/**
 * Type equivalence in Java.  
 * There is not real notion of two type being the same in Java
 * You can define a class to inherit from another without any 
 * change (as B does from B below) but they are not equivalent
 * 
 * Java allows comparison of instances either view equals or ==
 * BUT, when you get to function calls functions that expect B
 * will NOT accept A.
 * 
 * @author gtowell
 * Created: July 2022
 */
public class Equiv {
    /**
     * A very simple class
     */
    private class A {
        int b; // Not really used, but I felt like it need to be there

        @Override
        public String toString() {
            return String.format("%s %d", this.getClass().getName(), b);
        }

    }

    /**
     * B extends A without change.  
     * This does not create equivalent types
     */
    private class B extends A {

    }

    /**
     * A function that expects something of type A. 
     * B will also be allowed
     * @param aa
     */
    public void accA(A aa) {
    }

    /**
     * A function that expects something of type B
     * A will not be allowed.
     * @param bb
     */
    public void accB(B bb) {
        
    }

    /**
     * A little testing function
     */
    public void test() {
        A a = new A();
        B b = new B();
        System.out.format("%s\n%s\n", a, b);
        System.out.println(a.equals(b));
        System.out.println(a == b);
        accA(a);
        accA(b);
        accB(a); // Does not compile because of this line!! Explain!!
        accB(b);
    }
    public static void main(String[] args) {
        new Equiv().test();
    }
}