The document discusses Java 8 lambda expressions and how they can be used to filter, map, and reduce collections. It provides examples of filtering a list of employees to only those over age 60, mapping a list of employees to a list of their full names, and reducing a list of employees to calculate their total salary. It notes how lambda expressions allow bulk data operations on collections in a similar manner to SQL queries.

1. λ

3. functions as values
var square = function(x) { return x * x };
var apply = function(data, func) {
return func(data);
}
console.log(apply(10, square));

4. Ang Java ay parang
kami ng ex ko...
..wala paring closure.
- anon

5. Anonymous Inner Classes
Collections.sort(personList, new Comparator<Person>(){
public int compare(Person p1, Person p2){
return p1.firstName.compareTo(p2.firstName);
}
});

6. Anonymous Inner Classes
Collections.sort(personList, new Comparator<Person>(){
public int compare(Person p1, Person p2){
return p1.firstName.compareTo(p2.firstName);
}
});
Lambda Expressions
Collections.sort(personList, (Person p1, Person p2) ->
p1.firstName.compareTo(p2.firstName));

7. Lambda Expressions
Collections.sort(personList, (Person p1, Person p2) ->
p1.firstName.compareTo(p2.firstName));
Lambda Exp. (shorter)
Collections.sort(personList,
(p1, p2) -> p1.firstName.compareTo(p2.firstName));

8. JEP 107
Bulk Data Operations
for Collections
(e.g filter/map/reduce)

9. filter
List<Employee> old = new ArrayList<Employee>();
for (Employee e : employeeList) {
if (e.age() > 60) {
old.add(e);
}
}

10. filter
List<Employee> old = new ArrayList<Employee>();
for (Employee e : employeeList) {
if (e.age() > 60) {
old.add(e);
}
}
List<Employee> old = employeeList.stream()
.filter(e -> e.age() > 60)
.collect(
Collectors.toCollection(
() -> new ArrayList<>()
)
);

11. filter
List<Employee> old = new ArrayList<Employee>();
for (Employee e : employeeList) {
if (e.age() > 60) {
old.add(e);
}
}
List<Employee> old = employeeList.stream()
.filter(e -> e.age() > 60)
.collect(Collectors.toCollection(
() -> new ArrayList<>()));

12. filter
List<Employee> old = new ArrayList<Employee>();
for (Employee e : employeeList) {
if (e.age() > 60) {
old.add(e);
}
}
List<Employee> old = employeeList.stream()
.filter(e -> e.age() > 60)
.collect(
Collectors.toCollection(
ArrayList::new
)
);

13. filter
List<Employee> old = new ArrayList<Employee>();
for (Employee e : employeeList) {
if (e.age() > 60) {
old.add(e);
}
}
List<Employee> old = employeeList.stream()
.filter(e -> e.age() > 60)
.collect(Collectors.toCollection(ArrayList::new));

14. filter
List<Employee> old = new ArrayList<Employee>();
for (Employee e : employeeList) {
if (e.age() > 60) {
old.add(e);
}
}
List<Employee> old = employeeList.stream()
.filter(e -> e.age() > 60)
.collect(Collectors.toList());

15. map
List<String> names = new ArrayList<String>();
for (Employee e : employeeList) {
names.add(e.firstName() + " " + e.lastName());
}

16. map
List<String> names = new ArrayList<String>();
for (Employee e : employeeList) {
names.add(e.firstName() + " " + e.lastName());
}
List<String> names = employeeList.stream()
.map(e -> e.firstName() + " " + e.lastName())
.collect(Collectors.toList());

17. reduce
BigDecimal totalSalary = BigDecimal.ZERO;
for (Employee e : employeeList) {
totalTax = totalTax.add(e.salary());
}

18. reduce
BigDecimal totalSalary = BigDecimal.ZERO;
for (Employee e : employeeList) {
totalTax = totalTax.add(e.salary());
}
BigDecimal totalSalary = employeeList.stream()
.reduce(BigDecimal.ZERO,
(sum, e) -> sum.add(e.salary()),
(bd1, bd2) -> bd1.add(bd2));

19. reduce
BigDecimal totalSalary = BigDecimal.ZERO;
for (Employee e : employeeList) {
totalTax = totalTax.add(e.salary());
}
BigDecimal totalSalary = employeeList.stream()
.reduce(BigDecimal.ZERO,
(sum, e) -> sum.add(e.salary()),
BigDecimal::add);

20. chaining
BigDecimal totalOldTax = employeeList.stream()
.filter(e -> e.age() > 60)
.map(e -> e.salary().multiply(e.taxRate()))
.reduce(BigDecimal.ZERO,
(sum, tax) -> sum.add(tax);

21. just like SQL
BigDecimal totalOldTax = employeeList.stream()
.filter(e -> e.age() > 60)
.map(e -> e.salary().multiply(e.taxRate()))
.reduce(BigDecimal.ZERO,
(sum, tax) -> sum.add(tax);
SELECT SUM(salary * tax_rate)
FROM employees
WHERE age > 60;

22. just like SQL
filter() => WHERE, GROUP BY
map()
=> SELECT, inline query
reduce() => aggregate functions
sort()
=> ORDER BY

23. λ
Java 8

24. Where to get Lambda
Project Page
http://openjdk.java.net/projects/lambda/
JDK8
http://jdk8.java.net/download.html
JDK8 w/ Lambda
http://jdk8.java.net/lambda/
NetBeans Nightly
http://bertram2.netbeans.org:8080/job/jdk8lambda/lastSuccessfulBuild/artifact/nbbuild/

25. Thank you for listening!
bryanbibat.net | @bry_bibat
speakerdeck.com/bryanbibat