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Partial Application in Java
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| import java.util.function.Function; | |
| import static java.lang.String.format; | |
| class SamplePartialApplication { | |
| public static void main(String[] args) { | |
| Fx2<Integer, Integer, Integer> add = (x, y) -> x + y; | |
| System.out.println(format("Fully applied function of 2 arity result: %s", add.apply(2, 3))); | |
| Function<Integer, Integer> addTwo = PartialApplication.partial(add, 2); | |
| System.out.println(format("Partially applied 2 to function of two arity: %s", addTwo.apply(3))); | |
| Fx3<Integer, Integer, String, String> descriptiveAdd = (x, y, z) -> z + (x + y); | |
| Fx2<Integer, String, String> firstPartialDescribe = PartialApplication.partial(descriptiveAdd, 2); | |
| Function<String, String> describe5 = PartialApplication.partial(firstPartialDescribe, 3);; | |
| System.out.println(describe5.apply("The result is: ")); | |
| Function<String, String> alternativeDescribe5 = PartialApplication.partial(descriptiveAdd, 2, 3); | |
| System.out.println(alternativeDescribe5.apply("Alternative result is: ")); | |
| } | |
| /** | |
| * Function with arity of 2 | |
| * @param <I1> type of first input | |
| * @param <I2> type of second input | |
| * @param <O> type of output | |
| */ | |
| @FunctionalInterface | |
| public interface Fx2<I1, I2, O> { | |
| /** | |
| * Execute this function | |
| * @param inputOne first input | |
| * @param inputTwo second input | |
| * @return output of this function | |
| */ | |
| O apply(I1 inputOne, I2 inputTwo); | |
| } | |
| /** | |
| * Function with arity of 3 | |
| * @param <I1> type of first input | |
| * @param <I2> type of second input | |
| * @param <I3> type of third input | |
| * @param <O> type of output | |
| */ | |
| @FunctionalInterface | |
| public interface Fx3<I1, I2, I3, O> { | |
| /** | |
| * Execute this function | |
| * @param inputOne first input | |
| * @param inputTwo second input | |
| * @param inputThree third input | |
| * @return output of this function | |
| */ | |
| O apply(I1 inputOne, I2 inputTwo, I3 inputThree); | |
| } | |
| public static class PartialApplication { | |
| public static <I1, I2, O> Function<I2, O> partial(Fx2<I1, I2, O> f, I1 inputOne) { | |
| return i2 -> f.apply(inputOne, i2); | |
| } | |
| public static <I1, I2, I3, O> Function<I3, O> partial(Fx3<I1, I2, I3, O> f, I1 inputOne, I2 inputTwo) { | |
| return i3 -> f.apply(inputOne, inputTwo, i3); | |
| } | |
| public static <I1, I2, I3, O> Fx2<I2, I3, O> partial(Fx3<I1, I2, I3, O> f, I1 inputOne) { | |
| return (i2, i3) -> f.apply(inputOne, i2, i3); | |
| } | |
| } | |
| } |
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