[COLLECTIONS-747] MultiKey.getKeys class cast exception

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.4
• Fix Version/s: 4.5.0-M1
• Component/s: KeyValue
• Assignee: Gary D. Gregory
• Reporter: Walter Laan
• Created: 10/Feb/20 14:49
• Updated: 17/Feb/20 09:00
• Resolved: 16/Feb/20 21:28

Description

When using an non-array constructor of MultiKey, an Object[] is created, which cannot be cast to a K[]

import org.apache.commons.collections4.keyvalue.MultiKey;

public class MultiKeyClassCastException {

    public static void main(String[] args) {
        MultiKeyClassCastException key1 = new MultiKeyClassCastException();
        MultiKeyClassCastException key2 = new MultiKeyClassCastException();
        MultiKeyClassCastException[] keys = new MultiKey<>(key1, key2).getKeys();
    }
}

// running gives (same error if in module):

Exception in thread "main" java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [LMultiKeyClassCastException; ([Ljava.lang.Object; is in module java.base of loader 'bootstrap'; [LMultiKeyClassCastException; is in unnamed module of loader 'app')
	at MultiKeyClassCastException.main(MultiKeyClassCastException.java:8)

AFAIK, the only way to fix this (with source compatibility), is to only have a varargs constructors. but I think this breaks binary compatibility though and cannot be used with the existing constructors.

    @SafeVarargs
    public MultiKey(K... keys) {
        this.keys = keys;
    }

Workaround is to use array constructor with correct typed array or

Object[] keys = multiKey.getKeys();

explicitly.