Question

Possible Duplicate:
String object creation using new and its comparison with intern method

I was playing around with Strings to understand them more and I noticed something that I can’t explain :

String str1 = "whatever";
String str2 = str1;
String str3 = "whatever";
System.out.println(str1==str2); //prints true...that's normal, they point to the same object
System.out.println(str1==str3); //gives true..how's that possible ?

How is the last line giving true ? this means that both str1 and str3 have the same address in memory.

Is this a compiler optimization that was smart enough to detect that both string literals are the same (“whatever”) and thus assigned str1 and str3 to the same object ? Or am I missing something in the underlying mechanics of strings ?

Answer 1

http://www.xyzws.com/Javafaq/what-is-string-literal-pool/3

As the post says:

String allocation, like all object allocation, proves costly in both time and memory. The JVM performs some trickery while instantiating string literals to increase performance and decrease memory overhead. To cut down the number of String objects created in the JVM, the String class keeps a pool of strings. Each time your code create a string literal, the JVM checks the string literal pool first. If the string already exists in the pool, a reference to the pooled instance returns. If the string does not exist in the pool, a new String object instantiates, then is placed in the pool.