Functional Interfaces

Interfaces with single abstract method

5 min read

Functional Interfaces

Functional interfaces have exactly one abstract method and support lambda expressions.

Code Examples

Lambda with functional interface

java
1
2@FunctionalInterface
3interface Calculator {
4    int add(int a, int b);
5}
6
7Calculator c = (a, b) -> a + b;
8System.out.println(c.add(2, 3));
9

Use Cases

  • Lambda expressions
  • Streams API
  • Callbacks

Common Mistakes to Avoid

  • Adding more than one abstract method