When Should You Use Parallel Streams in Java?

When should I use parallel streams in Java instead of regular streams?

myShapesCollection.parallelStream() // Example of a parallel stream
    .filter(e -> e.getColor() == Color.RED)
    .forEach(e -> System.out.println(e.getName()));

While Java 8 introduced parallel streams to easily leverage multi-core processors, it's important to consider when and how to use them effectively. Using parallel streams can improve performance for CPU-intensive operations but may not always offer benefits for every use case.

// Example of using parallelStream in Java
myShapesCollection.parallelStream()
    .filter(e -> e.getColor() == Color.RED)
    .forEach(e -> System.out.println(e.getName()));
// Regular stream for comparison
myShapesCollection.stream()
    .filter(e -> e.getColor() == Color.RED)
    .forEach(e -> System.out.println(e.getName()));

Causes

• Data Size: Parallel streams are beneficial when dealing with large datasets that can benefit from concurrent processing.
• CPU-Intensive Tasks: Operations requiring significant computation can see a performance boost from parallelization.
• Independent Operations: Each operation in the stream should be independent and not rely on previous results.

Solutions

• Use parallel streams for large data processing tasks when the operations are independent and the processing can be easily divided.
• Avoid using parallel streams for small datasets or simple operations where the overhead of managing threads outweighs the benefits.
• Consider the nature of the task: If tasks have side effects or rely on shared mutable state, prefer regular streams.

Mistake: Assuming parallel streams will always be faster without considering workload size.

Solution: Evaluate the data size and operation complexity before opting for parallel streams.

Mistake: Neglecting thread safety and mutable shared state when using parallel streams.

Solution: Ensure operations are stateless and thread-safe.

Mistake: Using parallel streams on small collections.

Solution: Use regular streams for smaller datasets.