How many Java string objects will be created in the following statement?
String s = "abc" + "xyz";
I guess three?
-
In addition to the answer, also see: stackoverflow.com/questions/1842024/…beny23– beny232011-08-14 23:06:23 +00:00Commented Aug 14, 2011 at 23:06
-
4@Deep - please accept my answer - ie click the hollow tick symbol next to the answer (that is, if you think it's correct - many others seem to)Bohemian– Bohemian ♦2011-08-15 01:35:50 +00:00Commented Aug 15, 2011 at 1:35
Add a comment
|
3 Answers
The compiler creates 1 String per JVM start, because the compiler can determine the resulting String at compile time, it is interned and statically stored in the JVM's String Table.
FYI, if the statement were concatenating variables (not determinable at runtime), 1 String would be created, but it would create a StringBuilder too. The code would compile to:
new StringBuilder().append(abcVar).append(xyzVar).toString()
5 Comments
Tapas Bose
+1 for such an useful answer. Can you please explain "it creates a StringBuilder" or give any source so that I can read it in details. It seems interesting to me.
Daniel Lundmark
If I decompile the result of the class file produced from the code in the original example, I get: String a = "abcdef"; I guess my compiler took a shortcut.
ewan.chalmers
Be aware that the compiler shortcuts will not apply / be the same if either of the Strings you append is a variable rather than a literal.
Artur Nowak
When two literals are concatenated they are automatically joined by compiler. So here it will be only one object. It's very important optimization when you consider e.g. strings broken into several lines for visibility.
fvu
@Bohemian please check the answer to this question : according to the JLS the string will be folded into 1 constant at compile time, just as Daniel noticed. The key here is that we're dealing with constants, not with variables.
The answer is one global String object per program run, and zero new String objects per statement execution. This is because the Java Language Specification says the expression "abc" + "xyz" is a compile-time constant [0], and that no new String object will be created when the statement is executed [1].
References
[0]: http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#5313
Examples of constant expressions:
"The integer " + Long.MAX_VALUE + " is mighty big."
[1]: http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.18.1
If only one operand expression is of type String, then string conversion is performed on the other operand to produce a string at run time. The result is a reference to a String object (newly created, unless the expression is a compile-time constant expression (§15.28)) that is the concatenation of the
Comments
There are three ways to create strings in java
1) we can create a string just by assigning a group of characters to a string type variable
eg:
String s; //declare String type variable,
s="hello"; //assign a group of characters to it
2)we can create an object to string by allocating memory using new operator.This is just like creating an object to any class.
eg: String s =new String("Hello");
3) We can creating the strings is by converting the character arrays into string.
eg: char arr[] = {'p','r','a','s','h','a','n','t'};
