Java 8 stream: replace single item in streamed collection

Question

I'm somewhat new to working in Java 8, and am refactoring some older code with (what appears to be a good use case for) a stream operation. The older code "works" but to my eyes it looks really inefficient.

The short version of my question is that I'm trying to find a single element of a List and replace it with an updated version of that same element (the key is the same, but properties have different values each time the code is called).

     try
     {
        List<Object> items = lookup(itemCache.getKey());
        for (int i = 0; i < items.size(); i++)
        {
           Object originalObject = items.get(i);
           if (originalObject.getPropValue() == newObject.getPropValue())
           {
              List<Object> newItems = new ArrayList<>(items);
              newItems.set(i, newObject);
              putIntoCache(newObject.getKey(), newItems);
              break;
           }
        }
     } 

     catch (Exception ex) { /*exception handling*/ }

Based on what I've read about streams thus far, it seems that I need to use a .map() or .filter() to isolate the element I want to identify, but that also seems like operations occurring after either filter or map in the stream statement would be operating on either not the full List or on a List where every item is affected by the .map().

It seems simple, but I am struggling to wrap my head around it. Because the initial lookup is a List itself, I was thinking the stream could replace all of this. The ArrayList<>() appears in the original code, but ordering of the items isn't important so long as I am able to replace that item by its key.

If you choose to help, thank you.

Answer 1

You can simply do:

List<Object> newItems = items.stream()
    .map(o -> o.getPropValue() == newObject.getPropValue() ? newObject : o)
    .collect(toList());
putIntoCache(newObject.getKey(), newItems);