How to lowercase every element of a collection efficiently?

Question

What\'s the most efficient way to lower case every element of a List or Set?

My idea for a List:

final List strings = new ArrayList<         


        

Answer 1

I was looking for similar stuff, but was stuck because my ArrayList object was not declared as GENERIC and it was available as raw List type object from somewhere. I was just getting an ArrayList object "_products". So, what I did is mentioned below and it worked for me perfectly ::

List<String> dbProducts = _products;
    for(int i = 0; i<dbProducts.size(); i++) {
        dbProducts.add(dbProducts.get(i).toLowerCase());         
    }

That is, I first took my available _products and made a GENERIC list object (As I were getting only strings in same) then I applied the toLowerCase() method on list elements which was not working previously because of non-generic ArrayList object.

And the method toLowerCase() we are using here is of String class.

String java.lang.String.toLowerCase()

not of ArrayList or Object class.

Please correct if m wrong. Newbie in JAVA seeks guidance. :)

Answer 2

This is probably faster:

for(int i=0,l=strings.size();i<l;++i)
{
  strings.set(i, strings.get(i).toLowerCase());
}

Answer 3

Try CollectionUtils#transform in Commons Collections for an in-place solution, or Collections2#transform in Guava if you need a live view.

Answer 4

Yet another solution, but with Java 8 and above:

List<String> result = strings.stream()
                             .map(String::toLowerCase)
                             .collect(Collectors.toList());

Answer 5

Using JAVA 8 parallel stream it becomes faster

List<String> output= new ArrayList<>();
List<String> input= new ArrayList<>();
input.add("A");
input.add("B");
input.add("C");
input.add("D");
input.stream().parallel().map((item) -> item.toLowerCase())
            .collect(Collectors.toCollection(() -> output));