I would like to compare to streams, and check if they have 1 or more elements in common (finding 1 is sufficient to stop looking for more). I want to be able to apply this to Streams containing a custom-created class.
For illustration, let's say I have a class that looks like:
public class Point {
public final int row;
public final int col;
public Point(int row, int col) {
this.row = row;
this.col = col;
}
@Override
public boolean equals(Object obj) {
if (obj == null) return false;
if (obj.getClass() != this.getClass()) return false;
final Point other = (Point) obj;
return this.row == other.row && this.col == other.col;
}
@Override
public int hashCode() {
return Objects.hash(row, col);
}
}
And then I have two lovely streams that look like:
Stream<Point> streamA = Stream.of(new Point(2, 5), new Point(3, 1));
Stream<Point> streamB = Stream.of(new Point(7, 3), new Point(3, 1));
Given that these Streams have 1 Point in common (namely, Point(3, 1)), I would want the final result to be true.
The desired functionality can be pictured as:
public static boolean haveSomethingInCommon(Stream<Point> a, Stream<Point> b){
//Code that compares a and b and returns true if they have at least 1 element in common
}
Without collecting the two streams independently, you can group and identify if multiple values are mapped to any key.
public static boolean haveSomethingInCommon(Stream<Coord> a, Stream<Coord> b) {
return Stream.concat(a, b)
.collect(Collectors.groupingBy(Function.identity()))
.values().stream()
.anyMatch(l -> l.size() > 1);
}
If the same stream can have the same element twice or more, you can change the code to use -
Stream.concat(a.distinct(), b.distinct())
First of all you have to convert your Streams to a Set or List to not get the famous error:
java.lang.IllegalStateException: stream has already been operated upon or closed
And then you can use anyMatch as this:
public static boolean haveSomethingInCommon(Stream<Coord> a, Stream<Coord> b) {
Set<Coord> setA = a.collect(Collectors.toSet());
Set<Coord> setB = b.collect(Collectors.toSet());
return setA.stream().anyMatch(setB::contains);
}
Or you can convert only the b Stream to a Set and use:
public static boolean haveSomethingInCommon(Stream<Coord> a, Stream<Coord> b) {
Set<Coord> setB = b.collect(Collectors.toSet());
return a.anyMatch(setB::contains);
}
I would recommend to Set<Coord> instead of Stream<Coord> as param in your method.
public static boolean haveSomethingInCommon(Set<Coord> a, Set<Coord> b) {
return a.stream().anyMatch(b::contains);
}
there is a function disjoint in Collections:
public static boolean haveSomethingInCommon( Stream<Coord> a, Stream<Coord> b ) {
return( ! Collections.disjoint( a.collect( toList() ), b.collect( toList() ) ) );
}