Java Recursive Problems

                         
Java Recursive Problems (4 problems):

Problem  I.    We define the Shaw strings as follows:
      1. abb is a Shaw string.
      2. bca is a Shaw string.
      3. If S is a Shaw string, so is SaS.
      4. If U and V are Shaw strings, so is UbV.

Here a, b, c are constants and S,U,V are variables. In these rules,
the same letter represents the same string. So, if S = abb,
rule 3 tells us that abbaabb is a Shaw string.
In rule 4, U and V represent Shaw strings, but they may be different.

Write the method

public static boolean isShaw(String in)
that returns true if in is a Shaw string and false otherwise.

Problem II.