Mapping COBOL level 88 to Java

Once in a while comes the issue of mapping COBOL data items with associated level 88 condition values to Java. Since this is a complex question, I thought it deserves an entry of its own.

This is an example of simple COBOL level 88 data item descriptions.

     01  MY-ITEM PIC S9(4) COMP.
         88 WRONG-DATA VALUE -1.
         88 NULL-DATA VALUE 0.

First notice that the 88 levels are associated with an actual data item (MY-ITEM). Level 88 items do not occupy any space in memory themselves.

The way they are used is that somewhere in the code, you can state:

         IF WRONG-DATA THEN ...

The condition will be true if, and only if, MY-ITEM contains -1.

Such code is more readable than the equivalent:

         IF MY-ITEM = -1 THEN ...

So this is what it's all about, an improvement to the readability of your COBOL code.

So how can such a thing map to Java?

First of all, it is easy to confuse COBOL Level 88 with java enums . After all, enums are also a readibility improvement feature and they can be used to replace a value with a meaningful label.

It is tempting to map MY-ITEM with:

    enum MyItem {
        WRONG_DATA(-1), NULL_DATA(0);
        private MyItem(int value) {
            _value = value;
        }

        private int _value;

        final int getValue() {
            return _value;
        }
    };

But there is a fundamental issue in doing so: Enums are actually restrictions. This means only the values that are enumerated (-1 and 0 in our case) are possible.

In the case of COBOL level 88, there are no restrictions on actual values. This means MY-ITEM can contain value 2, which is not described by any level 88.

Furthermore, level 88 are not necessarily atomic values. They can be ranges:

       01  ANOTHER-ITEM PIC S9(4) COMP.
           88 CUST-DATA VALUE 9 THRU 975.

Or even list of values:

       01  YET-ANOTHER-ITEM PIC S9(4) COMP.
           88 VALID-DATA VALUE 2, 7, 15, 245.

By now it should be clear why COBOL level 88 does not automatically map to a java variable of some sort with LegStar.

The legstar-cob2xsd module actually offers an option to map level 88 to XML Schema restrictions in the unlikely case where you are sure the COBOL variable never contains any value outside the enumerated values and enumerated values are atomic. But past that, there is no real support for level 88.