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??7, 6, 5, ...
Comparator<Integer> comparator = new Comparator<Integer>() {
@Override
public int compare(Integer o1, Integer o2) {
return o2 - o1;
}
};

??8
Comparator<Integer> comparator = (o1, o2) -> o2 - o1;

???(lambda expression)
●? ??? ????, ??????? ??? ?? ??
? ? ?? ?? ?? ??
o? ?? ?? ???? ??: Ruby, C#, Python,
o? ???? ??? ??? ?? ?
§?? scala: someList.filter(x => x > 0)
●? ???(Functional) ???? ??? 1?(first-
level class)?
o? ??? ??? ??, ????? ???? ? ??
●? ??? ??? ???...?

??8? ???
●? ???(Functional) ?????? ?? ??? ?
???? ??
o? ??? ?????: ?? ???? 1?? ?????
public interface Comparator<T> {
int compare(T o1, T o2);
}
Comparator<Long> comp = (Long o1, Long o2) -> o2 - o1 < 0 ? -1 : 1

???? ??
(Long val1, String val2) -> val1 + val2.length()
???? ?? ?

? ?? ??? ?
public interface Operator<T> {
public T operate(T op1, T op2);
}
public interface Callable<V> {
V call() throws Exception;
}
public interface Runnable {
public void run();
}
public interface Predicate<T> {
boolean test(T t);
}
// ???? ?? ??
Comparator<Long> longComparator =
(Long first, Long second) -> Long.compare(first, second);
// ???? ?? ???? ??, ???? ??
Comparator<Long> longComparator =
(first, second) -> Long.compare(first, second);
// ????? ? ?? ??, ???? ??? ?? ??
Predicate<String> predicate = t -> t.length() > 10;
// ????? ?? ??
Callable<String> callable = () -> "noparam";
// ?? ?? ?? ??
Runnable runnable = () -> System.out.println("no return");
// ?? ??? ??? ??, return? ???? ?? ?? ??
Operator<Integer> plusSquareOp = (op1, op2) -> {
int result = op1 + op2;
return result * result;
};

???? ?? ??
int multiple = 10;
Operator<Integer> operator = (x) -> x * multiple;
int result = operation( operator );
?? ??(free variable):
???? ????? ? ???? ???? ?? ??
●? ??? ????? ???? ????? ?? ??? ? ??
●? ?? ??? ?? ?? ??? ??? final? ???? ???, ????
?? ?? ??? ?? ??? ??? ????? ??? ???? ??

? ?? ?? ??? ??? ?????
java.util.function ???? ??? ??
? ??? ? ?? ??? ????? ?
??
public interface Function<T, R> {
R apply(T t);
}
public interface Predicate<T> {
boolean test(T t);
}
public interface BiFunction<T, U, R> {
R apply(T t, U u);
}
public interface Supplier<T> {
T get();
}
public interface Consumer<T> {
void accept(T t);
}

??? ????? ??
●? @FuntionalInterface ??
o? @FuntionalInterface? ?? ?????? ?? ????
? ? ?? ??? ??? ?? ??!
@FunctionalInterface
public interface Operator<T> {
public T operate(T op1, T op2);
}

??? ????
?? ??
public class SomeView
implements OnClickListener {
private void init() {
myBtn.setOnClickListener(this);
youBtn.setOnClickListener(this);
}
@Override
public void onClick(ClickEvent e) {
…
if (e.getSource() == myBtn) {
...
}
}
}
??? ???? ??
public class SomeView {
private void init() {
myBtn.setOnClickListener(this::onMyBtnClick);
youBtn.setOnClickListener(this::onYouBtnClick);
}
private void onMyBtnClick(ClickEvent e) {
...
}
private void onYouBtnClick(ClickEvent e) {
...
}
}

??? ???? ??
●? ???::?????
o? someOperation( Op::square );
§?? someOperation( (x, y) -> Op.square(x, y) );
●? ??::???????
o? someOperation( obj::square );
§?? someOperation( (x, y) -> obj.square(x, y) );
o? someOperation( this::square );
o? someOperation( super::square );
●? ???::???????
o? someOperation( XClass::double )
§?? someOperation( (x, y) -> x.double(y) )

?????? ??
●? ??? ???(default method)
o? ????? ???? ??? ?? ? ??
●? ?? ???
o? ?????? ?? ???? ?? ? ??

??? ???
public interface Collection<E> extends Iterable<E> {
Iterator<E> iterator();
default boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
boolean removed = false;
final Iterator<E> each = iterator();
while (each.hasNext()) {
if (filter.test(each.next())) {
each.remove();
removed = true;
}
}
return removed;
}
LinkedList<Long> list = ….;
list.removeIf((e) -> e > 10L);

??? ???? ?? ??
class Team {
public int version() {
return 0;
}
}
interface Verion {
default int version() {
return -1;
}
}
interface Lockable {
default int version() {
return 1;
}
}
class ExtTeam
extends Team
implements Version {
}
?? ???? ???? ??
- ExtTeam ??? getVersion()?
Team ???? getVersion() ??
class Job implements
Version, Lockable {
@Override
public int version() {
return Version.super.getName()
}
}
???? ??????? ?? ????
? ?? ??? ? ? ??? ??? ??
?? ???,
?? ???? ???? ??? ?

Optional? ???? ??
●? java.util.Optional???
o? ?? ??? ?? ?? ??? ???? ?? ???
o? ??? ?
§?? Optional<Long> value = someMethod();
if (value.isPresent()) {
Long val = value.get();
}
o? map, filter ?? ???(higher order) ??? ??
§?? public Optional map(Function<? super T, ? extends U> mapper)
§?? public Optional<T> filter(Predicate<? super T> predicate)
§?? public Optional flatMap(Function<? super T, Optional> mapper)

Optional? ???? ??
●? Optional? ??? ??? ??
Optional<Member> mem = findMemberById(1L);
Coord result = mem.map(Member::getAddress)
.map(address -> address.getZipCode())
.map(zipCode -> findCoord(zipCode))
.orElse(null);
Member mem = findMemberById(1L);
Coord result = null;
if (mem != null) {
if (mem.getAddress() != null) {
String zipCode = mem.getAddress().getZipCode();
if (zipCode != null) result = findCoord(zipCode);
}
}

??
●? ??8 ???API: ??? ????? ??
o? filter(Predicate)
o? map(Function)
o? sorted(Comparator)
o? forEach(Consumer)
o? reduce(identity, BinaryOperator)
o? …

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