Querying ArrayList

jameswest

Hi just wondering if there's a way to query an array list short of iterating through all and flagging something?

I wanted to check if ALL objects in an array list had a flag set to true.. kind of like a reduce map or in C# .Any query?

GoToLoop

Although PDE is using Java 8, the way it is currently set up, latest functional syntaxes aren't allowed! =((

We'd need to write them on some other IDE for it. Otherwise we'd be allowed to use Collection::stream() & invoke Stream::allMatch() passing a Predicate as its argument using Java 8's lambda thin arrow operator ->: :-<

1. http://docs.Oracle.com/javase/8/docs/api/java/util/Collection.html#stream--
2. http://docs.Oracle.com/javase/8/docs/api/java/util/stream/Stream.html#allMatch-java.util.function.Predicate-
3. http://docs.Oracle.com/javase/8/docs/api/java/util/function/Predicate.html

Anyways, here's some archaic Java mock approach for it: :(|)

// forum.Processing.org/two/discussion/21761/querying-arraylist#Item_1
// GoToLoop 2017-Apr-02

import java.util.Collection;
import java.util.List;

int qty = (int) random(1, 6);
final List<Flag> flags = new ArrayList(qty);

void setup() {
  for (int i = 0; i++ < qty; )  flags.add(new Flag());
  println(flags);
  println(areAllTrue(flags));
  exit();
}

static final boolean areAllTrue(final Collection<Flag> elems) {
  for (final Flag f : elems)  if (!f.flag)  return false;
  return true;
}

class Flag {
  boolean flag = random(1) > .2;

  @ Override String toString() {
    return str(flag);
  }
}

GoToLoop

But in the end, I've managed to use Stream::allMatch(), by instantiating my own Predicate & implementing its abstract method test(). \m/

However, it's not as good as an actual lambda -> expression, which isn't bound to a specific datatype, escaping somehow from Java's brutal strongly typed system. O:-)

// forum.Processing.org/two/discussion/21761/querying-arraylist#Item_2
// GoToLoop 2017-Apr-02

import java.util.List;
import java.util.function.Predicate;

static final Predicate<Flag> FLAG = new Predicate<Flag>() {
  @ Override final boolean test(final Flag f) {
    return f.flag;
  }
};

int qty = (int) random(1, 6);
final List<Flag> flags = new ArrayList(qty);

void setup() {
  for (int i = 0; i++ < qty; )  flags.add(new Flag());
  println(flags);
  println(flags.stream().allMatch(FLAG));
  exit();
}

class Flag {
  boolean flag = random(1) > .2;

  @ Override String toString() {
    return str(flag);
  }
}

Another approach, besides using another IDE for a full Java 8 syntax, is implementing a function under Java's builtin JS language called Nashorn, and invoking it from Java's side, passing your Collection container as its argument. :ar!

After all in JS, all of its functions act like lambdas. And they can be passed freely as argument for another function, becoming callbacks for the receiving function! :-bd