排序arrayLists

Question

I have a scenario where I have two ArrayLists

ArrayList<String> sortedArrayList
ArrayList<String> unSortedArrayList

I have to sort unSortedArrayList depending on the sortedArrayList.

ie, sortedArrayList is already sorted, now based on sortedArrayList, I have to sort unSortedArrayList.

unSortedArrayList size is <= to the size of sortedArrayList.

Is there a Java API for that?

Any help is appreciated.

Answer 1

Using Google Guava 's excellent Ordering class:

Collections.sort(unSortedArrayList, Ordering.explicit(sortedArrayList));

EDIT You can also do

List<whatever> sortedList = Ordering.explicit(sortedArrayList).immutableSortedCopy(unsortedArrayList);

Answer 2

As I understand what you have is that each element in list 1 has a corresponding element in list 2, and you want list 2 sorted into the order of the 'corresponding' elements. Your best approach is to create an object to contain both Strings:

class StringPair {
  String s1;
  String s2;
}

Now make an array list of StringPairs and sort it based on the value of s1.

Answer 3

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

        for(String currentSortedStr:sortedList){

            if(unsortedList.size==0)break;

            if(unsortedList.remove(currentSortedStr)){
                newSortedList.add(currentSortedStr);
            }
        }

You can do something like this if you mean what @Sam Dufel says in the comment

As far as I know there is not such API method for this case.

This is not gonna take care of duplicates. remove will remove only the first occurence of that object. At the if the unsorted list size is greater than 0, you can say it contains duplicates. And if you need duplicates as well, you may wanna add some code to handle that case as well.

or if you mean the normal sorting;

Collections.sort(List<T>) will do the sorting for you.

Another way of doing it;

Collections.sort(unsortedList,new CustomComparator(sortedList));

public class CustomComparator implements Comparator<String>{
        private List<String> sortedList;
        public CustomComparator(List<String> sortedList){
            this.sortedList = sortedList;
        }

        @Override
        public int compare(String o1, String o2) {
            return sortedList.indexOf(o1)-sortedList.indexOf(o2);
        }       
    }

Answer 4

Although your question is not clear enough I think that the following will help you.

You can use Collections.sort() to sort list. If you need some custom modification to sort mechanism implement your own Comparator and use 2 args version of this method: Collections.sort(list, comparable)