Private function should not call

Question

I come across a strange thing in Java while doing Inheritance :
Problem is that when we have one super class with a public function in it
and a child class calling that function with its own object then everything
works fine.
But the problem arise when we modify super class function to make it private
and add some more "println()" just to know more clearly what is happening
now compile only super class .java file and try to execute child. u will
find it also work fine but private function should not call.
example (do as follow):
Before Changes
1) SuperClass.java
public class SuperClass
public SuperClass(){} //constructor
public void fun() // public function
System.out.println("Super class function called");
2) javac SuperClass.java
3) ChildClass.java
public class ChildClass extends SuperClass
public ChildClass() {} //constructor
public static void main(String [] args)
ChildClass c1 = new ChildClass();
c1.fun();
4) javac ChildClass.java
5) java ChildClass
Output :
Super class function called
After Change
1) SuperClass.java
public class SuperClass
public SuperClass(){} //constructor
private void fun() //private function ***** CHANGED ***********
System.out.println("Super class function called");
System.out.println("Newly added line is displayed");
2) javac SuperClass.java
3) java Child
output:
Super class function called
Newly added line is displayed
Why this "Newly added line is displayed" is in output ?
Probably you will say Child.java should also compile but we haven't make any
changes in it.
And question is that if we have old binary then we can easily bridge the
data hiding concept.
Please take me out of this problem.

Answer 1

Unlike C++, a subclass does not include all the methods/data of the super class.
Instead it is built from the sub class and all its super classes when loaded.
This means you can change a super class, or any class it refers to and the Child class is impacted by this.
The leason is always re-compile all the class which are effected by a change.
Using ant, maven or an IDE will do this.
You can plenty of stange behaviour by recompiling a parent class with compiling its children or the classes which depend on them.