Can i have a practical example for down casting in java?

[jacob deiter]

why down casting is needed in java. Can i have a practical example for down casting in java?. I please do not want an academic example.

[Campbell Ritchie]

It is something you should avoid; lots of casts means your classes are designed badly. Look at this method, which isn't in the List interface. If you want to use it, you have to do some horrible testing with instanceof to prevent class cast exceptions:-

List<Foo> myList = new XYZList<>();
myList.add(...);
// ...
/* Expand list to accommodate 1000000 elements */
if (myList instanceof ArrayList)
{
   ((ArrayList)myList).ensureCapacity(1000000);
}
else if (myList instanceof Vector)
{
   ((Vector)myList).ensureCapacity(1000000);
}

LinkedList doesn't have such a method because the size of a linked list and its capacity are always the same. I shall leave you to work out how to handle such a method in this List implementation.

[Stephan van Hulst]

The only two things I can think of that I use are casting Object to X in my X.equals(Object) implementation, and casting a Graphics reference to a Graphics2D reference when I'm overriding JComponent.paintComponent(Graphics).