供給型介面

Supplier<T>     返回T型別物件
    T get();

Supplier<Apple> supplier = () -> new Apple();
// Supplier<Apple> supplier = Apple::new;
supplier.get();

消費型介面

Consumer<T>     接收一個 T 型別
    void accept(T t);

List<String> languages = Arrays.asList("java","scala","python");
Consumer<String> consumer = System.out::println;
languages.stream().forEach(consumer);
 

函式型介面

Function<T, R>  由T型別物件轉成R型別物件
    R apply(T t);

List<String> languages = Arrays.asList("java","scala","python");
Function<String, Integer> ti = String::length;
languages.stream()
    .map(ti)
    .forEach(System.out::println);

斷言型介面

Predicate<T>    條件判斷
    boolean test(T t);
 

List<String> languages = Arrays.asList("java","scala","python");
Predicate<String> p = (str) -> str.length() > 4;
languages.stream()
    .filter(p)
    .forEach(System.out::println);

一個簡單的使用多個函式式介面的例子：

List<String> languages = Arrays.asList("java","scala","python");
Function<String, Integer> ti = String::length;
BiConsumer<Integer, String> bi = (a, b) -> System.out.println(b + a);
IntPredicate ip = x -> x > 4;
IntPredicate ip1 = x -> x < 100;
IntUnaryOperator io = x -> x * x;
languages.stream()
    .map(ti)
    .map(io::applyAsInt)
    .filter(x->ip.and(ip1).test(x))
    .forEach(x -> bi.accept(x, "prefix_"));
 

部分函式式介面中有 default 方法， 可以進行組合使用！