Java. Instance variable value access via this operator

Question

i need someone help with this little code snippet; why is the output: b 3 and not b 13 as expected?

public class Foo{ 
    int a = 3;
    public void addFive() { a+=5; System.out.println("f");}  
}

class Bar extends Foo{
int a = 8;
public void addFive() { this.a+=5; System.out.println("b");}  

public static void main(String[] args) {
    Foo f = new Bar();
    f.addFive();
    System.out.println(f.a);// why b 3 and not b 13 ??
    }
}

Answer 1

Foo and Bar have two different a fields; Java does not have any notion of field overriding.

Calling f.addFive() calls the derived version of the method (since Java does do method overriding), which modifies Bar.a.
However, accessing f.a returns Foo.a (since f is declared as Foo), which was never changed.