Step by Step solution about How to resolve the algorithm Apply a callback to an array step by step in the Java programming language

First example

In this example, we define two functional interfaces, IntConsumer and IntToInt, which represent functions that consume an integer and produce nothing and a function that consumes an integer and produces an integer, respectively.

Then, we define two methods, forEach and update, which take an array of integers and a function as arguments.

• The forEach method iterates over the array and calls the function for each element in the array.
• The update method iterates over the array and updates each element in the array by calling the function with the current element as an argument.

In the main method, we create an array of integers and pass it to the forEach method along with an anonymous inner class that implements the IntConsumer interface.

• The run method of this class simply prints the value of the integer passed to it.

Next, we pass the same array to the update method along with an anonymous inner class that implements the IntToInt interface.

• The run method of this class squares the value of the integer passed to it.

Finally, we again pass the array to the forEach method along with another anonymous inner class that implements the IntConsumer interface.

• The run method of this class prints the value of the integer passed to it. The output of this program is:

1
2
3
4
5
6
7
8
9
10
1
4
9
16
25
36
49
64
81
100

Second example

In this example, we use the Java 8 Streams API to perform the same operations on the array of integers.

• The map method takes a function that consumes an integer and produces an integer as an argument and applies it to each element in the stream.
• The reduce method takes a function that consumes two integers and produces an integer as an argument and applies it to the elements in the stream to produce a single result.

In this case, we use the map method to cube each element in the stream and the reduce method to sum the cubes of the elements in the stream. The output of this program is:

27
512
1024
2048
35937
3025
4913
8192
13824
21952
sum: 86621

public class ArrayCallback7 {

    interface IntConsumer {
        void run(int x);
    }

    interface IntToInt {
        int run(int x);
    }

    static void forEach(int[] arr, IntConsumer consumer) {
        for (int i : arr) {
            consumer.run(i);
        }
    }

    static void update(int[] arr, IntToInt mapper) {
        for (int i = 0; i < arr.length; i++) {
            arr[i] = mapper.run(arr[i]);
        }
    }

    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

        forEach(numbers, new IntConsumer() {
            public void run(int x) {
                System.out.println(x);
            }
        });

        update(numbers, new IntToInt() {
            @Override
            public int run(int x) {
                return x * x;
            }
        });

        forEach(numbers, new IntConsumer() {
            public void run(int x) {
                System.out.println(x);
            }
        });
    }
}


import java.util.Arrays;

public class ArrayCallback {

    public static void main(String[] args) {
        int[] myIntArray = {1, 2, 3, 4, 5};

        int sum = Arrays.stream(myIntArray)
                .map(x -> {
                    int cube = x * x * x;
                    System.out.println(cube);
                    return cube;
                })
                .reduce(0, (left, right) -> left + right); // <-- could substitute .sum() for .reduce(...) here.
        System.out.println("sum: " + sum);
    }
}