Question

I have a generic implementation of a Stack. An object of this Stack has the name stak and is of the type Character.

I tried

if ( ( ((String)(stak.head).equals("{")) && (str.charAt(i)=='}') )  { /* do something */}

The code compiles correctly but it gives me following error on runtime:

Exception in thread "main" java.lang.ClassCastException: java.lang.Character can
not be cast to java.lang.String
        at One.main(One.java:36)

However, the following code works:

if ( ((Character)(stak.head) == '{') && (str.charAt(i)=='}') )  { /* do something */}

Can you please explain why doesn’t the character object get cast into String?

Answer 1

Simply because Character is not a String, doesn’t fall in the common hierarchy and hence doesn’t allow casting. You can try casting a List to an ArrayList because the compiler knows that they share a common inheritance tree. Also, if you have a generic implementation of a Stack, you really shouldn’t be relying on concrete types like this so I wonder what you’ve got in your code.

Also, { getting converted to Character is not about casting but about auto-boxing/unboxing.