Java Inheritance

Question

package com.doubts;
class X{
int a=10;
}
class Y extends X{
int a=20;
}
public class SL1 {
public static void main(String[] args) {
X x = new Y();
System.out.println(x.a);
}
}

// Why output is not 20

Answer 1

class X{
int a=10;
}

class Y extends X{
int a=20;
int super_a() { return super.a; }
}

public class SL1 {
public static void main(String[] args) {
Y y = new Y();
y.a = 200;
// y has a 200
System.out.println( y.a);

// but super a 10 stil exist as hidden
System.out.println( y.super_a() );
System.out.println();

X x = y;
// now y was reduced to his super type
System.out.println( x.a); //10
// and y extensions cannot be accesed
// error:
// System.out.println( x.super_a() );
System.out.println();

Y y2 = (Y) x;
// now y is back and his extensions too
System.out.println( y2.a); //200
System.out.println( y2.super_a() );
}
}

Answer 2

X x = ..
x is of type X and value in X is 10
but you can cast it
System.out.println( ((Y) x).a);

Answer 3

Class X is not abstract, inheritance does not work

Answer 4

I appreciate your attention but still I'm confused can you please elaborate it bit more