Java Inner Classes (reflection, javap -private) JDK 17

I want to know how inner classes mechanism works (JDK 17). I'm reading a book Java and I'm learning about inner classes.

For example I have this:

package com.example;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.Instant;
public class TalkingClock {
private int interval;
private  boolean beep;
public TalkingClock(int interval, boolean beep) {
this.interval = interval;
this.beep = beep;
}
public void start(int interval, boolean beep) {
class TimePrinter implements ActionListener {
@Override
public void actionPerformed(ActionEvent actionEvent) {
System.out.println("Kiedy uslyszysz dzwiek, bedzie godzina " + Instant.ofEpochMilli(actionEvent.getWhen()));
if(TalkingClock.this.beep) Toolkit.getDefaultToolkit().beep();
//System.out.println(interval);
}
}
var listener = new TimePrinter();
var timer = new Timer(interval, listener);
timer.start();
}
}

And this info showed after had compiled the code and typed command: javap -private com.example.TalkingClock\$1TimePrinter:

Compiled from "TalkingClock.java"
class com.example.TalkingClock$1TimePrinter implements java.awt.event.ActionListener {
final com.example.TalkingClock this$0;
com.example.TalkingClock$1TimePrinter(com.example.TalkingClock);
public void actionPerformed(java.awt.event.ActionEvent);
}

Okay I can see extra param com.example.TalkingClock in the constructor.
but when I will uncomment //System.out.println(interval); in start() method, I can see:

Compiled from "TalkingClock.java"
class com.example.TalkingClock$1TimePrinter implements java.awt.event.ActionListener {
final int val$interval;
final com.example.TalkingClock this$0;
com.example.TalkingClock$1TimePrinter();
public void actionPerformed(java.awt.event.ActionEvent);
}

Okay extra val$interval is properly added but where is extra param com.example.TalkingClock in the constructor for TalkingClock.this.beep?

On the other hand I have written a reflection code.

In the first case it shows:

class com.example.TalkingClock$1TimePrinter implements java.awt.event.ActionListener{
com.example.TalkingClock$1TimePrinter(com.example.TalkingClock);
public void actionPerformed(java.awt.event.ActionEvent);
final com.example.TalkingClock this$0;
}

in the other:

class com.example.TalkingClock$1TimePrinter implements java.awt.event.ActionListener{
com.example.TalkingClock$1TimePrinter(com.example.TalkingClock, int);
public void actionPerformed(java.awt.event.ActionEvent);
final int val$interval;
final com.example.TalkingClock this$0;
}

And this info is logically for me. But why the tool javap shows me something else?

Thank you for help!!

//edit

The reflection code:

public static void main(String[] args) throws ClassNotFoundException {
String name = "com.example.TalkingClock$1TimePrinter";
Class cl = Class.forName(name);
String modifiers = Modifier.toString(cl.getModifiers());
if(modifiers.length() > 0) System.out.print(modifiers + " ");
if(cl.isSealed()) System.out.print("sealed " + name);
if(cl.isEnum()) System.out.println("enum " + name);
if(cl.isRecord()) System.out.println("record " + name);
if(cl.isInterface()) System.out.println("interface " + name);
else System.out.print("class " + name);
Class supercl = cl.getSuperclass();
if(supercl != null && supercl != Object.class) System.out.print(" extends " + supercl.getName());
printInterfaces(cl);
printPermittedSubclasses(cl);
System.out.println("{\n");
printConstructors(cl);
System.out.println();
printMethods(cl);
System.out.println();
printFields(cl);
System.out.println("}\n");
}
public static void printInterfaces(Class cl) {
Class<?>[] interfaces = cl.getInterfaces();
for (int i = 0; i < interfaces.length; i++) {
if (i == 0) {
System.out.print(cl.isInterface() ? " extends " : " implements ");
} else
System.out.print(", ");
System.out.print(interfaces[i].getName());
}
}
public static void printConstructors(Class cl) {
Constructor[] constructors = cl.getDeclaredConstructors();
for (Constructor c : constructors) {
String name = c.getName();
System.out.print("  ");
String modifiers = Modifier.toString(c.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.print(name + "(");
Class[] paramTypes = c.getParameterTypes();
for (int j = 0; j < paramTypes.length; j++) {
if (j > 0) System.out.print(", ");
System.out.print(paramTypes[j].getName());
}
System.out.println(");");
}
}
public static void printMethods(Class cl) {
Method[] methods = cl.getDeclaredMethods();
for (Method m : methods) {
Class retType = m.getReturnType();
String name = m.getName();
System.out.print("  ");
String modifiers = Modifier.toString(m.getModifiers());
if (modifiers.length() > 0)
System.out.print(modifiers + " ");
System.out.print(retType.getName() + " " + name + "(");
Class[] paramTypes = m.getParameterTypes();
for (int j = 0; j < paramTypes.length; j++) {
if (j > 0)
System.out.print(", ");
System.out.print(paramTypes[j].getName());
}
System.out.println(");");
}
}
public static void printFields(Class cl) {
Field[] fields = cl.getDeclaredFields();
for (Field f : fields) {
Class type = f.getType();
String name = f.getName();
System.out.print("  ");
String modifiers = Modifier.toString(f.getModifiers());
if (modifiers.length() > 0) System.out.print(modifiers + " ");
System.out.println(type.getName() + " " + name + ";");
}
}
public static void printPermittedSubclasses(Class cl) {
if (cl.isSealed()) {
Class<?>[] permittedSubclasses = cl.getPermittedSubclasses();
for (int i = 0; i < permittedSubclasses.length; i++) {
if (i == 0)
System.out.print(" permits ");
else
System.out.print(", ");
System.out.print(permittedSubclasses[i].getName());
}
}
}

> Okay extra val$interval is properly added but where is extra param com.example.TalkingClock in the constructor for TalkingClock.this.beep?

It isn't there because that wouldn't make any sense. Imagine you wrote TalkingClock.this.beep.toLowerCase() (and beep was a string) - would you expect a field for that too?

The thing you are referring to that needs to be available to the inner class is just TalkingClock.this, that is all - once you have that, the code can simply invoke the field lookup for beep on this. Yes, it's private, but that's why the compiler actually made it package private (or, if you're doing this on JDK17, why there's a nestmates section). Access control and making sure all the things the inner class needs are available to it are mostly separate concerns. javac needs to do some fancy footwork to accomodate the fact that at the class file level inner class do not exist - for both of those concepts.

this$0 is TalkingClock.this. Thus, TalkingClock.this.beep in java code turns, at the class file level, into:

load up the this$0 variable. Then fetch the beep field from the object that variable is pointing at.

> On the other hand I have written a reflection code.

You didn't paste this code so there's not much to say here.