java:explain the solution in details

Consider the class Foo and its subclass Bar: public class Foo ( protected int y-0; public Foo(int y) l this . y = y ; public int getY) l return y; public void add(int n) i for (int i = 0 ; i n ; i++) inc ) public void inc) l Y+ti public class Bar extends Foo( private int z = 0; public Bar (int y) l super (y); this. z = 2*y