Why switch on String compiles into two switches

Question

I read JVM specification on compiling switches and became interested in how switch statement on String is compiled. Here is the test method I examined (JDK1.7.0_40):

Answer 1

The cite from the javac source code:

         * The general approach used is to translate a single
         * string switch statement into a series of two chained
         * switch statements: the first a synthesized statement
         * switching on the argument string's hash value and
         * computing a string's position in the list of original
         * case labels, if any, followed by a second switch on the
         * computed integer value.  The second switch has the same
         * code structure as the original string switch statement
         * except that the string case labels are replaced with
         * positional integer constants starting at 0.
         *
         * The first switch statement can be thought of as an
         * inlined map from strings to their position in the case
         * label list.  An alternate implementation would use an
         * actual Map for this purpose, as done for enum switches.
         *
         * With some additional effort, it would be possible to
         * use a single switch statement on the hash code of the
         * argument, but care would need to be taken to preserve
         * the proper control flow in the presence of hash
         * collisions and other complications, such as
         * fallthroughs.  Switch statements with one or two
         * alternatives could also be specially translated into
         * if-then statements to omit the computation of the hash
         * code.