Operand peek(Register s){
  Stack<Operand> stack=get(s);
  if (stack == null || stack.isEmpty()) {
    return null;
  }
 else {
    return stack.peek();
  }
}

Operand peek ( Register s ) { Stack < Operand > stack = get ( s ) ; if ( stack == null || stack . isEmpty ( ) ) { return null ; } else { return stack . peek ( ) ; } }
get the name at the top of the stack for a particular register
