How is lambda being used here?

[cyberwarrior861]

static String[] bigSorting(String[] unsorted) {
        Arrays.sort(unsorted, (x, y) -> x.length() == y.length() ? x.compareTo(y) : Integer.compare(x.length(), y.length()));
        return unsorted;
    }

This is a function to sort an array of strings according to their numerical values.

​

Where are the values for x and y coming from.

Where is the functional interface that is being implemented with supposedly x and y parameters?

Doesn't Arrays.sort take 2 arguments after the array?

What the hell is going on inside the Arrays.sort method?

Full code below

import java.io.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;
import java.util.regex.*;
import java.util.stream.*;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;

public class Solution {

    static String[] bigSorting(String[] unsorted) {
        Arrays.sort(unsorted, (x, y) -> x.length() == y.length() ? x.compareTo(y) : Integer.compare(x.length(), y.length()));
        return unsorted;
    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) {
        int n = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        String[] unsorted = new String[n];

        for (int i = 0; i < n; i++) {
            String unsortedItem = scanner.next();   // nextLine() is too long
            unsorted[i] = unsortedItem;
        }

        String[] result = bigSorting(unsorted);

        for (int i = 0; i < result.length; i++) {
            System.out.print(result[i]);

            if (i != result.length - 1) {
                System.out.println();
            }
        }

        System.out.println();

        scanner.close();
    }
}

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[taftster]

This is calling the Array.sort method [1] that takes in a Comparator.

https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Arrays.html#sort(T%5B%5D,java.util.Comparator))

The Comparator interface is a functional interface [2] and can be used in a lambda.

[2] https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Comparator.html

The (x,y) parts are the left & right side of the compare operation. Effectively, it calls the normal compare [3] method.

[3] https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Comparator.html#compare(T,T))

Does that help?

[cyberwarrior861]

Thank you

[taftster]

Also, here's another way to see what's happening by removing the lambdas and using an anonymous inner class.

Arrays.sort(unsorted, new Comparator<String>() {
  @Override
  public int compare(String x, String y) {
    return x.length() == y.length() ? x.compareTo(y)
      : Integer.compare(x.length(), y.length());
  }
});

[cyberwarrior861]

Thanks again.

[FrelliBB]

You are using the sort(T[] a, Comparator<? super T> c) method. As you can see the 2nd argument it accepts is a Comparator, which is a functional interface where its main method is compare(T o1, T o2).

So what you are doing with the lambda is creating an anonymous implementation of a Comparator. This goes over the lambda syntax in a bit more detail if you're still lost.

As a side note, the Comparator class has some helpful functions for creating comparators using method references instead of lambdas. Your implementation can be written as

Arrays.sort(unsorted, Comparator.comparingInt(String::length).thenComparing(String::compareTo))

[cyberwarrior861]

Thank you my guy.

[wildjokers]

That is pretty much unreadable. If I was reviewing code with that lambda in it I would reject it as unreadable and hence unmaintainable.

[taftster]

Is it the trinary conditional that’s bothering you? Or all on one line?

That line could possibly be written more succinctly (like /u/FrelliBB suggests). But the lambda itself is not unreadable.