Chapter 06 Lambdas

• Alles tussen curly braces...
• work with interface with only one abstract method. (functional interface)
• SAM Single Abstract Method (SAM rule)

a -> a.canHop()
// zelfde als:
(Animal a) -> {return a.canHop();}

• single param
• arrow operator to seperate param and body
• one or more lines of code, incl semicolo and return statment.

Geen {} betekent dat ie returned. Gaat niet met 2 of meer return statements.

wel valide....

s->{}
()-> true
a-> a.startsWith("test")
(a,b)-> a.startsWith("test")
(String a, String b) ->a.startsWith("test")

NIET valide

a,b -> a.startsWith("test") // missende boogjes
a -> {a.startsWith("test");} // missende return...
a -> {return a.startsWith("test")} // missende semicolon ;

Functional Interfaces

• Predicate
• Consumer
• Supplier
• Comparator

Predicate

public interface Predicate<T> {
    boolean test(T t);
}

Consumer

void accept(T t)

Supplier

T get()
//
Supplier<Integer> number = () -> 42;
Supplier<Integer> random = () -> newRandom().nextInt();

Comparator

int compate(T o1, T o2)
// ascending sort
Comparator<Integer> ints = (i1,i2) -> i1 -i2;
// descending
Comparator<String> strings = (s1,s2) -> s2.compareTo(s1);
Comparator<String> moreStrings = (s1,s2) -> - s1.compareTo(s2);

Variables in Lambas

Predicate<String> p = x -> true;
Predicate<String> p = (var x) -> true;
Predicate<String> p = (Stringx) -> true;

Local variable in Lambda body

(a,b) -> {init c = 0; return 5;} (a,b) -> {init a = 0; return 5;} // DNC

Variable referenced from the labmda body

• can access instance variable, method params, or local variables
• Method params and local variables are allowed if they are effectively final. (no change after set...)

Calling APIs with Lambdas

RemoveIf()

NOT on a Map! Map heeft keys and values...

sort()

begint met twee vars en returns an int!!

Not a sort on a Set of Map

forEach()

Kan wel op Set of Map, maar dan over de Keys of Values ;-)

ocp 05 ocp 07