Upcasting& downcasting

Question

https://code.sololearn.com/cRr3Tw4k2riq/?ref=app

Could anyone clear my doubt..

Answer 1

//what methods and variables does superclass and subclass access in upcasting
Upcasting is implicit,automatic , which is dame as inheritance, but difference is using parent class refference varisble. It does not change original object.
So all variables,methods access are same as inheriting and accessing in subclass.
//what methods and methods does superclass and subclass access downcasting access
if it successfully,then all methods of subclass, super class methods which are not overridden..

//what is purpose of these upcasting downcasting?
Usefull for making object to target type of object from more general type of object to specific type of object. Grnerics are best examples..

class superclass
{
}

class childclass1 extends superclass
{
}
class childclass2 extends superclass
{
}
class demo
{
public static void main(String[] args){
superclass s= new superclass();//normal

childclass c = new childclass();//normal

superclass upc = new childclass();//upcasting
System.out.println(upc.a);
//this can be cal

Answer 2

Ctd:
superclass upc = new childclass();//upcasting
System.out.println(upc.a);
//this can be called through 's' why upcasting?
Yes. But in that case you cannot call subclass objects by s object.
But by after cast you can do that now, with one object only.; otherwise you have 2 object in object pool with redundant code references.

childclass dc = (childclass)upc;//downcasting
System.out.println(dc.sing());/*this can be called through line 46,means through'c' so y downcasting*/
Yes. But you declared child class object when you have already a refference variable, which you can use..

See i modfied code that if you have another subclass childclass2, then you can refference through c object for childclass2 methods, you need casting like childclass2 dc2=(childclass2)upc;
Like this we can have many classes.. Not only single one.
}

It is in my opinion, there i may missing some points...
Lets discuss with others, if I miss or wrong anything...
https://javarevisited.blogspot.com/2012/12/what-is-type-casting-in-java-c

Answer 3

tqsm Jayakrishna🇮🇳

Answer 4

Haritha Vuppula You're welcome..

Edit:
For clear info, read this link below, about example ArrayList..
ArrayList l = new ArrayList();
In to this list, you can add any type data..
But if you only integers, then you need down casting to
ArrayList<Integer> l = new ArrayList() ;

https://javarevisited.blogspot.com/2012/12/what-is-type-casting-in-java-class-interface-example.html?m=1

Also may this helps..
https://medium.com/@shivachetan0/upcasting-and-downcasting-in-java-f454f173e1ef