the vault | Functional Interface

Interface with only one abstract method.

A interface that transforms something into something can be made into a functional interface:

@FunctionalInterface
interface Transformer <T, R> {
	R transform(T t);
}

We can then create an implementation of this interface by initialising it to a lambda expression.

Given we want to implement a transformer that takes a person and retrieves their name:

Transformer<Person, String> getName = x -> x.getName();

Similarly, we can use a lambda as closure:

Capturing a distanceTo function from the Point class:

Point origin = new Point(0, 0);
Transformer<Point, Double> dist = origin::distanceTo;

The lambda also stores the data from the environment it is defined in, and thus the lambda is considered a closure.

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