Nested use of Java function generics

Nested generics allow the use of other generic types within generic methods, creating highly reusable code. In practice, nested generics can be used to find two peak elements in an array. The sample code uses the generic Pair to store the results and finds the peak value by iteratively checking the elements and comparing them with adjacent elements.

Nested use of Java function generics

Generics are a powerful Java language feature that allows us to create Reusable code that can operate on a variety of data types. Function generics allow us to use generics within functions, thus increasing flexibility.

Nested generics

Nested generics refer to using other generic types inside generic methods. This allows us to create highly reusable code, especially when dealing with complex data structures.

The following is an example of a nested generic:

public class Pair<T, U> {
    private T first;
    private U second;

    public Pair(T first, U second) {
        this.first = first;
        this.second = second;
    }

    public T getFirst() {
        return first;
    }

    public U getSecond() {
        return second;
    }
}

The Pair class is a nested generic that stores two elements of different types.

Practical case

Let us consider a scenario where we need to return an array nums of two peak elements. A peak element is an element that is larger than its neighboring elements.

The following is a Java code using nested generics:

public class FindPeakElements {

    public static <T extends Comparable<T>> Pair<T, T> findPeakElements(T[] nums) {
        if (nums == null || nums.length < 3) {
            throw new IllegalArgumentException("Invalid array size");
        }

        T firstPeak = nums[0];
        T secondPeak = nums[nums.length - 1];

        for (int i = 1; i < nums.length - 1; i++) {
            T current = nums[i];
            T prev = nums[i - 1];
            T next = nums[i + 1];

            if (current > prev && current > next) {
                if (current > firstPeak) {
                    secondPeak = firstPeak;
                    firstPeak = current;
                } else if (current > secondPeak) {
                    secondPeak = current;
                }
            }
        }

        return new Pair<>(firstPeak, secondPeak);
    }

    public static void main(String[] args) {
        Integer[] nums = {1, 2, 3, 4, 5, 6, 7, 6, 5, 4, 3, 2, 1};
        Pair<Integer, Integer> peaks = findPeakElements(nums);
        System.out.println("First peak: " + peaks.getFirst());
        System.out.println("Second peak: " + peaks.getSecond());
    }
}

This code uses nested generics Pair to store two peak elements. It finds the peak element by iterating through the array and checking if the element is larger than its neighbors.

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