Functional Interfaces In Java

What to do with it?

A functional interface is an interface that contains only one abstract method. They can have only one functionality to exhibit. From Java 8 onwards, lambda expressions can be used to represent the instance of a functional interface. A functional interface can have any number of default methods. Runnable , ActionListener , Comparable are some of the examples of functional interfaces.

Before Java 8, we had to create anonymous inner class objects or implement these interfaces.

Java 8 onwards, we can assign lambda expression to its functional interface object like this:

@FunctionalInterface Annotation

@FunctionalInterface annotation is used to ensure that the functional interface can’t have more than one abstract method. In case more than one abstract methods are present, the compiler flags an ‘Unexpected @FunctionalInterface annotation’ message. However, it is not mandatory to use this annotation.

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@Override

public void run()

{

System.out.println("New thread created");

}

}).start();

}

}