What is the difference between
Object foo = "something";
String bar = String.valueOf(foo);
and
Object foo = "something";
String bar = (String) foo;
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17Uh, they are not the same ... at all.Perception– Perception2013-05-29 13:32:54 +00:00Commented May 29, 2013 at 13:32
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8 Answers
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".
8 Comments
Joachim Sauer
@AdamStelmaszczyk: I doubt there's any that's relevant. Maybe casting is slightly faster, but the other differences (null handling, ability to handle other types) are just significantly more important than any minor performance difference that there might be.
Kevin
To push this question a little further, is there any significant difference between calling
String.valueOf() and obj.toString()? (The first one that comes to my mind is that obj.toString() will through an exception if obj is null.)Joachim Sauer
@Kevin: for reference types (a.k.a "objects") the only difference is what happens with
null. If you look at the implementation of String.valueOf() in your JDK you'll see that all it does for non-null references is to call toString().
k_rollo
Tried
str = String.valueOf(null) in Java 7 Update 80, it throws a NullPointerException.Joachim Sauer
@silver: Indeed, I oversimplified.
String.valueOf((Object) null) will return the String "null". Calling it with a literal null will call String#valueOf(char[]) which actually throws a NPE when you pass in null. |
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.
1 Comment
Ryan Amos
+1 For explaining that
String.valueOf(Object) invokes Object.toString()Casting means that the object needs to be of type String, while String.valueOf() can take other types as well.
Comments
Both generates same output in case of String.
Casting fails in case of provided object is Not a string.
Comments
String.valueOf method is used to get the String represenation of it's parameter object.
(String) value casts object value to string.
You can use the String.valueOf method to get the String representation of an object without worrying about null references. If you try to cast String on a null reference you would get a NullPointerException.
Comments
final Object obj = null; final String strValOfObj = String.valueOf(obj); final String strCastOfObj = (String) obj; if (strValOfObj == null) System.out.println("strValOfObj is null"); if (strCastOfObj == null) System.out.println("strCastOfObj is null");
Output: strCastOfObj is null
Comments
The first one i.e, String.valueOf returns a string only if the object is a representable type which is a value type or a String.. Else it throws the exception.
In the latter one, you are directly casting which can fail if the object isn't a string.
Online example.
answered May 29, 2013 at 13:33
Sri Harsha Chilakapati
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1 Comment
Yousha Aleayoub
What type of exception?
in String.valueOf(); string as work typecasting all the argument passed in valueof() method convert in String and just like integer.string() convert integer into string only
