How to map multiple variable in Java lambda?

user_10787804 0
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I have a method that filters in a List containing enums i

if (availableImageSizes.stream()
                       .filter(t -> t.getNameSuffix().equals("-xs"))
                       .findFirst().isPresent())
{
    int width = availableImageSizes.stream()
                       .filter(t -> t.getNameSuffix().equals("-xs"))
                       .findFirst().getWidth();

    int height = availableImageSizes.stream()
                       .filter(t -> t.getNameSuffix().equals("-xs"))
                       .findFirst().getHeight();
}

As you see I try to filter the list according to its NameSuffix and after filtering I want to map that value's width and height to a variable. But the code is wrong and even if it works, it is so ugly.

Can I map multiple variable in one lambda? If so, how can I achieve this?

java-stream java-8 option-type lambda java
2 Answers

If you need the values as part of the method's return value

If there is a sensible default, I'd do it like this

Optional<ImageSize> xsImageSize = availableImageSizes.stream()
    .filter(t -> t.getNameSuffix().equals("-xs"))
    .findFirst();
int height = xsImageSize.map(ImageSize::getHeight).orElse(-1);
int width = xsImageSize.map(ImageSize::getWidth).orElse(-1);

Alternatively, nullable Integers

Integer height = xsImageSize.map(ImageSize::getHeight).orElse(null);
Integer width = xsImageSize.map(ImageSize::getWidth).orElse(null);

Otherwise

Optional<ImageSize> xsImageSize = availableImageSizes.stream()
    .filter(t -> t.getNameSuffix().equals("-xs"))
    .findFirst();
if (xsImageSize.isPresent())
{
    int height = xsImageSize.get().getHeight();
    int width = xsImageSize.get().getWidth();
    //...
}

If you don't need those values for the return

availableImageSizes.stream()
    .filter(t -> t.getNameSuffix().equals("-xs"))
    .findFirst()
    .ifPresent(imageSize -> {
        int height = imageSize.getHeight();
        int width = imageSize.getWidth();
        //...
    });

or

availableImageSizes.stream()
    .filter(t -> t.getNameSuffix().equals("-xs"))
    .findFirst()
    .ifPresent(this::processXsImageSize);

//...
private void processXsImageSize(ImageSize imageSize) {
    int height = imageSize.getHeight();
    int width = imageSize.getWidth();
    //...
}
user_18985630

First of all, your goal is to remove duplicated code:

availableImageSizes.stream()
                   .filter(t -> t.getNameSuffix().equals("-xs"))
                   .findFirst()

I am not sure what "in one lamba" means. However, you can achieve this with a single chain of Stream and Optional method calls. However, you are not able to retrun two or more values at once. The solution is to return either an array to be decomposed to width and height. In better case use a custom object Dimension/Point class or Pair/AbstractMap.SimpleEntry.

The arrays is the easiest way to show the solution.

Integer[] dimensions = availableImageSizes.stream()
    .filter(t -> t.getNameSuffix().equals("-xs"))                // images with a suffix
    .findFirst()                                                 // Optional<MyImage>
    .map(obj -> new Integer[] {obj.getWidth(), obj.getHeight()}) // map dimensions
    .orElse(new Integer[] {null, null});                         // else default values
        
Integer width = dimensions[0];                                   // destructured width
Integer height = dimensions[1];                                  // destructured height
user_37649650
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