Sorting alphanumeric strings java

Question

I have this array storing the suffix of some URLs the user is adding:

[U2, U3, U1, U5, U8, U4, U7, U6]

When I do this:

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Answer 1

I decide to use the idea @Abu gave, but I adapted it:

1. I check the ids of the urls the user is trying to add,
2. I remove the alphabetic suffix in this id and then I create an ArrayList to store the numerical part of each id.

3. I sort this ArrayList like @Abu taught me in his answer and then I verify for each id in this sorted ArrayList in the sequence it should be added..

   ArrayList <Integer> urlSorted = new ArrayList<Integer>();
   //sort the url ids
   for (Map<String, String> map : getUrlAttachments()) {
       String tmpId = map.get("id");
       if (tmpId.charAt(0) == 'U') {
           //gets the id, removing the prefix 'U'
           urlSorted.add( Integer.valueOf(tmpId.substring(1)));
       }
   }
   //sort the urlIds to check the sequence they must be added
   Collections.sort(urlSorted);
   //checks for each url id, compares if it's on the natural order of sorting to be added.
   for(Integer urlId: urlSorted) {
       for (Map<String, String> map : getUrlAttachments()) {
           String sortedId = "U"+urlId;
           String tmpId = map.get("id");
           //compare the ids to add the 1, then 2, then 3...
           if (map.get("id").equals(sortedId)) {
                       //code to save according to the sorted ids.
           }
        }
   }
   

Answer 2

Just use Collections.sort() method after creating an ArrayList of your values like this:

ArrayList<String> a = new ArrayList<String>();
a.add("U2");
a.add("U1");
a.add("U5");
a.add("U4");
a.add("U3");
System.out.println("Before : "+a);
Collections.sort(a);
System.out.println("After : "+a);

Output :

Before : [U2, U1, U5, U4, U3]
After : [U1, U2, U3, U4, U5]

Answer 3

I think what you are asking is similar to this one :

http://www.davekoelle.com/alphanum.html

You can break string into pure string and numeric string. for e.g: abc123 would be split into "abc" and "123" You can compare alphabetic string with normal comparison and then to sort "123" such kind of strings, you have two options: 1: Convert it into Integer and then compare 2: If number does not fit in Integer range, you can compare letter by letter.

for eg "123" vs "133" compare "1" and "1" = equal Compare "2" and "3" = greater so "123" < "133".

Option 2 is more accurate and less error proof.

Answer 4

Create a custom Comparator<Map<String,String>>:

public class IdComparator implements Comparator<Map<String,String>> {
  public int compare(Map<String,String> left, Map<String,String> right) {
    return orderKey(left).compareTo(orderKey(right));
  }
  static Integer orderKey(Map<String,String> m) { 
    return Integer.parseInt(m.get("id").substring(1)); 
  }
}

and then use Arrays.sort(urlAttachments, new IdComparator()); prior to iterating over it. Depending on details, you may push this sorting logic into getUrlAttachments() and keep the code you have posted exactly as it is now.