1. Computer Science 312
Lambdas in Java 1

2. Syntax of Java Lambdas (<parameters>) -> <expression>
(<parameters>) -> {<statements> ;}
(Apple a) -> a.getWeight() > 150
(Apple a1, Apple a2) ->
a1.getWeight().compareTo(a2.getWeight())
(int x) -> x + 1

3. Context of Use Can be bound to a variable:
Can be passed as an argument to a method or returned as a method’s value:
Must conform to a functional interface in either case
Predicate<Apple> isGreen = (Apple a) -> "green".equals(a.getColor());
List<Apple> greenApples =
filter(inventory, (Apple a) -> "green".equals(a.getColor()));

4. Functional Interfaces
A functional interface specifies exactly one method
The signature of the method is similar to the signature of the lambda expression, which omits the name (called a function descriptor)
public interface Predicate<T>{
boolean test(T t); }
Predicate<Apple> isGreen = (Apple a) ->
"green".equals(a.getColor());
List<Apple> greenApples =
filter(inventory, isGreen);

5. Functional Interface for filter
public interface Predicate<T>{
boolean test(T t); }
public static <T> List<T> filter(List<T> list, Predicate<T> p) {
List<T> results = new ArrayList<>();
for(T s: list){
if(p.test(s)){
results.add(s);
return results;
Predicate<String> nonEmptyStringPredicate = (String s) -> !s.isEmpty();
List<String> nonEmpty = filter(listOfStrings,
nonEmptyStringPredicate);

6. Functional Interface for map
public interface Function<T, R>{
R apply(T t); }
public static <T, R> List<R> map(List<T> list,
Function<T, R> f) {
List<R> results = new ArrayList<>();
for(T s: list){
results.add(f.apply(s));
return results;
List<Integer> lyst = map(Arrays.asList("I", "love", "functions!"),
(String s) -> s.length());

7. Functional Interface for forEach
public interface Consumer<T>{
void accept(T t); }
public static <T> void forEach(List<T> list,
Consumer<T> c) {
for(T s: list){
c.accept(s);
return results;
forEach(Arrays.asList(1,2,3,4,5),
(Integer i) -> System.out.println(i));

8. Specializations for Primitive Types
@FunctionalInterface
public interface IntPredicate{
boolean test(int i); }
IntPredicate evenNumbers = (int i) -> i % 2 == 0;
evenNumbers.test(1000); // Returns true

9. Bifunction Interface Where would this interface be used?
@FunctionalInterface
public interface BiFunction<T, U, V>{
V apply(T o1, U o2); }
Where would this interface be used?

10. Introduction to Streams Chapter 4
For next time
Introduction to Streams
Chapter 4