/**
 * File: ConversionI.java
 * Author: Ying Li
 * Date: 09/29/2019
 */

public class ConversionI {
	
	public static void main (String[] argv) {
        short i = 3;
        int j = 2147483647;
        // Java will do implicit conversion for the operation, but not the assignment
        short s = (short) (i + j);
        System.out.println("short " + i  + " int j " + j + "  short s " + s);
        int n = i + j;
        System.out.println("short " + i  + " int j " + j + "  int n " + n);
        
        int a = 1;
        Integer b = 2;
        int c = a + b; // b is unboxed before being added to a.
        Integer d = a + b; // b is unboxed, then the sum is boxed.
        System.out.println( a );
        System.out.println( b );
        System.out.println( c );
        System.out.println( d );

		Parent p1 = new Parent(100);
		System.out.println("p1 is " + p1);
		System.out.println("p1 is happy " + p1.isHappy());
		
		Child  c1 = new Child(101);
		System.out.println("c1 is " + c1);
		System.out.println("c1 is happy " + c1.isHappy());
		System.out.println( "c1 has age " + c1.age());
		
		Parent p2 = new Child(102);
		System.out.println("p2 is " + p2);
		System.out.println("p2 is happy " + p2.isHappy()); // dynamic dispatching!!! It will call the "right" method - Child... 
// 		System.out.println( "p2 has age " + p2.age()); // can't do this!!!
		
		Child c3 = (Child) p2; // downcast
		System.out.println("c3 is " + c3);
		System.out.println("c3 is happy " + c3.isHappy());
		System.out.println( "c3 has age " + c3.age()); // works now!
		
// 		Child c2 = (Child) p1; // compiles, but causes a runtime error
// 		System.out.println("c2 is " + c2);
// 		System.out.println("c2 is happy " + c2.isHappy());
// 		
        // Casting (explicit conversion) doesn't change the bits of the reference, it just changes
        // what operations appear available to the compiler
		Parent p3 = (Parent) c1; // this cast does not change the methods actually available to the object.
		Child c4 = (Child) p3;  // because we can cast back.
		System.out.println( "c4 has age " + c4.age()); // works now!
// 		
	}	
}

class Parent {
	
	protected long id;
	
	public Parent (long id) { this.id = id; }
	
	public String toString () { return Long.toString(id); }
	
	public boolean isHappy () { return false; }
}

class Child extends Parent {
	
	public Child (Integer id) { super(id); }
	
	public boolean isHappy () { return true; }
	
	public int age() { return 2; }
}