Java 8 Interface clinit invocation

[dankurka]

Originally reported on Google Code with ID 9156

In Java 7 when you instantiate an instance of type Foo that extends type Bar, the clinit
for Bar is run and then the clinit for Foo is run. If Foo extends interface Baz which
contains some static fields, the clinit for Baz is NOT run when Bar is instantiated.

But this stays mostly the same in Java 8 except when interface Baz contains a default
method. In this situation the clinit for Baz IS run when Bar is instantiated, *even
if the default method is unreferenced*.

Reported by stalcup@google.com on 2015-03-20 22:28:56

[dankurka]

Reported by stalcup@google.com on 2015-03-20 22:29:09

• Labels added: Category-Compiler

[dankurka]

JLS section 12.4.1 (https://docs.oracle.com/javase/specs/jls/se8/html/jls-12.html) describes
initialization semantics.

Difference between Java8 and 7:
  - When a class is initialized in 8 all superinterfaces that declare any default methods
should be initialized (12.4.2. step 7 describes the order in which superinterfaces
are to be initialized)
  - when a static interface method is called the interface is initialized

Java 8 gives the compiler some leeway: " Note that a compiler may generate synthetic
default methods in an interface, that is, default methods that are neither explicitly
nor implicitly declared (§13.1). Such methods will trigger the interface's initialization
despite the source code giving no indication that the interface should be initialized."


So if the compiler synthesizes default method, then those interfaces are initialized
as per previous description.

Reported by rluble@google.com on 2015-03-24 16:50:08

[rluble]

Review pending at: https://gwt-review.googlesource.com/#/c/13951/