Streams - Beginning Java 8 Language Features - page 630

else {
System.out.println("max is not defined.");
}
max is not defined.
The following snippet of code prints the details of the highest earner in the person's list:
Optional<Person> person = Person.persons()
.stream()
.reduce((p1, p2) -> p1.getIncome() > p2.getIncome()?p1:p2);
if (person.isPresent()) {
System.out.println("Highest earner: " + person.get());
}
else {
System.out.println("Could not get the highest earner.");
}
Highest earner: (3, Donna, FEMALE, 1962-07-29, 8700.00)
To compute the sum, max, min, average, etc. of a numeric stream, you do not need to use the reduce()
method. You can map the non-numeric stream into one of the three numeric stream types ( IntStream , LongStream ,
or DoubleStream ) and use the specialized methods for these purposes. The following snippet of code prints the
sum of the incomes of all people. Note the use of the mapToDouble() method that converts a Stream<Person> to a
DoubleStream . The sum() method is called on the DoubleStream .
double totalIncome = Person.persons()
.stream()
.mapToDouble(Person::getIncome)
.sum();
System.out.println("Total Income: " + totalIncome);
Total Income : 26000.0
To get the minimum and maximum values of a stream, use the min() and max() methods of the specific stream.
These methods in the Stream<T> interface take a Comparator as argument and return an Optional<T> . They do not
take any arguments in IntStream , LongStream , and DoubleStream interfaces and return OptionalInt , OptionalLong ,
and OptionalDouble , respectively. The following snippet of code prints the details of the highest earner in a list of
people:
Optional<Person> person = Person.persons()
.stream()
.max(Comparator.comparingDouble(Person::getIncome));
if (person.isPresent()) {
System.out.println("Highest earner: " + person.get());
}