How to resolve the algorithm Function composition step by step in the Java programming language

Published on 12 May 2024 09:40 PM
#Java

How to resolve the algorithm Function composition step by step in the Java programming language

Table of Contents

Problem Statement

Create a function, compose,   whose two arguments   f   and   g,   are both functions with one argument.

The result of compose is to be a function of one argument, (lets call the argument   x),   which works like applying function   f   to the result of applying function   g   to   x.

Reference: Function composition Hint: In some languages, implementing compose correctly requires creating a closure.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Function composition step by step in the Java programming language

The code shows three different implementations of a function composition in Java. Function composition is the process of creating a new function by combining two existing functions. In the first implementation, the compose function takes two functions f and g and returns a new function h that applies g to its argument and then applies f to the result. This is implemented using an anonymous inner class that implements the Fun interface. The second implementation uses the Function interface introduced in Java 8, which provides a more concise syntax for function composition. The third implementation is similar to the second, but it uses a generic type parameter for the type of the input and output of the composed function. All three implementations produce the same result when applied to the sine and arcsine functions: they return the value of the sine of the arcsine of 0.5, which is 0.5.

Source code in the java programming language

public class Compose {

    // Java doesn't have function type so we define an interface
    // of function objects instead
    public interface Fun<A,B> {
        B call(A x);
    }

    public static <A,B,C> Fun<A,C> compose(final Fun<B,C> f, final Fun<A,B> g) {
        return new Fun<A,C>() {
            public C call(A x) {
                return f.call(g.call(x));
            }
        };
    }

    public static void main(String[] args) {
        Fun<Double,Double> sin = new Fun<Double,Double>() {
            public Double call(Double x) {
                return Math.sin(x);
            }
        };
        Fun<Double,Double> asin = new Fun<Double,Double>() {
            public Double call(Double x) {
                return Math.asin(x);
            }
        };

        Fun<Double,Double> sin_asin = compose(sin, asin);

        System.out.println(sin_asin.call(0.5)); // prints "0.5"
    }
}


import java.util.function.Function;

public class Compose {
    public static void main(String[] args) {
        Function<Double,Double> sin_asin = ((Function<Double,Double>)Math::sin).compose(Math::asin);

        System.out.println(sin_asin.apply(0.5)); // prints "0.5"
    }
}


import java.util.function.Function;

public class Compose {
    public static <A,B,C> Function<A,C> compose(Function<B,C> f, Function<A,B> g) {
        return x -> f.apply(g.apply(x));
    }

    public static void main(String[] args) {
        Function<Double,Double> sin_asin = compose(Math::sin, Math::asin);

        System.out.println(sin_asin.apply(0.5)); // prints "0.5"
    }
}

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