Fundamentals - SCJP Sun Certified Programmer for Java Platform SE6 - page 25

String Literals and the String Pool
The new keyword is not required for creating the String object “How are you?” because
it is a string literal. String literals get special treatment by the JVM. Behind the scenes,
the JVM instantiates a String object for “How are you?” and stores it in the string pool .
The greeting reference refers to this String object in the pool. Because String objects
in Java are immutable (which means they cannot be changed), the JVM can optimize the
use of string literals by allowing only one instance of a string in the pool. For example,
the following two String references actually point to the same string in the pool, as
shown in the following diagram:
String s1 = “New York”;
String s2 = “New York”;
The String pool
s1
“New York”
s2
You might think if the two references point to the same object, then changing one object
would inadvertently change the value of the other. But String objects are immutable, so
the following statement only changes s2 :
s2 = “New Jersey”;
The reference s2 now points to “New Jersey” , but s1 still points to “New York” , as shown
in the following diagram:
The String pool
s1
“New York”
“New Jersey”
s2