Difference between casting to String and String.valueOf

Question

What is the difference between

Object foo = "something"; String bar = String.valueOf(foo); 

and

Object foo = "something"; String bar = (String) foo; 

Answer 1

Casting to string only works when the object actually is a string:

Object reallyAString = "foo"; String str = (String) reallyAString; // works. 

It won't work when the object is something else:

Object notAString = new Integer(42); String str = (String) notAString; // will throw a ClassCastException 

String.valueOf() however will try to convert whatever you pass into it to a String. It handles both primitives (42) and objects (new Integer(42), using that object's toString()):

String str; str = String.valueOf(new Integer(42)); // str will hold "42" str = String.valueOf("foo"); // str will hold "foo" Object nullValue = null; str = String.valueOf(nullValue); // str will hold "null" 

Note especially the last example: passing null to String.valueOf() will return the string "null".

Answer 2

String.valueOf(foo) invokes foo's .toString() method and assigns the result to the the bar. It is null and type safe operation.

Casting will just assign foo to the bar, if the types are matching. Otherwise, the expression will throw a ClassCastException.