List comprehensions: Difference between revisions

=={{header|Java}}==

Java can stream a list, allowing something like a list comprehension. The syntax is (unsurprisingly) verbose, so you might wonder how good the likeness is. I've labeled the parts according to the description in Wikipedia.

Using list-of-arrays made the syntax easier than list-of-lists, but meant that you need the "output expression" part to get to something easily printable.

<lang Java>// Boilerplate

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class PythagComp{

public static void main(String[] args){

System.out.println(run(20));

}

static List<List<Integer>> run(int n){

return

// Here comes the list comprehension bit

// input list - bit clunky

new ArrayList<Integer[]>(){{

for(int x=1; x<n; x++)

for(int y=x; y<n; y++)

for(int z=y; z<n; z++)

add(new Integer[]{x,y,z});

}}.stream()

// predicate

.filter(a -> a[0]*a[0] + a[1]*a[1] == a[2]*a[2])

// output expression

.map(a -> Arrays.asList(a))

// the result is a list

.collect(Collectors.toList());

}

}

</lang>

{{Out}}

<pre>[[3, 4, 5], [5, 12, 13], [6, 8, 10], [8, 15, 17], [9, 12, 15]]</pre>