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Thread: How to sort this?

  1. #1
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    Default How to sort this?

    In my program I have put these in a arrayList:

    String string1 = start + "-" + end;

    So arrayList is full of these string1 things.
    Now start and end are both number.

    Is there a way that i can sort the arrayList on the start?
    Like that I want 1-4 before 3-2?


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    Super Moderator jps's Avatar
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    Default Re: How to sort this?

    7 - 7
    2 - 3
    7 - 5
    4 - 3
    4 - 2
    6 - 9
    4 - 6
    9 - 4
    3 - 5
    9 - 8
    5 - 4
    3 - 3

    Sort the set above on paper. Think about the steps taken to do so, and write them down. Know how to solve the problem before trying to solve the problem in code.

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    Default Re: How to sort this?

    Quote Originally Posted by Purple01 View Post
    ...So arrayList is full of these string1 things.
    Now start and end are both number.

    Is there a way that i can sort the arrayList on the start?
    Like that I want 1-4 before 3-2?
    One way would be to create a custom comparator and use Collections.sort. It could go like this:
        class CustomComparator implements Comparator<String>
        {
            @Override
            public int compare(String str1, String str2)
            {
                  //Code that extracts the integer values of substrings of str1 and str2
                  // Call them int1 and int2
                  // Return int1-int2
            }

    Then, call the Collections.sort function with your ArrayList<String> object like this:

            ArrayList<String> al = new ArrayList();
     
          //
          // Code to populate al goes here
          //
     
            System.out.println("Original: ");
            for (String str : al) {
                System.out.println("  " + str);
            }
     
            // For amusement, just sort by comparing strings
            Collections.sort(al);
            System.out.println("Natural sort of the Strings: ");
            for (String str : al) {
                System.out.println("  " + str);
            }
     
            // The real goal: Sort by numeric value of the first item in the "num1-num2" Strings
            Collections.sort(al, new CustomComparator());
            System.out.println("CustomComparator sort of the Strings: ");
            for (String str : al) {
                System.out.println("  " + str);
            }

    Example output
    Original: 
      1-10
      21-18
      25-4
      25-12
      1-9
      17-12
      10-16
      2-4
      17-13
      2-15
    Natural sort of the Strings: 
      1-10
      1-9
      10-16
      17-12
      17-13
      2-15
      2-4
      21-18
      25-12
      25-4
    CustomComparator sort of the Strings: 
      1-10
      1-9
      2-15
      2-4
      10-16
      17-12
      17-13
      21-18
      25-12
      25-4



    Cheers!

    Z
    Last edited by Zaphod_b; October 11th, 2012 at 10:51 AM.

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