Java 8 how to simplify for loop with lambda expressions

Question

I have this method in my code and need o simplify and reduce lines by using java 8 expressions. Lambda can be used for this but it seems impossible without a list as input.

  public ResourceUsage[] filterResourceUsages(ResourceUsage[] resourceUsages, int role, int includeResourceType)
    throws SpiderException
  {
    ArrayList<ResourceUsage> filteredResourceUsages = new ArrayList<>();

    String[] ids = new String[resourceUsages.length];
    for (int i = 0; i < resourceUsages.length; i++)
    {
      ids[i] = resourceUsages[i].resource;
    }

    ResourceData[] resourceData = resourceToolkitAdapter.getData(ids);

    for (int i = 0; i < resourceData.length; i++)
    {
      if (resourceUsages[i].role == role && resourceData[i].basic.type == includeResourceType)
      {
        filteredResourceUsages.add(resourceUsages[i]);
      }
    }
    return filteredResourceUsages.toArray(new ResourceUsage[filteredResourceUsages.size()]);
  }

I have tried using resourceUsages.forEach(resourceUsages.resource-> do something); but without list as input it seems impossible.

Is there any way to simplify this code?

"without list as input it seems impossible" ... Arrays.stream(myArray) — Michael
– Michael, Commented Aug 3, 2020 at 11:53
final List<String> ids = resourceUsages.stream().map(e -> e.resource).collect(toList()); — msfoster
– msfoster, Commented Aug 3, 2020 at 11:56

Wai Ha Lee · Accepted Answer · 2020-08-03 19:51:41Z

here is the origin arrays and batch solution:

public ResourceUsage[] filterResourceUsages(ResourceUsage[] resourceUsages, int role, int includeResourceType)
        throws SpiderException {

    String[] ids = Stream.of(resourceUsages)
            .map(ResourceUsage::getResource)
            .toArray(String[]::new);
    Map<String, ResourceData> resourceDataMap = Stream.of(resourceToolkitAdapter.getData(ids))
            .collect(Collectors.toMap(ResourceData::id, Function.identity()));
    return Stream.of(resourceUsages)
            .filter(usage -> usage.role == usage)
            .filter(resourceDataMap::containsKey)
            .filter(usage -> resourceDataMap.get(usage.resource).basic.type == includeResourceType)
            .toArray(ResourceUsage[]::new);
}

bhuwan · Accepted Answer · 2020-08-03 12:00:52Z

3

You can do like this with arrays

Arrays.stream(resourceUsages) 
            .forEach(e->System.out.print(e));

answered Aug 3, 2020 at 12:00

bhuwan

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Comments

Matthew · Accepted Answer · 2020-08-03 11:58:27Z

It's best if you use List<ResourceUsage> rather than arrays.

I'm also going to pretend it's ok to call resourceToolkitAdapter.getData() on each resource in turn, rather than in bulk.

The result will be something like so:

    public List<ResourceUsage> filterResourceUsages(List<ResourceUsage> resourceUsages, int role, int includeResourceType)
            throws SpiderException
    {
        return resourceUsages.stream()
                .filter(r->r.role == role)
                .filter(r->resourceToolkitAdapter.getData(r.resource).basic.type == includeResourceType)
                .collect(Collectors.toList());
    }

Ackdari · Accepted Answer · 2020-08-03 12:23:03Z

Opposed to the answer of Matthew, I assume that resourceToolkitAdapter.getData() should be called with a batch of ids.

public ResourceUsage[] filterResourceUsages(ResourceUsage[] resourceUsages, int role, int includeResourceType)
  throws SpiderException
{
  ResourceData[] resourceData = resourceToolkitAdapter.getData(
    Arrays.stream(resourceUsages)
      .map(r -> r.resource)
      .toArray(String[]::new)
  );

  return IntStream
    .range(0, resourceData.length)
    .filter(i -> resourceUsages[i].role == role )
    .filter(i -> resourceData[i].basic.type == includeResourceType)
    .mapToObj(i -> resourceUsages[i])
    .toArray(ResourceUsage[]::new);
}

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