How to sort a two dimensional array using `Comparator` interface?

Question

I need to sort the following array:

String [][] myArray = {{"John", "3", "10"}, {"Paul", "16","2"}, 
                       {"Mike","8","20"},    {"Peter","5","0"}};

into the following array:

String [][] myArray = {{"John", "3", "10"}, {"Mike","8","20"}, 
                       {"Paul", "16","2"}, {"Peter","5","0"}};

I have two classes. The first one contains the array, the other one implements Comparator interface. This is the MyArray class:

public class MyArray {
public static void main(String[] args) {
String [][] myArray = {{"John", "3", "10"}, {"Paul", "16","2"}, 
                       {"Mike","8","20"},{"Peter","5","0"}};
ByName byName = new ByName();
Arrays.sort(myArray,byName);
}
}

This is the ByName class:

  import java.util.Comparator;
    public class ByName implements Comparator {
         public int compare(Object o1, Object o2) {
            String name1 = (String)((MyArray) o1)[0]);
            String name2 = (String)((MyArray) o2)[0]);
    return (name1>name2) ? 1 : -1;
// Here I am confused, how can I compare it, how can I sort my array 
// alphabetically by the first element of each element, i.e. by the names. 
            }
    }

This would be more straightforward if you had a 1d array of an object with name, num1, num2 fields, then the object could implement comparable. — Thomas
– Thomas, Commented Apr 21, 2013 at 4:11

Sergey Kalinichenko · Accepted Answer · 2013-04-21 04:18:39Z

5

You almost got it: instead of < in

return (name1>name2) ? 1 : -1;

use compareTo():

String name1 = ((String[])o1)[0];
String name2 = ((String[])o2)[0];
return name1.compareTo(name2);

edited Apr 21, 2013 at 4:18

answered Apr 21, 2013 at 4:09

Sergey Kalinichenko

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4 Comments

Buras Over a year ago

Thank You, but I still got problems in this line: String name1 = (String)((MyArray) o1)[0]); it does not compile

Thomas Over a year ago

As written, you're not actually comparing MyArray, you're passing in the String[][] itself(first argument to Arrays.sort).

shiladitya Over a year ago

the objects being compared are not of type MyArray. They are String[] each. So just remove that cast as correctly shown in the above answer

Sergey Kalinichenko Over a year ago

@Thomas Yes, that's what OP's doing in his main. I guess there's a confusion between MyArray class and myArray local.

user2334113 · Accepted Answer · 2013-04-30 00:38:47Z

3

You can also use an object of a class instead of the two dimensional arrays:

import java.util.Comparator;
    public class ByName implements Comparator {
         public int compare(Object o1, Object o2) {
            String name1 = (String)(( o1));
            String name2 = (String)((o2));
    return (name1>name2) ? 1 : -1;

answered Apr 30, 2013 at 0:38

user2334113

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