Interfaces in COBOL

In COBOL, we don’t have interfaces in the same way as modern object-oriented languages. However, we can simulate some aspects of interfaces using data structures and procedures. Here’s an example that demonstrates a similar concept:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. GEOMETRY-EXAMPLE.
       
       ENVIRONMENT DIVISION.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 WS-PI PIC 9V9(5) VALUE 3.14159.
       
       01 WS-RECT.
          05 WS-RECT-WIDTH  PIC 9(5)V99.
          05 WS-RECT-HEIGHT PIC 9(5)V99.
       
       01 WS-CIRCLE.
          05 WS-CIRCLE-RADIUS PIC 9(5)V99.
       
       01 WS-SHAPE-TYPE PIC X(10).
       01 WS-AREA       PIC 9(7)V99.
       01 WS-PERIMETER  PIC 9(7)V99.
       
       PROCEDURE DIVISION.
       MAIN-PROCEDURE.
           MOVE 3 TO WS-RECT-WIDTH.
           MOVE 4 TO WS-RECT-HEIGHT.
           MOVE "RECTANGLE" TO WS-SHAPE-TYPE.
           PERFORM MEASURE-SHAPE.
           
           MOVE 5 TO WS-CIRCLE-RADIUS.
           MOVE "CIRCLE" TO WS-SHAPE-TYPE.
           PERFORM MEASURE-SHAPE.
           
           STOP RUN.
       
       MEASURE-SHAPE.
           IF WS-SHAPE-TYPE = "RECTANGLE"
              PERFORM CALCULATE-RECT-AREA
              PERFORM CALCULATE-RECT-PERIMETER
           ELSE IF WS-SHAPE-TYPE = "CIRCLE"
              PERFORM CALCULATE-CIRCLE-AREA
              PERFORM CALCULATE-CIRCLE-PERIMETER
           END-IF.
           
           DISPLAY WS-SHAPE-TYPE " Area: " WS-AREA.
           DISPLAY WS-SHAPE-TYPE " Perimeter: " WS-PERIMETER.
       
       CALCULATE-RECT-AREA.
           COMPUTE WS-AREA = WS-RECT-WIDTH * WS-RECT-HEIGHT.
       
       CALCULATE-RECT-PERIMETER.
           COMPUTE WS-PERIMETER = 2 * (WS-RECT-WIDTH + WS-RECT-HEIGHT).
       
       CALCULATE-CIRCLE-AREA.
           COMPUTE WS-AREA = WS-PI * WS-CIRCLE-RADIUS * WS-CIRCLE-RADIUS.
       
       CALCULATE-CIRCLE-PERIMETER.
           COMPUTE WS-PERIMETER = 2 * WS-PI * WS-CIRCLE-RADIUS.

In this COBOL program, we define data structures for rectangles and circles. We then use a MEASURE-SHAPE procedure that acts similarly to the measure function in the original example. It checks the shape type and calls the appropriate procedures to calculate area and perimeter.

The MAIN-PROCEDURE demonstrates how to use these “geometry” concepts with both a rectangle and a circle.

To run this program, you would typically compile it and then execute the resulting binary. The exact commands depend on your COBOL compiler, but it might look something like this:

$ cobc -x geometry-example.cob
$ ./geometry-example
RECTANGLE Area: 000012.00
RECTANGLE Perimeter: 000014.00
CIRCLE Area: 000078.53
CIRCLE Perimeter: 000031.41

This example demonstrates how we can implement similar functionality to interfaces in COBOL, even though the language doesn’t have built-in support for this concept. We use data structures to represent different shapes and procedures to implement their “methods”.

Methods in COBOL

Enums in COBOL

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Interfaces in COBOL