JAVA EE: What will happen if we call terminal operation more than one time?

Thursday, 24 August 2017

What will happen if we call terminal operation more than one time? | Streams in Java 8

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What will happen if we call terminal operation more than one time? | Streams in Java 8

StreamDemo.java

import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;

public class StreamDemo
{
    public static void main(String[] args)
    {
        List<String> nameList = Arrays.asList("Peter", "Steve", "Juli");
        
        Stream<String> stream = nameList.stream();

        // perform terminal operation by forEach method
        stream.forEach(System.out::println);

        // the stream is already closed, so this code will throw
        // exception at runtime
        stream.forEach(System.out::print);

    }
}

Output

Peter
Steve
Juli
Exception in thread "main" java.lang.IllegalStateException: stream has already been operated upon or closed
    at java.util.stream.AbstractPipeline.sourceStageSpliterator(Unknown Source)
    at java.util.stream.ReferencePipeline$Head.forEach(Unknown Source)
    at StreamDemo.main(StreamDemo.java:18)