JAVA EE: Whether we can reuse the Stream or not | Java 8 streams

Tuesday 19 September 2017

Whether we can reuse the Stream or not | Java 8 streams | Streams in Java 8

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https://www.youtube.com/watch?v=6_6ytShUcJU&list=UUhwKlOVR041tngjerWxVccw

StreamDemo.java

import java.util.Optional;
import java.util.stream.Stream;

public class StreamDemo
{
    public static void main(String[] args)
    {

        Stream<String> stream = Stream.of("a", "b", "c");               

        Optional<String> anyElement = stream.findAny();

        System.out.println("anyElement = " + anyElement);

        /*
         * Attempt to reuse the same reference after calling the
         * terminal operation will trigger the IllegalStateException.
         * 
         * As the IllegalStateException is a RuntimeException, a
         * compiler will not signalize about a problem. So, it is very
         * important to remember that Java 8 streams can’t be reused.
         * 
         * This kind of behavior is logical because streams were
         * designed to provide an ability to apply a finite sequence
         * of operations to the source of elements in a functional
         * style, but not to store elements.
         */
        Optional<String> firstElement = stream.findFirst();
        System.out.println("firstElement = " + firstElement);
    }

}

Output

anyElement = Optional[a]
Exception in thread "main" java.lang.IllegalStateException: 
stream has already been operated upon or closed
    at java.util.stream.AbstractPipeline.evaluate(Unknown Source)
    at java.util.stream.ReferencePipeline.findFirst(Unknown Source)
    at StreamDemo.main(StreamDemo.java:28)