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What is a functional interface?
- An Interface that contains exactly one abstract method is known as a functional interface.
- A functional interface can have any number of default, static methods but can contain only one abstract method. It can also declare methods of the object class.
- Functional Interface is also known as Single Abstract Method Interfaces or SAM Interfaces. It is a new feature in Java 8, which helps to achieve a functional programming approach.
- A functional interface can extend another interface only when it does not have any abstract method.
Java @FunctionalInterface Annotation
- The type is an interface type and not an annotation type, enum, or class.
- The annotated type satisfies the requirements of a functional interface.
Java @FunctionalInterface Annotation Example
@FunctionalInterface
interface Sayable{
void say(String msg); // abstract method
}
public class FunctionalInterfacesExample {
public static void main(String[] args) {
Sayable sayable = (msg) - > {
System.out.println(msg);
};
sayable.say("Say something ..");
}
}
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