How StackWalker.Option SHOW_HIDDEN_FRAMES works in Java 9

Question

I am studying the StackWalking API introduced in jdk9. I did not see any difference in the output with StackWalker.Option.SHOW_HIDDEN_FRAMESor without an option .

According to the API documentation :

A Java Virtual Machine implementation may hide a specific implementation of frames in addition to reflection frames. StackWalker with this SHOW_HIDDEN_FRAMES option will show all hidden frames (including reflective frames)

Can someone help me figure out which exact frames the JVM can hide in addition to reflection frames? What is the exact use of this option?

This is my demo code:

class DemoClass {

    public static void a() {
        b();
    }

    static void b() {
        c();
    }

    static void c() {
        d();
    }

    static void d() {
        StackWalker sw = StackWalker.getInstance(Set.of(StackWalker.Option.RETAIN_CLASS_REFERENCE, StackWalker.Option.SHOW_HIDDEN_FRAMES));
        sw.forEach(System.out::println);
    }
}

public class StackWalkerAPI {

    public static void main(String[] args) {
        try {
            Method methodA = Class.forName("DemoClass").getMethod("a");
            methodA.invoke(null, (Object[]) null);
        } catch (ClassNotFoundException | NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException ex) {
            Logger.getLogger(StackWalkerAPI.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}

Answer 1

, , Java 9. , , :

StackWalker.Option.RETAIN_CLASS_REFERENCE StackFrames, StackWalker.

internal/experiment.StackWalkerDemo.lambda$d$0(StackWalkerDemo.java:29)
java.base/java.lang.Iterable.forEach(Iterable.java:75)
internal/experiment.StackWalkerDemo.d(StackWalkerDemo.java:28)
internal/experiment.StackWalkerDemo.c(StackWalkerDemo.java:20)
internal/experiment.StackWalkerDemo.b(StackWalkerDemo.java:16)
internal/experiment.StackWalkerDemo.a(StackWalkerDemo.java:12)
internal/experiment.StackWalkerAPI.main(StackWalkerAPI.java:15) 

---

StackWalker.Option.SHOW_REFLECT_FRAMES

internal/experiment.StackWalkerDemo.lambda$d$0(StackWalkerDemo.java:29)
java.base/java.lang.Iterable.forEach(Iterable.java:75)
internal/experiment.StackWalkerDemo.d(StackWalkerDemo.java:28)
internal/experiment.StackWalkerDemo.c(StackWalkerDemo.java:20)
internal/experiment.StackWalkerDemo.b(StackWalkerDemo.java:16)
internal/experiment.StackWalkerDemo.a(StackWalkerDemo.java:12)
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.base/java.lang.reflect.Method.invoke(Method.java:564)
internal/experiment.StackWalkerAPI.main(StackWalkerAPI.java:15)

java.base/java.lang.reflect.Method.invoke(Method.java:564), , , Method.invoke(o1,o2) Constructor.newInstance(o).

---

StackWalker.Option.SHOW_HIDDEN_FRAMES .

internal/experiment.StackWalkerDemo.lambda$d$0(StackWalkerDemo.java:29)
internal/experiment.StackWalkerDemo$$Lambda$23/1358444045.accept(Unknown Source)
java.base/java.lang.Iterable.forEach(Iterable.java:75)
internal/experiment.StackWalkerDemo.d(StackWalkerDemo.java:28)
internal/experiment.StackWalkerDemo.c(StackWalkerDemo.java:20)
internal/experiment.StackWalkerDemo.b(StackWalkerDemo.java:16)
internal/experiment.StackWalkerDemo.a(StackWalkerDemo.java:12)
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.base/java.lang.reflect.Method.invoke(Method.java:564)
internal/experiment.StackWalkerAPI.main(StackWalkerAPI.java:15)

internal/experiment.StackWalkerDemo$$Lambda$23/1358444045.accept(Unknown Source), ( ) .