Order of Intermediate Operations The order of intermediate operations in a stream pipeline can impact the performance of a stream pipeline. If intermediate operations that reduce the size of the stream can be performed earlier in the pipeline, fewer elements need to be processed by the subsequent operations. Moving intermediate operations such as filter(), distinct(), […]
Streams from Collections The default methods stream() and parallelStream() of the Collection interface create streams with collections as the data source. Collections are the only data source that provide the parallelStream() method to create a parallel stream directly. Otherwise, the parallel() intermediate operation must be used in the stream pipeline. The following default methods for […]
Concatenating Streams The concat() method creates a resulting stream where the elements from the first argument stream are followed by the elements from the second argument stream. The code below illustrates this operation for two unordered sequential streams. Two sets are created at (1) and (2) based on lists of strings that are passed to […]
Setting a Stream as Unordered The unordered() intermediate operation does not actually reorder the elements in the stream to make them unordered. It just removes the ordered constraint on a stream if this constraint is set for the stream, indicating that stream operations can choose to ignore its encounter order. Indicating the stream to be […]
Summary of Stream Building Methods Selected methods for building streams from various data sources are listed in Table 16.1. The first column lists the method names and the reference type that provides them. For brevity, the parameters of the methods are omitted. Note that some methods are overloaded. The prefix NumType stands for Int, Long, […]
Streams from Factory Methods in the Files Class A detailed discussion of the NIO2 File API that provides the classes for creating the various streams for reading files, finding files, and walking directories in the file system can be found in Chapter 21, p. 1285. Analogous to the lines() method in the BufferedReader class, a […]
Streams from Arrays We have seen examples of creating streams from arrays when discussing the variable arity of() method of the stream interfaces and the overloaded Arrays.stream() methods earlier in the chapter (p. 893). The sequential stream created from an array has the same order as the positional order of the elements in the array. […]
The Empty Stream An empty stream can be obtained by calling the empty() method of the core stream interfaces. As the name implies, such a stream has no elements. Click here to view code image Stream<CD> cdStream = Stream.empty(); // Empty stream of CD.System.out.println(“Count: ” + cdStream.count()); // Count: 0IntStream iStream = IntStream.empty(); // Empty […]
Streams from a BufferedReader A BufferedReader allows contents of a text file to be read as lines. A line is a sequence of characters terminated by a line terminator sequence. Details of using a Buffered-Reader are covered in ยง20.3, p. 1251. A simple example of creating streams on text files using a BufferedReader is presented […]
Taking and Dropping Elements Using Predicates Both the takeWhile() and the dropWhile() methods find the longest prefix of elements to take or drop from the input stream, respectively. The code below at (1) and (2) illustrates the case for ordered streams. The take-While() method takes odd numbers from the input stream until a number is […]
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