以下程序的输出结果为 . class B { int b; B(int x) { b = x; System.out.println("b=" + b); } } class A extends B { int a; A(int x, int y) { super(x); a = y; System.out.println("b=" + b + ",a=" + a); } } public class Test { public static void main(String[] args) { A obj = new A(13, 23); } }