Let's say I have a list of objects implementing below interface:
public interface Summable<T> {
T add(T o1);
}
Let's say I have also some class which is able to sum these objects:
public class Calculator<T extends Summable<T>> {
public T sum(final List<T> objects) {
if (null == objects) {
throw new IllegalArgumentException("Ups, list of objects cannot be null!");
}
T resultObject = null;
for (T object : objects) {
resultObject = object.add(resultObject);
}
return resultObject;
}
}
How can I achieve the same using Java 8 streams?
I'm playing around a custom Collector, but couldn't figure out some neat solution.
Using Stream.collect() asList(1, 2, 3, 4, 5); Integer sum = integers. stream() . collect(Collectors. summingInt(Integer::intValue));
A simple solution to calculate the sum of all elements in a List is to convert it into IntStream and call sum() to get the sum of elements in the stream. There are several ways to get IntStream from Stream<Integer> using mapToInt() method.
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