// IV4: continuing our exploration of how/whan Java sets instance variables.

public class iv4 {
    public static void main(String[] args) {
	
	new B(1,2);

    }
}

class A {
    int x; int y=x;
    A(int a, int b) {
	System.out.println("A (xy1): "+x+" "+y);
	x = a; y = b;
    	System.out.println("A (xy2): "+x+" "+y);
    }
}

class B extends A {
    int a=1; int b=a;
    B(int q, int r) {

	// Want to check $a$ and $b$, but can't until $super$ is called:
	// System.out.println("B (ab): "+a+" "+b);
	// If you remove the comments, you will get 2 errors:
	// 1. No constructor matching A() found in class A
	//    (because Java automatically tries the default constructor
	//     if you don't provide a call to the $super$ constructor)
	// 2. Constructor invocation must be the first thing in a method.
	//    (becase you tried giving $super$ later in the code)
	// You may fix by writing an empty constructor in class $A$ or
	// move the code "later," as show below.

	super(q,r);
	System.out.println("B (xy1): "+x+" "+y);
	x = q; y = r;
    	System.out.println("B (xy2): "+x+" "+y);
	System.out.println("B (ab1): "+a+" "+b);
	a = x; b = y;
	System.out.println("B (ab2): "+a+" "+b);
    }
    
}
/* output:
A (xy1): 0 0
A (xy2): 1 2
B (xy1): 1 2
B (xy2): 1 2
B (ab1): 1 1
B (ab2): 1 2
*/