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https://issues.apache.org/jira/browse/BEAM-13020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17514239#comment-17514239
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Beam JIRA Bot commented on BEAM-13020:
--------------------------------------
This issue was marked "stale-P2" and has not received a public comment in 14
days. It is now automatically moved to P3. If you are still affected by it, you
can comment and move it back to P2.
> Fragile reference to private synthetic this$ field
> --------------------------------------------------
>
> Key: BEAM-13020
> URL: https://issues.apache.org/jira/browse/BEAM-13020
> Project: Beam
> Issue Type: Bug
> Components: sdk-java-core
> Reporter: Liam Miller-Cushon
> Priority: P3
> Labels: starter
>
> The following code is using reflection to access a field with a name starting
> with `this$`:
> [https://github.com/apache/beam/blob/4fbdcca377fb9d804433f3014a7e7dfcef2e02f9/runners/spark/src/main/java/org/apache/beam/runners/spark/SparkNativePipelineVisitor.java#L186]
> The OpenJDK javac generates private synthetic fields with names starting with
> `this$` as an implementation detail of inner classes. In the future that
> implementation detail may be changing, and the `this$` field will no longer
> be generated for all inner classes. For more information about the proposed
> change, see: [https://bugs.openjdk.java.net/browse/JDK-8271717]
> Please consider alternatives to accessing the private synthetic `this$` field
> to ensure this code continues to work after the change. For example, consider
> passing an explicit copy of the enclosing instance to code that needs access
> to it, or adding an explicit getter to the inner class.
> For example, given:
> {code:java}
> class Outer {
> int x;
> class Inner1 {
> int f() {
> return x;
> }
> }
> class Inner2 {
> void g() {
> System.err.println("hello");
> }
> }
> }
> {code}
> Currently `Inner1` and `Inner2` both have a synthetic field named `this$0`
> that stores a reference to `Outer`.
> In the future the implementation detail might be changing to omit the field
> from classes that don't reference the enclosing instance. So in the example,
> `Inner1` would still have the synthetic field because it accesses the field
> `x` in the enclosing instance `Outer`. However `Inner2` would no longer have
> a synthetic field, because it doesn't access any state from its enclosing
> instance.
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