Convert a Object[] of booleans to a boolean[] using streams

Question

I can do the conversion with code like this:

Object[] array = (Object[]) message.get(key); boolean[] result = new boolean[array.length]; for (int i = 0; i < array.length; i++) {     result[i] = (boolean) array[i]; } 

But, I was think that is possible to do the same conversion using Java 8 streams. I start to code something like this:

boolean[] =  Arrays.stream(array)                    .map(Boolean.class::cast)                    .map(Boolean::booleanValue)                    .toArray() 

But this code doesn't work. Compiler says

incompatible types: java.lang.Object[] cannot be converted to boolean[] 

I'm trying to understand what is the problem with the code. I think that map(Boolean::booleanValue) would return a stream of boolean values I can collect with toArray.

Answer 1

No, because map(Boolean::booleanValue) expands to

map((Boolean value) -> (Boolean)value.booleanValue()); 

(note the autoboxing inserted by the compiler, because the function passed to map() has to return an Object, not a boolean)

This is why the Java8 streams include a whole bunch of specialized classes (IntStream, LongStream, and DoubleStream). Sadly, there is no specialized stream class for boolean.