use jacoco instrument command to get probed class and it seems strange

[Jiajie Zhuang]

this is my source code :

public class App { 

 public static void main(String[] args) throws InterruptedException { 

 System.out.println( "invoke invoke main" ); 

 while( true ) { Thread.currentThread().sleep( 1000 ); 

 System.out.println( new Date() ); 

 }

 }

 }

and this is the class I got by using instrument command 

public class App { 

 public App() { 

 boolean[] var2 = (boolean[])"$jacocoData"; 

 super(); 

 var2[0] = true; 

 } 

 public static void main(String[] args) throws InterruptedException { 

 boolean[] var2 = (boolean[])"$jacocoData"; 

 System.out.println("invoke invoke main"); 

 var2[1] = true; 

 while(true) { 

 Thread.currentThread(); 

 Thread.sleep(1000L); 

 var2[2] = true; 

 System.out.println(new Date()); 

 var2[3] = true; 

 } 

 } 

}

why the static field $jacocoData and init method $jacocoInit() are not in the class file?

this is the stackoverflow link

https://stackoverflow.com/staging-ground/79195734