There is a subtle differences between String object and string literal.
String s = "abc"; // creates one String object and one reference variable
In this simple case, "abc" will go in the pool and s will refer to it.
String s = new String("abc"); // creates two objects,and one reference variable
In this case, because we used the new keyword, Java will create a new String object
in normal (non-pool) memory, and s will refer to it. In addition, the literal "abc" will
be placed in the pool.
