Stream confusion

[Nathan Reynolds]

It is not only deterministic but also JIT (or an advanced version) could
reduce this code to the following single line in main().

System.out.println("Total red weight = 123");

Since there are no assignments to the Widget fields after construction,
they are effectively final.  I wouldn't be surprised if JIT assumes that
they are final.  Also, there is no need to put final in the main() body
since these values are effectively final.  (You can lookup effectively
final.)

I feel like you might be confusing final with deterministic.  Final
requires the value to not change.  Deterministic requires that a given
input always produces the same output.  The variables can change values
throughout the program's computation but the program will still be
deterministic if the same input gives the same output.  A nondeterministic
program would use SecureRandom.next___() or some other truly random source
during its computation.

On Wed, Nov 22, 2023 at 8:25 AM Archie Cobbs <archie.cobbs at gmail.com> wrote:

> Argh, sorry I pasted the wrong example. The Widget fields "color" and
> "weight" are supposed to NOT be final:
>
> @@ -5,8 +5,8 @@
>
>  public class Widget {
>
> -    private final Color color;
> -    private final int weight;
> +    private Color color;
> +    private int weight;
>
>      public Widget(Color color, int weight) {
>          this.color = color;
>
> The question remains the same - is the program deterministic?
>
> -Archie
>
> On Wed, Nov 22, 2023 at 10:06 AM Archie Cobbs <archie.cobbs at gmail.com>
> wrote:
>
>> I have an API design question about Streams, but instead of asking the
>> question outright I thought I'd ask it indirectly with a simple example.
>>
>> The Javadoc for Stream opens with this example:
>>
>>         int sum = widgets.stream()
>>                       .filter(w -> w.getColor() == RED)
>>                       .mapToInt(w -> w.getWeight())
>>                       .sum();
>>
>> OK, looks reasonable - we're computing the sum of the weights of all the
>> red widgets.
>>
>> Here's the question: Is the following program deterministic?
>>
>> import java.awt.*;
>> import java.util.function.*;
>> import java.util.stream.*;
>> import static java.awt.Color.*;
>>
>> public class Widget {
>>
>>     private final Color color;
>>     private final int weight;
>>
>>     public Widget(Color color, int weight) {
>>         this.color = color;
>>         this.weight = weight;
>>     }
>>
>>     public Color getColor() {
>>         return this.color;
>>     }
>>
>>     public int getWeight() {
>>         return this.weight;
>>     }
>>
>>     public static int totalRedWeight(Widget... widgets) {
>>         return Stream.of(widgets)
>>                 .filter(w -> w.getColor() == RED)
>>                 .mapToInt(w -> w.getWeight())
>>                 .sum();
>>     }
>>
>> // Test method
>>
>>     public static void main(String[] args) {
>>         final Widget w1 = new Widget(RED, 123);
>>         final Widget w2 = new Widget(BLUE, 456);
>>         final int total = Widget.totalRedWeight(w1, w2);
>>         System.out.println("Total red weight = " + total);
>>     }
>> }
>>
>> -Archie
>>
>> --
>> Archie L. Cobbs
>>
>
>
> --
> Archie L. Cobbs
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/amber-dev/attachments/20231122/8f57e24d/attachment-0001.htm>