Java 函数式接口（Functional Interface）

1. 基本概念

• 函数式接口就是只定义一个抽象方法的接口
• 注：可以有很多默认方法

1.1 @FunctionalInterface

@FunctionalInterface 可检测接口是否符合函数式接口

1.2 函数描述符

函数式接口的抽象方法的签名基本上就是 Lambda 表达式的签名。我们将这种抽象方法叫作函数描述符

2. 常用函数式接口

public interface Predicate<T> {
    boolean test(T t);
}
public interface Consumer<T> {
    void accept(T t);
}
public interface Supplier<T> {
    T get();
}
public interface Function<T, R> {
    R apply(T t);
}

2.1 函数签名

2.2 例程

Predicate<String> predicate = str -> "aaa".equals(str);
BiPredicate<String, String> biPredicate = (o1, o2) -> o1.equals(o2);
boolean flag = predicate.test("aaa");
boolean flag2 = biPredicate.test("aaa", "111");

Consumer<String> consumer = str -> System.out.println(str);
BiConsumer<String, String> biConsumer = (a, b) -> System.out.println(a + "; " + b);

consumer.accept("222");
biConsumer.accept("aaa", "bbb");

Supplier<OrderDTO> supplier = () -> new OrderDTO();
OrderDTO orderDTO = supplier.get();

Function<Long, String> function = (Long l) -> l.toString();
BiFunction<String, Integer, String> biFunction = (str, i) -> str.substring(i);

String apply = function.apply(1000L);
String apply2 = biFunction.apply("abcde", 2);