What accumulates the Java equivalent of C ++ or Groovy?

Question

Essentially, I would like to do the following as a single line:

int sum = initialValue; for (int n : collectionOfInts) { sum += n; } return sum; 

I see that there is http://functionaljava.org/examples/1.5/#Array.foldLeft , but I do not need to copy the collection.

Answer 1

I see that there is http://functionaljava.org/examples/1.5/#Array.foldLeft , but I do not need to copy the collection.

If you use foldLeft from IterableW instead of Array, you won’t have to copy anything.

Answer 2

Sorry, it still does not exist in Java 7. You will have to wait for Java 8, where Closures should be implemented.

At the same time, you can use FunctionalJava, Guava, or a JVM-compatible language with closing enabled, such as Groovy.

Answer 3

Just for fun, here's how to do it without an external library:

 return fold(collectionOfInts, 0, ADD); 

Oh, and the rest :)

 static <X, Y> X fold(final Iterable<? extends Y> gen, final X initial, final Function2<? super X, ? super Y, ? extends X> function) { final Iterator<? extends Y> it = gen.iterator(); if (!it.hasNext()) { return initial; } X acc = initial; while (it.hasNext()) { acc = function.apply(acc, it.next()); } return acc; } static final Function2<Integer, Integer, Integer> ADD = new Function2<Integer, Integer, Integer>() { @Override public Integer apply(Integer a, Integer b) { return a + b; } }; interface Function2<A, B, C> { C apply(A a, B b); }