Geek Answers Handbook

To check if all elements of the "stream" are identical

I'm trying to change some of my old code to take advantage of the functional aspects of Java 8. In particular, I am moving from using Guava predicates to java.util.function.Predicate. One predicate is to check if a is Streamhomogeneous, i.e. Consists of all the same elements.

In my old code (using Guava Predicate) I had this:

static <T> Predicate<Iterable<T>> isHomogeneous() {
    return new Predicate<Iterable<T>>() {
        public boolean apply(Iterable<T> iterable) {
            return Sets.newHashSet(iterable).size() == 1;
        }
    };
}

This is a new version using java.util.function.Predicate:

public static Predicate<Stream<?>> isHomogeneous =
    stream -> stream.collect(Collectors.toSet()).size() == 1;

The IDE (IntellijIDEA v.12) does not display a red squiggly line indicating an error, but when I try to compile, I get the following:

java: no suitable method found for
collect(java.util.stream.Collector<java.lang.Object,capture#1 of ?,java.util.Set<java.lang.Object>>)
  method java.util.stream.Stream.<R>collect(java.util.function.Supplier<R>,java.util.function.BiConsumer<R,? super capture#2 of ?>,java.util.function.BiConsumer<R,R>) is not applicable
    (cannot infer type-variable(s) R
      (actual and formal argument lists differ in length))
  method java.util.stream.Stream.<R,A>collect(java.util.stream.Collector<? super capture#2 of ?,A,R>) is not applicable
    (cannot infer type-variable(s) R,A,capture#3 of ?,T
      (argument mismatch; java.util.stream.Collector<capture#2 of ?,capture#4 of ?,java.util.Set<capture#2 of ?>> cannot be converted to java.util.stream.Collector<? super capture#2 of ?,capture#4 of ?,java.util.Set<capture#2 of ?>>))

: , , , . , , List<>. , isHomogeneous.

+4
2

- Stream.distinct , 1 .

stream.distinct().limit(2).count() == 1
+12

, ,

static <T> boolean isHomogeneous(Iterable<T> iterable) {
    return Sets.newHashSet(iterable).size() == 1;
}


Iterable<Integer> iterable1 = Lists.newArrayList(1, 1);
Iterable<Integer> iterable2 = Lists.newArrayList(1, 2);

Stream.of(iterable1, iterable2).filter(YourClass::isHomogeneous).collect(Collectors.toList());
-1

More articles:


All Articles