Unknown Source Java 10

Question

I am getting an error while running following code:

public class TestClass {

public static void main(String[] args) {
    var list = new ArrayList<String>();
    list.add("Harry");
    list.add("Marry");
    list.add(null);
    list.add("Larry");

    list.removeIf(e -> e.startsWith("H"));
    list.forEach(System.out::println);

    }
}

Getting following error:

Exception in thread "main" java.lang.NullPointerException
at test/test.TestClass.lambda$0(TestClass.java:14)
at java.base/java.util.ArrayList.removeIf(Unknown Source)
at java.base/java.util.ArrayList.removeIf(Unknown Source)
at test/test.TestClass.main(TestClass.java:14)

Why I am getting the unknow source error, it works fine if I provide following lambda:

list.removeIf(e -> e == null);

`.startsWith` doesn't work with `null` string. so you need to put condition there. — sinsuren, Jun 10 '18 at 18:20
the `Unknown Source` only means that there are no source files attached, i.e. the trace cannot determine which line (in a `.java` file) caused this `Exception`. The actual `Excpetion` is a `NullPointerException` — Turing85, Jun 10 '18 at 18:27

score 7 · Accepted Answer · edited Jul 02 '18 at 18:52

7

null.startsWith("H") returns NullPointerException instead you have to check if the value is null or not then use startsWith:

list.removeIf(e -> e != null && e.startsWith("H"));

edited Jul 02 '18 at 18:52

Jean-François Fabre

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answered Jun 10 '18 at 18:19

Youcef LAIDANI

55,661
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1

Yes. Thanks. It works now. – user2173372 Jun 10 '18 at 18:21

score 4 · Answer 2 · answered Jun 10 '18 at 18:20

4

One of your entries is null and e.startsWith("H") gives a NullPointerException

list.removeIf(e -> e != null && e.startsWith("H"));

answered Jun 10 '18 at 18:20

Yassin Hajaj

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Ousmane D. · Answer 3 · 2018-06-10T18:32:41.210

it works when you perform:

list.removeIf(e -> e == null);

because you're explicitly saying "remove all null elements", so there is no chance of NullPointerException here.

whereas:

 list.removeIf(e -> e.startsWith("H"));

is saying "remove all elements that start with 'H' " but if e is null then you're doomed as it will yield a NullPointerException.

Instead, check if it's not null prior to checking whether it starts with "Hi" or not.

list.removeIf(e -> e != null && e.startsWith("H"));

Unknown Source Java 10

3 Answers3