[GROOVY-6146] Calling a Java vararg method from Groovy with a null argument cast to the vararg type behaves differently than in Java

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.1.2
• Fix Version/s: 5.0.0-alpha-1
• Component/s: groovy-runtime
• Labels: varargs
• Assignee: Eric Milles
• Reporter: David Tonhofer
• Created: 06/May/13 13:38
• Updated: 23/Aug/23 09:11
• Resolved: 15/Jul/23 22:09

Description

We have this Java class:

JavaReceiver.java

public class JavaReceiver {

    public static String receive(String... x) {
        String res = ((x == null) ? "null" : ("an array of size " + x.length));
        return "received 'x' is " + res;
    }
}

which is called from this Java class to verify various effect:

JavaSender.java

import org.junit.Test;

public class JavaSender {

    @Test
    public void sendNothing() {
        System.out.println("sendNothing(): " + JavaReceiver.receive());
    }

    @Test
    public void sendNullWithNoCast() {
        System.out.println("sendNullWithNoCast(): " + JavaReceiver.receive(null));
    }

    @Test
    public void sendNullWithCastToString() {
        System.out.println("sendNullWithCastToString(): " + JavaReceiver.receive((String)null));
    }

    @Test
    public void sendNullWithCastToArray() {
        System.out.println("sendNullWithCastToArray(): " + JavaReceiver.receive((String[])null));
    }

    @Test
    public void sendOneValue() {
        System.out.println("sendOneValue(): " + JavaReceiver.receive("a"));
    }

    @Test
    public void sendThreeValues() {
        System.out.println("sendThreeValues(): " + JavaReceiver.receive("a", "b", "c"));
    }
    
    @Test
    public void sendArray() {
        System.out.println("sendArray(): " + JavaReceiver.receive(new String[]{"a", "b", "c"}));
    }

}

Running the test above yields this output:

sendNothing(): received 'x' is an array of size 0
sendNullWithNoCast(): received 'x' is null
sendNullWithCastToString(): received 'x' is an array of size 1
sendNullWithCastToArray(): received 'x' is null
sendOneValue(): received 'x' is an array of size 1
sendThreeValues(): received 'x' is an array of size 3
sendArray(): received 'x' is an array of size 3

Using essentially similar code from Groovy:

GroovySender.groovy

import org.junit.Test

class GroovySender {

    @Test
    void sendNothing() {
        System.out << "sendNothing(): " << JavaReceiver.receive() << "\n"
    }

    @Test
    void sendNullWithNoCast() {
        System.out << "sendNullWithNoCast(): " << JavaReceiver.receive(null) << "\n"
    }

    @Test
    void sendNullWithCastToString() {
        System.out << "sendNullWithCastToString(): " << JavaReceiver.receive((String)null) << "\n"
    }

    @Test
    void sendNullWithCastToArray() {
        System.out << "sendNullWithCastToArray(): " << JavaReceiver.receive((String[])null) << "\n"
    }

    @Test
    void sendOneValue() {
        System.out << "sendOneValue(): " + JavaReceiver.receive("a") << "\n"
    }

    @Test
    void sendThreeValues() {
        System.out << "sendThreeValues(): " + JavaReceiver.receive("a", "b", "c") << "\n"
    }

    @Test
    void sendArray() {
        System.out << "sendArray(): " + JavaReceiver.receive( ["a", "b", "c"] as String[] ) << "\n"
    }
}

Yields the different output:

sendNothing(): received 'x' is an array of size 0
sendNullWithNoCast(): received 'x' is null
sendNullWithCastToString(): received 'x' is null
sendNullWithCastToArray(): received 'x' is null
sendOneValue(): received 'x' is an array of size 1
sendThreeValues(): received 'x' is an array of size 3
sendArray(): received 'x' is an array of size 3

So the "cast to a String" does not result in a call with the argument
"String[]

{null}

".

Maybe that is expected behaviour though.

Issue Links

• is duplicated by: GROOVY-10099 A single null argument to a varargs parameter is received as null
• is related to: GROOVY-1026 Null argument to methods with vararg parameters are replaced with array of length 1
• relates to: GROOVY-10722 AIC via array-based (variadic) constructor null and array arguments