How to cast to a specified class type? [duplicate]-Collection of common programming errors

The cast as you write it does nothing.

The cast serves for assigning an object of a superclass to a subclass reference

Object obj = a.toString();
String str = (String) obj;  // The compiler can't check that at runtime obj will be
                            // a String, so the programmer "forces" the compiler to
                            // allow the assignation

needs a cast, but in

Object obj2 = (String) obj;

the cast does nothing (other than throwing a ClassCastException if obj is not a String).