Terminal operations

Terminal operations act as the trigger point in a pipelined stream operation to trigger execution. Terminal operations either return a void or a non-stream type object and once the pipelined operations have been executed on the stream, the stream becomes redundant. A Terminal operation is always required for a pipelined stream operation to be executed.

Stream operations can further be classified as short-circuiting operations. An intermediate operation is said to be short circuited when an infinite input produces a finite stream such as in the case of the limit() method. Similarly, short circuiting operations in the case of terminal operations is when an infinite input may terminate in finite time, as is the case for the methods anyMatch(), findAny(), and so on.

Streams also support parallelism , but in the case of stateful operations, since each parallel operation can have its own state, a parallel stateful operation may have to undergo multiple passes to complete the operation. For example, the distinct() method will not produce the correct results if the results are processed parallel in one go. However, no such restriction of multiple passes exists for stateless operations. The entire set of operations remains the same for both serial and parallel execution, only differentiator being the stream itself. If the Stream is parallel the operation will happen in parallel, or else the operations take place serially. The streams API provides a helper method, isParallel(), to check if the stream is serial or parallel. The only pre-condition that is required for a parallel stream operation to match that of the serial stream is the values passed to the operation must be non-interfering , where non-interfering is defined as the data whose underlying value does not change for any given set of operations.

The order of data in a stream can be dependent upon the source, intermediate operation, or the terminal operation.