Can streams in Java be reused?

Streams in Java cannot be reused once they are consumed. After a terminal operation, such as forEach(), collect(), or reduce(), is performed on a stream, the stream is considered closed and cannot be used again. Attempting to reuse a consumed stream will result in an IllegalStateException. This is because streams are designed to be single-use, allowing for efficient data processing and resource management.

If you need to process the same data multiple times, you will need to create a new stream from the original data source. For example, if you have a list of numbers and want to apply different processing steps, you would need to create a new stream for each processing step. Alternatively, you can collect the results of the first stream into a collection, such as a list, and then create a new stream from that collection for further processing.

The single-use nature of streams emphasizes the importance of carefully planning the operations you want to perform. By understanding that streams cannot be reused, developers can design their data processing pipelines to be efficient and effective, ensuring that each stream is used to its fullest potential before it is consumed. This design principle helps maintain the functional and declarative nature of the Stream API, making it a powerful tool for processing data in Java.