Functional Interface

Functional Interface

• An interface that contains exactly one abstract method

• @FunctionalInterface

  • Used to mark an interface as a functional interface

• Usage with Lambda Expressions

  • Lambda expressions provide a simple way to implement functional interface
  • Lambda expression syntax
    • (parameters) -> { body }

  public class Main {
      public static void main(String[] args) {
          CheckEven func = (n) -> (n % 2) == 0;
          System.out.println(func.execute(2)); // true
      }
  }
  
  @FunctionalInterface
  interface CheckEven {
      boolean execute(int number);
  }
  

• Common Function Interface

  • Predicate<T>

    • Represents a function that takes one argument and returns a boolean

    Predicate<Integer> func = (n) -> (n % 2) == 0;
    System.out.println(func.test(10)); // true
    

  • Function<T, R>

    • Represents a function that takes one argument and produces a result

    Function<String, Integer> func = (s) -> s.length();
    System.out.println(func.apply("Hello")); // 5
    

  • BiFunction<T, U, R>

    • Represents a function that takes two arguments and produces a result

  • Consumer<T>

    • Represents a function that takes one argument and returns no result

    Consumer<String> func = (s) -> System.out.println(s);
    func.accept("Hello"); // Hello
    

  • Supplier<T>

    • Represents a function that takes no argument and returns a result

    Supplier<String> func = () -> "Hello";
    System.out.println(func.get()); // Hello
    

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