Converting List<Integer> to List<String>

I have a list of integers, List<Integer> and I'd like to convert all the integer objects into Strings, thus finishing up with a new List<String>.

Naturally, I could create a new List<String> and loop through the list calling String.valueOf() for each integer, but I was wondering if there was a better (read: more automatic) way of doing it?

Solution 1:

Using Google Collections from Guava-Project, you could use the transform method in the Lists class

import com.google.common.collect.Lists;
import com.google.common.base.Functions

List<Integer> integers = Arrays.asList(1, 2, 3, 4);

List<String> strings = Lists.transform(integers, Functions.toStringFunction());

The List returned by transform is a view on the backing list - the transformation will be applied on each access to the transformed list.

Be aware that Functions.toStringFunction() will throw a NullPointerException when applied to null, so only use it if you are sure your list will not contain null.

Solution 2:

Solution for Java 8. A bit longer than the Guava one, but at least you don't have to install a library.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

//...

List<Integer> integers = Arrays.asList(1, 2, 3, 4);
List<String> strings = integers.stream().map(Object::toString)
                                        .collect(Collectors.toList());

For Java 11,

List<String> strings = integers.stream().map(Object::toString)
                                        .collect(Collectors.toUnmodifiableList());

Still no map convenience method, really?