The `javax.naming.CompoundName`, an extensible type, has a protected member, `impl` whose type, `javax.naming.NameImpl`, is package-private. This is a long standing issue where an inaccessible implementation type has mistakenly made its way into the public Java SE API.
 
The new `javac` lint option `javac -Xlint` helped identify this issue. In Java SE 9, this protected member has been removed from the public API.

Compatibility:
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Since the type of the member is package-private it cannot be directly referenced by non-JDK code. The member type does not implement or extend any super type directly, therefore any non-JDK subtype of `javax.naming.CompoundName` could only refer to this member as Object. It is possible that such a subtype might invoke the `toString`, or any of `Object`'s methods on this member, or even synchronize on it. In such a case such subtypes of `javax.naming.CompoundName` will require updating.
 
Source incompatible:
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Code making a static reference to the member will fail to compile, e.g. `error: impl has private access in CompoundName`

Binary incompatible:
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Previously compiled code executed with JDK 9, accessing the member directly will fail, e.g. `java.lang.IllegalAccessError: tried to access field javax.naming.CompoundName.impl from class CompoundName$MyCompoundName`