I have reached the stage of including a Beanshell sampler and successfully accessing UDV variables.
Beanshell can put integers and / or strings into response message for a regex extractor to take them out again - I am able to get the time in millisec as a string.
The Question: how to get a string number from a User Variable and convert to integer, say just to increment numerically?
I guess that this could be done using a local int variable or Integer object, but how? 
My upbringing is C and I cannot claim Java knowledge; however most of my Beanshell code works as expected and required, i.e I can do string _or_ integer operations on local variables OK, and vars.get( ) and vars.put ( ) work too.
According to Java docs I have read, a variable of class Integer should be creatable with a string as its argument -
but this won't work - causes an error.
Attempting valueOf ( ) or parseInt ( ) from Java  doc also cause an error.
Trying the methods allegedly allowed by Java on a class String cause errors in Beanshell Sampler execution 
(error   messages are coarse-grained and  unhelpful: 
 HTTP response code 500 and response message: "org.apache.jorphan.util.JMeterException: Error invoking bsh method eval"
//
I found info on StringBuffer in a Java book - this looks tantalising again but I still can't see how to use it without error or a void value
I have included more notes and comments below.
Help please ! 
// sprintf ( "what %d", a ) ; // this causes an error with valid int a ; fair enough it's C code
// print (a ) ; // no error but dunno where the result goes to 
//
// 
//  Integer rc ("234" ) ; // as shown in Javadoc: causes an error
// Integer rc = "999" ; // Fails - unsurprising
//  rc = parseInt ("324" ) ;  // error
Integer rc ; // // Works OK !  rc is an Integer which is happy with an int.   - see later
String argh = "234" ;  // this line works OK 
//  rc = valueOf ( argh ); // error
// rc = argh.valueOf ( ) ;  // error
 rc = 999 ; // can assign value to an Integer
String foo = "Foo" ; // OK
foo = foo + rc.toString ( ) ; // CAN convert Integer to string - foo gets concatenation as expected
//CAN access variables as strings and copy to local String variable - this one is "88" as set earlier in script
String bar = vars.get("Siebel_Count") ; 
// rc = bar ;  // can't just assign integer to string // 
// rc = bar.toInteger ( ) ;// Fails
// rc = Integer (bar ) ;   // Fails
//  StringBuffer SB ; // no error but what use is this? 
StringBuffer SB ( bar ) ; //  no error but SB is void when concatenated into ResponseMessage as below
//  SB =  "bar"  ;  // error
// Some working code - integer arithmetic
int  result ;
int a = 4 ;
    result = (a+3) * 6 ; // CAN do arithmetic on these int variables
    rc = rc + result ; // OK to add int to Integer //
 //  foo = toString (result ) ; // Error
ResponseMessage = "output =  "  + foo  + " " + result  + " " + (rc+3) + "SB = " + SB ;  // OK with integers or strings: concatenates not adds!



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