Java 8 Applying stream filter based on a condition

Umar :

In Java 8, is there a way to apply the filter on a stream based on a condition,

example

I have this stream

if (isAccessDisplayEnabled) {
     src = (List < Source > ) sourceMeta.getAllSources.parallelStream()
         .filter(k - > isAccessDisplayEnabled((Source) k))
         .filter(k - > containsAll((Source) k, substrings, searchString))
         .collect(Collectors.toList());
 } else {
     src = (List < Source > ) sourceMeta.getAllSources.parallelStream()
         .filter(k - > containsAll((Source) k, substrings, searchString))
         .collect(Collectors.toList());
 }

I am adding the filter

.filter(k - > isAccessDisplayEnabled((Source) k)))

on the stream based on the if-else condition. Is there a way to avoid that if-else, since if there are more filters coming up,then it will be hard to maintain.

Please let me know

Holger :

One way to do it is

Stream<Source> stream = sourceMeta.getAllSources.parallelStream().map(x -> (Source)x);
if(isAccessDisplayEnabled) stream = stream.filter(s -> isAccessDisplayEnabled(s));
src = stream.filter(s - > containsAll(s, substrings, searchString))
            .collect(Collectors.toList());

another

 src = sourceMeta.getAllSources.parallelStream().map(x -> (Source)x)
     .filter(isAccessDisplayEnabled? s - > isAccessDisplayEnabled(s): s -> true)
     .filter(s - > containsAll(s, substrings, searchString))
     .collect(Collectors.toList());

In either case, note how performing one type cast at the beginning simplifies the entire stream pipline.

Both solutions avoid re-evaluating isAccessDisplayEnabled for every stream element, however, the second relies on the JVM’s capability of inlining s -> true when this code turns out to be performance critical.