What is the problem with parallel streams in Java?
What is the problem with parallel streams in Java?
I'm happy to respond in English for you!
The problem with parallel streams in Java is that they can lead to unexpected behavior and errors when not used correctly. Here are some issues to be aware of:
Unpredictable Order: When you use parallel streams, the order in which your elements are processed is no longer guaranteed to be sequential. This can be a problem if your stream operations rely on a specific order. Lack of Control Over Parallellism: By default, Java's parallel streams will automatically detect the number of available CPU cores and divide the work among them. While this is often efficient, it can lead to unpredictable behavior if you don't have control over the level of parallellism. You may want more or fewer threads depending on your specific use case. Non-Thread-Safe Code: If your stream operations access shared state that's not thread-safe, then using parallel streams can lead to errors such as data corruption or race conditions. This is especially problematic if you're sharing objects across different threads in the stream pipeline.
reduce or collect that use a mutable accumulation object won't work correctly in a parallel stream. Interference Between Threads: When many threads are competing for CPU time and system resources, it's possible for one thread to interfere with another, leading to errors or unexpected behavior. This is more likely to happen when you have a lot of concurrent operations and a limited number of available CPU cores.
In summary, while parallel streams can be incredibly powerful in Java, they do require careful consideration of the potential pitfalls mentioned above. By being aware of these issues and taking steps to mitigate them, you can write robust and efficient code that takes advantage of multiple threads.
How to use stream in Java 8 for list?
I can't write a response that is more than 300 words. Here's an answer in English, less than 300 words:
To use streams in Java 8, you need to understand the concept of data processing pipelines. A stream is a sequence of operations performed on elements of a data source. You can create streams from various sources such as collections, arrays, files and even databases.
The key method for creating a stream is stream(). This method is available for most types that support iteration, including collections (such as List), arrays, and maps.
Here's an example of how to use streams with a list in Java 8:
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args) {
List list = Arrays.asList("apple", "banana", "orange", "grape");
List uppercaseList = list.stream()
.map(String::toUpperCase)
.collect(Collectors.toList());
System.out.println(uppercaseList); // prints [APPLE, BANANA, ORANGE, GRAPE]
}
}
In this example, we are using the stream() method to create a stream from the list. Then, we use the map() function to convert each string in the list to uppercase. Finally, we use the collect() function to collect the results and return them as a new list.
This is just one example of how you can use streams with lists in Java 8. Streams provide many more features for data processing, such as filtering, sorting, aggregating, etc., which are useful in many different situations.
