CODEWITHSUNDEEP
java
AC25
AC25

Reputation: 423

Replace for loop with a stream

I am more famiiliar with c# and linq but I have to work on some java code, so for the sake of learning and refactoring I was wondering if I can replace a for loop that Im using twice with a stream. I have a collection with a class object and then looping thru that collection and calling a function in that class. A few lines later I am doing the same thing just callinga different function. Looking at it and with my very new and limited knoweledge of java streams I was wondering if I can refactor a bit a la linq and pull the class object and just call the function

  Collection<RowProcessingHandler> rowHandlers = getRowHandlers();
    for (RowProcessingHandler handler : rowHandlers) {
        handler.onProcessingStarting(columnMap);
        handler.onProcess(dataList);
    }

Can I use a stream to get RowProcessingHandler handler and then I can just call onProcessingStarting(columnMap); and handler.onProcess(dataList); from a variable as so

 RowProcessingHandler handler = rowHandlers.stream().findFirst();

Which throws an error of Incompatible types

Upvotes: 1

Views: 123

Answers (1)

Stuck
Stuck

Reputation: 12292

You are doing fine, but the error originates from the fact that the stream API provides an Optional<T> as result from findFirst() because the stream potentially could be empty.

Optional<RowProcessingHandler> handlerOpt = rowHandlers.stream().findFirst();
if (handlerOpt.isPresent()) {
  RowProcessingHandler handler = handlerOpt.get()
}

or if you are sure that there is an entry in the stream you could do:

RowProcessingHandler handler = rowHandlers.stream().findFirst().orElseThrow();

depending on what you are about to do, this API might be more fluent:

rowHandlers.stream().forEach(handler => {
  handler.onProcessingStarting(columnMap);
  handler.onProcess(dataList);
});

Note that the scope of variables is a bit different in comparison to for-loops. If you use a variable within a stream scope (here for example columnMap) it must be effectively final.

Upvotes: 2

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