This is a follow-up question to some previous questions about String initialization in Java.
After some small tests in Java, I'm facing the following question:
Why can I execute this statement
String concatenated = str2 + " a_literal_string";
when str2
a String
object initialized to null
( String str2 = null;
) but I cannot call the method toString()
on str2
? Then how does Java do the concatenation of a null String object and a string literal ?
By the way, I tried also to concatenate an Integer initialized to null and the string literal "a_literal_string"
and I've got the same thing that is "null a_literal_string"
in the console. So whichever kind of null gives the same thing?
PS : System.out.println(concatenated);
gives null a_literal_string as output in the console.
This line:
String concatenated = str2 + " a_literal_string";
is compiled into something like
String concatenated = new StringBuilder().append(str2)
.append(" a_literal_string")
.toString();
This gives "null a_literal_string"
(and not NullPointerException
) because StringBuilder.append
is implemented using String.valueOf
, and String.valueOf(null)
returns the string "null"
.
I tried also to concatenate an Integer initialized to null and the string literal "a_literal_string" and I've got the same thing
This is for the same reason as above. String.valueOf(anyObject)
where anyObject
is null
will give back "null"
.
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