Given the List<String> need to sort it in given alphabetical order using stream and comparator

Question

given list and set of letters to sort the list using java stream

List<String> names= Arrays.asList("Robin","Zax","John");
String order = "ZALBKNDWMTFCGOIUHEPQXSYVRJ";

EXAMPLE: Input: List names= Arrays.asList("Robin","Zax","John"); String order = "ZJR"

Output: ["Zax","John","Robin"]

Input 2: List<String> names= Arrays.asList("Robin","Zax","John","Rohan"); String order = "OZJRHBAS";

OUTPUT: ["Zax","John","Rohan","Robin"]

 names.stream().sorted(new MyComparator(order)).collect(Collectors.toList()).forEach(System.out::println);

I just want the implementation of compare method below is what i have tried but its sorting on the basis of only first letter. Is there any way it can be done in such a way the all the letters of string are taken care for sorting.

class MyComparator implements Comparator<String> {
    private String order;

    MyComparator(String order) {
        this.order = order;
    }

    @Override
    public int compare(String s1, String s2) {
        char[] charsOfS1 = s1.toCharArray();
        char[] charsOfS2 = s2.toCharArray();
        int proximity = 0;
        for(int i=0; i<Math.min(charsOfS1.length,charsOfS2.length);i++){
            int check = order.indexOf(s1.charAt(i)) - order.indexOf((s2.charAt(i)));
            if(check<0)
                proximity--;
            else if(check>0)
                proximity++;
        }
        return proximity;
    }
}

"I just want the implementation of compare method" - okay, so what are the actual requirements? How far have you got in implementing them? We really don't have nearly enough information to help you at the moment. — Jon Skeet
– Jon Skeet, Commented Nov 14, 2022 at 8:47
given alphabetical order using stream and comparator -> "Zax","John","Robin" or "Zax","Robin","John" !! for a solution maybe -> return o2.compareTo(o1); — Youcef LAIDANI
– Youcef LAIDANI, Commented Nov 14, 2022 at 8:57
just take the 1st char of each name, get their positions in the order string, and compare the 2 positions themselves — BigMike
– BigMike, Commented Nov 14, 2022 at 9:01
@JonSkeet I just want to make use of order given for sorting the string names in compare method, If i do return o2.compareTo(o1); it will not sort it in given order it will sort it in default alphabetical order. — ITGeek
– ITGeek, Commented Nov 14, 2022 at 9:07

Arvind Kumar Avinash · Accepted Answer · 2022-11-14 09:08:59Z

1

You can simply compare the index position of the first character of strings:

public int compare(String s1, String s2) {
    return order.indexOf(s1.charAt(0)) - order.indexOf((s2.charAt(0)));
}

Full Demo:

import java.util.Comparator;
import java.util.List;
import java.util.Arrays;
import java.util.stream.Collectors;

class MyComparator implements Comparator<String> {
    private String order;

    MyComparator(String order) {
        this.order = order;
    }

    @Override
    public int compare(String s1, String s2) {
        return order.indexOf(s1.charAt(0)) - order.indexOf((s2.charAt(0)));
    }
}

public class Main {
    public static void main(String[] args) {
        // Test
        List<String> names = Arrays.asList("Robin", "Zax", "John");
        String order = "ZJR";
        System.out.println(names.stream().sorted(new MyComparator(order)).toList());
    }
}

Output:

[Zax, John, Robin]

answered Nov 14, 2022 at 9:08

Arvind Kumar Avinash

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2 Comments

ITGeek Over a year ago

But if you compare only charAt(0) it will sort it on the basis of first letter for example: ` List<String> names= Arrays.asList("Robin","Zax","John","Rohan"); String order = "OZJRHBAS"; ` the OUTPUT will be Zax John Robin Rohan but here Rohan should come before Robin.

Jon Skeet Over a year ago

@vishal: It's almost as if you haven't provided complete requirements...

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