Lambda Collector throwing java.lang.ArrayIndexOutOfBoundsException - java-8

Question

Lambda expression intermittently throws ArrayIndexOutOfBoundsException in my Impl.java class.
Stacktrace:
java.lang.ArrayIndexOutOfBoundsException: 1 java.lang.ArrayIndexOutOfBoundsException: 1
at Impl.lambda$retrieve$0(Impl.java:124) ~[classes/:?]
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_181]
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382) ~[?:1.8.0_181]
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) ~[?:1.8.0_181]
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[?:1.8.0_181]
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[?:1.8.0_181]
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:1.8.0_181]
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[?:1.8.0_181]
at Impl.retrieve(Impl.java:125) ~[classes/:?]
I've written a sample program simulating the scenario. But, in the sample program, it is NOT reproducible. However, can someone figure out any problem with the following code?
I've tried with empty/non-empty input. When I make numberStr to throw ArrayIndexOutOfBoundsException, the stack trace appears different:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at LambdaTest.lambda$0(LambdaTest.java:13)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at LambdaTest.main(LambdaTest.java:14)
Sample program:
import java.util.List;
import java.util.stream.Collectors;
import org.apache.commons.math3.util.Pair;
import com.google.common.collect.Lists;
public class LambdaTest {
public static void main(String[] args) {
String[] numberStr = { "one", "two", "three" };
List<Pair<String, SampleEnum>> result = getInputPairs().stream()
.map(entry -> new Pair<String, SampleEnum>(numberStr[entry.getFirst()], entry.getSecond()))
.collect(Collectors.toList()); // <=== similar to Impl.java:125
System.out.println("Lambda tested." + result.toString());
}
private static List<Pair<Integer, SampleEnum>> getInputPairs() {
List<Pair<Integer, SampleEnum>> pairs = Lists.newArrayList();
//pairs.add(new Pair<Integer, SampleEnum>(0, SampleEnum.ONE_AND_ONLY));
return pairs;
}
}
enum SampleEnum {
ONE_AND_ONLY
}
In what cases, can the expression fail? and how to fix it?

Answer 1

It looks like numberStr[entry.getFirst()] is throwing the error. In your Impl class, numberStr somehow has too few elements. Either use a debugger or put this before the .stream() line to see what's going on:
System.out.println("numberStr: " + Arrays.toString(numberStr));

Answer 2

On the same line as Sean mentioned
java.lang.ArrayIndexOutOfBoundsException: 1
This exception clearly tells the that while fetching the data from Array for 1st element, it failed.
If you fix this then it should work fine. To see more clearly, setup debugger at numberStr and see how many elements are there and check how many elements you get from stream. If you try to access an index which is not available in your array. You should see this exception