Sort a string array with Collections based on the content of the split string-CodePudding

I have a String array where there is a white space in the middle. I want to sort the contents based on the first substring before the white space, and then the substring after the white space.

For example, if my array looks like this: {"Henry 123", "Henry 234", "David 123", "David 234"}, in the end I want {"David 123", "David 234", "Henry 123", "Henry 234"}.

I tried implement a new comparator below:

import java.util.*;

public class MyClass {
    public static void main(String args[]) {
        String[] str_arr = {"Henry 123", "Henry 234", "David 123", "David 234"};

        Collections.sort(str_arr, new Comparator<String>(){
            
            public int compare(String s1, String s2) {
                String[] str1 = s1.split(" ");
                String[] str2 = s2.split(" ");
                if(str1[0].compareTo(str2[0]) != 0) {
                    return str1[0].compareTo(str2[0]);
                }
                return str1[1].compareTo(str2[1]); 
            }            
        });
        
        for (int i = 0; i < str_arr.length; i  ) {
            System.out.printf("%s, ", str_arr[i]);
        }
    }
}

But I am getting this error:

MyClass.java:7: error: no suitable method found for sort(String[],<anonymous Comparator>) Collections.sort(str_arr, new Comparator(){ ^ method Collections.<T#1>sort(List<T#1>) is not applicable (cannot infer type-variable(s) T#1 (actual and formal argument lists differ in length)) method Collections.<T#2>sort(List<T#2>,Comparator<? super T#2>) is not applicable (cannot infer type-variable(s) T#2 (argument mismatch; String[] cannot be converted to List<T#2>)) where T#1,T#2 are type-variables: T#1 extends Comparable<? super T#1> declared in method <T#1>sort(List<T#1>) T#2 extends Object declared in method <T#2>sort(List<T#2>,Comparator<? super T#2>) 1 error

This error sounds like Collections framework does not support sorting strings, which does not make much sense.

CodePudding user response：

Here is one way.

String[] arr = { "Henry 123", "Henry 234", "David 123",
        "David 234" };

Comparator<String> comp =
        Comparator.comparing((String a) -> a.split("\\s ")[0])
                .thenComparing(a -> a.split("\\s ")[1]);

Arrays.sort(arr,comp);
System.out.println(Arrays.toString(arr))

prints

[David 123, David 234, Henry 123, Henry 234]

If you want to compare the second value as an int then change to.

...thenComparingInt(a -> Integer.parseInt(a.split("\\s ")[1]));

Remember that comparing numbers as strings is lexical not numerical so the results can vary. For example, comparing [55, 123] as strings would result in [123, 55] since 55 is lexically greater than 123. And the reason your solution didn't work is that arrays are not collections which is what Collections.sort() expects.

CodePudding user response：

You have a String array, which the Collection.sort method indeed does not support sorting. Collections.sort is for sorting Lists.

You should use Arrays.sort instead:

Arrays.sort(str_arr, (s1, s2) -> {
    String[] str1 = s1.split(" ");
    String[] str2 = s2.split(" ");
    int firstPartcomparison = str1[0].compareTo(str2[0]);
    if(firstPartcomparison != 0) {
        return firstPartcomparison;
    }
    return str1[1].compareTo(str2[1]);
});