如何在 Java 中用比较器实现选择排序

Question

I am developing a program to perform selection sort on a list of strings. The input for the program is 6 strings. The output for the program should be the list of strings sorted by their last character.

Here is what I have tried

import java.util.Arrays;
import java.util.Scanner;
import java.util.List;
import java.util.Comparator;

public class Exercise_20_21 {
    public static void main(String args[]) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter 6 strings: ");
        // Step 1: proccess strings from input
        String data = input.next();
        String[] list = data.split(" ");
        for(int i=0; i < list.length; i++){
            System.out.print(list[i]+" ");
        }
        selectionSort(list, new Comparator<String>(){
            @Override
            public int compare(String w1, String w2){
                if(w1.charAt(0) > w2.charAt(0)){
                    return -1;
                }
                else if( w1.charAt(0) < w2.charAt(0)){
                    return 1;
                }
                else {
                    return 0;
                }
            }
        });
        for(int i=0; i < list.length; i++){
            System.out.print(list[i]+" ");
        }
    }

    

    public static <E> void selectionSort(E[] list, Comparator<? super E> comparator) {
        Arrays.sort(list,comparator);
    }
}

Expected:

Enter 5 strings: red blue green yellow orange pink
red blue orange pink green yellow

Actual:

Enter 6 strings: red blue green yellow orange pink
red red

How can I start on debugging this code?

Answer 1

The problem with your code is not with the comparator itself. You would want to use input.nextLine() for being able to read an entire line. Using next will read only until the next delimiter (which is space in your case).

For the comparator part, Java already provides a comparator for comparing strings and other objects. This is Comparator.naturalOrder() and can be used as such:

public static void main(String args[]) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter 6 strings: ");
    // Step 1: proccess strings from input
    String data = input.nextLine();
    String[] list = data.split(" ");

    System.out.println(Arrays.toString(list));

    selectionSort(list, Comparator.naturalOrder());

    for (String s : list) {
        System.out.print(s + " ");
    }
}


public static <E> void selectionSort(E[] list, Comparator<? super E> comparator) {
    Arrays.sort(list, comparator);
}