Java Holiday Calendar 2016 (Day 21): Concatenate Java Streams
Merging your streams through concatenation can allow one stream to lazily consume others, saving you time and making your code more efficient.
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Today's tip is about concatenating streams. The task of the day is to construct a concatenated stream that lazily consumes a number of underlying streams. So, dumping the content from the various streams into a List and then streaming from the list or using the Stream.builder() will not do.
As an example, we have three streams with words that are relevant to US history and its Constitution:
// From 1787 final Stream preamble = Stream.of( "We", "the", "people", "of", "the", "United", "States" ); // From 1789 final Stream firstAmendment = Stream.of( "Congress", "shall", "make", "no", "law", "respecting", "an", "establishment", "of", "religion" ); // From more recent days final Stream epilogue = Stream.of( "In", "reason", "we", "trust" );
Creating a concatenated stream can be done in many ways including these:
// Works for a small number of streams Stream.concat( preamble, Stream.concat(firstAmendment, epilogue) ) .forEach(System.out::println); // Works for any number of streams Stream.of(preamble, firstAmendment, epilogue) .flatMap(Function.identity()) .forEach(System.out::println);
Both methods will produce the same result, and they will also close the underlying streams upon completion. Personally, I prefer the latter method, since it is more general and can concatenate any number of streams. This is the output of the program:
We the people of the United States Congress shall make no law respecting an establishment of religion In reason we trust
Follow the Java Holiday Calendar 2016 with small tips and tricks all the way through the winter holiday season.
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