Interfaces:
interface PublicCloneable {
Object clone();
}
interface HasPosition {
// doesn't matter
}
Attempt to use intersection type:
@SuppressWarnings("unchecked")
<E extends PublicCloneable & HasPosition> E cloneAndIncrementPosition(E elem) {
final E clone = (E)elem.clone();
// rest omitted
}
Attempt to compile with javac 1.8.0_60
:
$ javac xx.java
xx.java:13: error: clone() in Object cannot implement clone() in PublicCloneable
<E extends PublicCloneable & HasPosition> E cloneAndIncrementPosition(E elem) {
^
attempting to assign weaker access privileges; was public
xx.java:14: error: clone() has protected access in Object
final E clone = (E)elem.clone();
^
2 errors
Why this intersection type is invalid for javac?
This looks like a javac bug.
http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.4
The members of a type variable X with bound T & I1 & ... & In are the members of the intersection type (§4.9) T & I1 & ... & In
http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html#jls-4.9
Every intersection type T1 & ... & Tn induces a notional class or interface for the purpose of identifying the members of the intersection type ...
If Ck is Object, a notional interface is induced ... has direct superinterfaces T1', ..., Tn'
Therefore, for PublicCloneable & HasPosition
, a notional interface is introduced, extending both of them, which should be OK.
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