Complete Program

Here is the complete, revised program. You may wish to play with it. Perhaps add several more objects.

You could add any number of additional objects, but only one copy is needed of each method.

          .globl   main
          .text
main:                                 # object1.print(); 
          la       $a0,object1        #   get address of first object
          lw       $t0,0($a0)         #   get address of print method
          jalr     $t0                #   call the method
                                      # object1.cancel();
          la       $a0,object1        #   get address of first object
          lw       $t0,4($a0)         #   get address of cancel method
          jalr     $t0                #   call the method
                                      # object1.print();
          la       $a0,object1        #   get address of first object
          lw       $t0,0($a0)         #   get address of print method
          jalr     $t0                #   call the method
                                      # object2.print();         
          la       $a0,object2        #   get address of second object
          lw       $t0,0($a0)         #   get address of object's method
          jalr     $t0                #   call the object's method
          
          li      $v0,10              # return to OS
          syscall

# Objects constructed in static memory.
# The implementation of an object consists of the data for each object
# and a jump table of entry points common to all objects
# of this type.

          .data
object1:
          .word    print                    # Jump Table
          .word    cancel
          .asciiz  "Hello World\n"          # This object's data

object2:
          .word    print                    # Jump Table
          .word    cancel
          .asciiz  "Silly Example\n"        # This object's data

# print() method
# Used by all objects.
#
# Parameter: $a0 == address of the object
          .text         
print:
          li       $v0,4                   # print string service
          addiu    $a0,$a0,8               # address of object's string
          syscall                          # 
          jr       $ra
          
# cancel() method
# Used by all objects.
#
# Parameter: $a0 == address of the object
# 
# Registers:
# $t0 == address of the char in the string
# $t1 == char from the string
# $t2 == 'x'

          .text         
cancel:
          addiu    $t0,$a0,8       # the string starts 8 bytes
                                   # from the start of the object
          li       $t2,'x'         # replacement character                             
          lb       $t1,0($t0)      # get first ch of string
loop:     beqz     $t1,done        # while ( ch != '\0' )
          sb       $t2,0($t0)      #   replace ch with 'x'
          addiu    $t0,$t0,1       #
          lb       $t1,0($t0)      #   get next ch
          b        loop            # end while     
done:
          jr       $ra             # return to caller