -> u.getGender() == Gender.FEMALE)
.filter(u -> u.getAge() % 2 == 0)
.allMatch(u -> true); // least overhead terminal function I can think of
long time2 = System.currentTimeMillis();
return time2 - time1;
}
static long test3(List<User> users){
long time1 = System.currentTimeMillis();
users.stream()
.filter(((Predicate<User>) u -> u.getGender() == Gender.FEMALE).and(u -> u.getAge() % 2 == 0))
.allMatch(u -> true); // least overhead terminal function I can think of
long time2 = System.currentTimeMillis();
return time2 - time1;
}
public static void main(String... args) {
int size = 10000000;
List<User> users =
IntStream.range(0,size)
.mapToObj(i -> i % 2 == 0 ? new User(Gender.MALE, i % 100) : new User(Gender.FEMALE, i % 100))
.collect(Collectors.toCollection(()->new ArrayList<>(size)));
repeat("one filter with predicate of form u -> exp1 && exp2", users, Temp::test1, 100);
repeat("two filters with predicates of form u -> exp1", users, Temp::test2, 100);
repeat("one filter with predicate of form predOne.and(pred2)", users, Temp::test3, 100);
}
private static void repeat(String name, List<User> users, ToLongFunction<List<User>> test, int iterations) {
System.out.println(name + ", list size " + users.size() + ", averaged over " + iterations + " runs: " + IntStream.range(0, iterations)
.mapToLong(i -> test.applyAsLong(users))
.summaryStatistics());
}