How to sort a list of lists

[Sneha Kashyap]

Hi,
I am trying to sort a list of lists

 
List<List<String>> listOfLists=new ArrayList<List<String>>();  
 

the data in the list is something like this
{[def,ghi,xml],
[abc,ghi,cde],
[cat,ghi,der]}
I want the data to be
{[abc,ghi,cde],
[cat,ghi,der],
[def,ghi,xml],}
I am not able to use Collections.sort(listOfLists)
Any help is greatly appreciated.
Thanks in advance.

[Christophe Verré]

You have to tell the Collections how you want this list to be sorted. What about making a Comparator<List<String>> ?

[Sneha Kashyap]

Thanks
Hey can you please help me with some sample code.

[Campbell Ritchie]

Sneha Kashyap wrote:Thanks
Hey can you please help me with some sample code.

No. We believe people learn better if they show us what ideas they have first.

Write whatever you have: if you have no code, write down in small words how to sort your list of lists. Note this text with the lines is full of small words.

[Istvan Kovacs]

Since you want to sort the lists based on the 1st String they contain (at least, this is my understanding), have a class implement Comparator<List<String>> as Christophe has suggested, in its

public compare(List<String> one, List<String> other) {...}

method extract the 1st item from each list, and (since Strings are Comparable) just invoke

stringFromOne.compareTo(stringFromOther);

Be sure to handle the case when either of the lists is empty.
Pseudo-code:

int compareListsOfStrings(oneList, otherList) {
  if (oneList is empty || otherList is empty) {
    result = // it depends on how you want to handle this, you did not specify in your question
  } else {
    stringFromOne = oneList.firstString;
    stringFromOther = otherList.firstString;
    result = stringFromOne.compareTo(stringFromOther);
  }
  return result;
}

[Rob Spoor]

Given two List<String> objects the main question is indeed how they should be compared. The following is an often used algorithm (pseudo code):

while (both lists have more elements)
{
    get the next element from both lists
    compare these two elements
    if they are different return the comparison
}
// all elements checked are the same
// list1 has no more elements, list2 has no more elements, or both; check these cases
if (list1 has more elements) // list2 does not so list2 is the head of list1
{
    return 1; // to indicate list1 is "larger" than list2
}
// list1 has no more elements, check list2
if (list2 has more elements ) // list1 does not so list1 is the head of list2
{
    return -1; // to indicate list1 is "smaller" than list2
}
// list1 and list2 have no more elements so they are equal
return 0;