COMMON statement

COMMON statements are widely used in FORTRAN libraries as a means to implement global data, and allow storage sharing among different program units. In Java, public static variables can be accessed and shared from all other classes. So we convert a COMMON block into a class with variables in the COMMON block being translated into public static variables in the class.

In this case, some additional naming rules are needed:

• Blank common block is converted into class named NonameCommon;
• Named common block retains its name as the class name;
• The members of the class derived from common block inherit the original variable names from the first occurrence of the common block declaration.

As an example, the following FORTRAN program,

   program comm
   integer a,b,fff,i1,i2
   real d,f,f10
   common a,b,d
   common /c0/fff,f
   a =0
   b =10
   d = 5.0 
   fff = 987.0
   f = 3.456
   end

   integer function myfunc()
   integer b,d,i
   real c,f1,f2
   common b,d,c
   common /c0/i,f1
   b = 10
   d = 5
   c = 0.1
   i = 3
   f1 =19.844
   myfunc = d + b
   end

is translated into

   class NonameCommon {
      public static int a;
      public static int b;
      public static float  d;
   }

   class c0_c {
      public static int fff;
      public static float  f;
   }

   class comm_mc {
      public static void main(String args[]) {
         myfunc_c myfunc_o ;
         int ReplaceMentVar0,i1,i2 ;
         float ReplaceMentVar1,f10 ;
        
         NonameCommon.a = 0 ;
         NonameCommon.b = 10 ;
         NonameCommon.d = (float)5.0 ;
         c0_c.fff = (float)987.0 ;
         c0_c.f = (float)3.456 ;
      }
   } 

   class myfunc_c {
      public static int myfunc() {
         int  ReplaceMentVar2 ;
         float  ReplaceMentVar3,f2 ;
        
         NonameCommon.a = 10 ;
         NonameCommon.b = 5 ;
         NonameCommon.d = (float)0.1 ;
         c0_c.fff = 3 ;
         c0_c.f = (float)19.844 ;
         return(NonameCommon.b+NonameCommon.a);
      }
   }

This scheme solves global variable problem, and partly solves storage sharing problem. It fails when two corresponding common variables have different type, such as in

   PROGRAM MAIN
   INTEGER A, B, C
   COMMON /C1/A,B,C
   ...
   END

   SUBROUTINE FOO()
   REAL X,Y,Z
   COMMON /C1/X,Y,Z
   ...
   END

A similar drawback is also associated with our current treatment for EQUIVALENCE statement.