COBOL Tutorial

COBOL INTERFACE-ID Clause - Quick Reference

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Overview

The INTERFACE-ID clause is used in object-oriented COBOL to define interfaces that specify contracts for classes. Interfaces define a set of methods and properties that implementing classes must provide, enabling polymorphic behavior and promoting loose coupling between components.

Purpose and Usage

Contract definition - Define method signatures and contracts
Loose coupling - Promote loose coupling between components
Polymorphic behavior - Enable polymorphic programming
Testability - Enable easier testing with mock objects
Multiple inheritance - Achieve multiple inheritance-like behavior

Interface Contract Concept

Interface: [Method1 Signature] [Method2 Signature] [Method3 Signature]

Implementing Class: [Method1 Implementation] [Method2 Implementation] [Method3 Implementation]

Contract: Class must implement ALL interface methods

Interface defines the "what", class provides the "how"

Interfaces define contracts that implementing classes must fulfill.

Syntax

The INTERFACE-ID clause follows specific syntax patterns for defining interfaces in object-oriented COBOL.

Basic Syntax

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* Basic INTERFACE-ID clause syntax
INTERFACE-ID interface-name
    [INHERITS parent-interface-name]
    [FACTORY]
    [OBJECT]
    [ENVIRONMENT DIVISION]
    [DATA DIVISION]
    [PROCEDURE DIVISION]
END INTERFACE interface-name.
 
* Examples
INTERFACE-ID IDATABASE-OPERATIONS
    FACTORY.
 
INTERFACE-ID IPAYMENT-PROCESSOR
    INHERITS IBASE-PROCESSOR
    FACTORY.
 
* Complete example
INTERFACE-ID IDATABASE-INTERFACE
    FACTORY.
 
DATA DIVISION.
 
PROCEDURE DIVISION.
 
METHOD-ID CONNECT.
DATA DIVISION.
LINKAGE SECTION.
01  CONNECTION-STRING   PIC X(100).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONNECTION-STRING
    RETURNING RETURN-CODE.
END METHOD CONNECT.
 
METHOD-ID DISCONNECT.
DATA DIVISION.
PROCEDURE DIVISION.
END METHOD DISCONNECT.
 
METHOD-ID EXECUTE-QUERY.
DATA DIVISION.
LINKAGE SECTION.
01  QUERY-STRING        PIC X(500).
01  RESULT-SET          PIC X(1000).
PROCEDURE DIVISION USING QUERY-STRING
    RETURNING RESULT-SET.
END METHOD EXECUTE-QUERY.
 
END INTERFACE IDATABASE-INTERFACE.

INTERFACE-ID defines the interface name and structure.

Interface Components

Component	Purpose	Example
INTERFACE-ID	Define interface name	INTERFACE-ID IPAYMENT-INTERFACE
METHOD-ID	Define method signatures	METHOD-ID PROCESS-PAYMENT
INHERITS	Inherit from parent interface	INHERITS IBASE-INTERFACE
END INTERFACE	End interface definition	END INTERFACE IPAYMENT-INTERFACE

Interface Inheritance

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* Interface inheritance example
INTERFACE-ID IBASE-OPERATIONS
    FACTORY.
 
PROCEDURE DIVISION.
 
METHOD-ID INITIALIZE.
DATA DIVISION.
LINKAGE SECTION.
01  CONFIG-PARAMS       PIC X(200).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONFIG-PARAMS
    RETURNING RETURN-CODE.
END METHOD INITIALIZE.
 
METHOD-ID CLEANUP.
DATA DIVISION.
PROCEDURE DIVISION.
END METHOD CLEANUP.
 
END INTERFACE IBASE-OPERATIONS.
 
INTERFACE-ID IDATABASE-OPERATIONS
    INHERITS IBASE-OPERATIONS
    FACTORY.
 
PROCEDURE DIVISION.
 
METHOD-ID CONNECT.
DATA DIVISION.
LINKAGE SECTION.
01  CONNECTION-STRING   PIC X(100).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONNECTION-STRING
    RETURNING RETURN-CODE.
END METHOD CONNECT.
 
METHOD-ID DISCONNECT.
DATA DIVISION.
PROCEDURE DIVISION.
END METHOD DISCONNECT.
 
METHOD-ID EXECUTE-QUERY.
DATA DIVISION.
LINKAGE SECTION.
01  QUERY-STRING        PIC X(500).
01  RESULT-SET          PIC X(1000).
PROCEDURE DIVISION USING QUERY-STRING
    RETURNING RESULT-SET.
END METHOD EXECUTE-QUERY.
 
END INTERFACE IDATABASE-OPERATIONS.

Interfaces can inherit from other interfaces to create hierarchies.

Common Use Cases

INTERFACE-ID is commonly used in specific scenarios where interface-based programming and contract definition are needed.

Service Layer Contracts

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* Service layer interface definition
INTERFACE-ID IDATABASE-SERVICE
    FACTORY.
 
PROCEDURE DIVISION.
 
METHOD-ID CONNECT.
DATA DIVISION.
LINKAGE SECTION.
01  CONNECTION-STRING   PIC X(100).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONNECTION-STRING
    RETURNING RETURN-CODE.
END METHOD CONNECT.
 
METHOD-ID DISCONNECT.
DATA DIVISION.
PROCEDURE DIVISION.
END METHOD DISCONNECT.
 
METHOD-ID EXECUTE-QUERY.
DATA DIVISION.
LINKAGE SECTION.
01  QUERY-STRING        PIC X(500).
01  RESULT-SET          PIC X(1000).
PROCEDURE DIVISION USING QUERY-STRING
    RETURNING RESULT-SET.
END METHOD EXECUTE-QUERY.
 
METHOD-ID EXECUTE-UPDATE.
DATA DIVISION.
LINKAGE SECTION.
01  UPDATE-STRING       PIC X(500).
01  ROWS-AFFECTED       PIC 9(5).
PROCEDURE DIVISION USING UPDATE-STRING
    RETURNING ROWS-AFFECTED.
END METHOD EXECUTE-UPDATE.
 
END INTERFACE IDATABASE-SERVICE.
 
CLASS-ID ORACLE-DATABASE-SERVICE
    IMPLEMENTS IDATABASE-SERVICE
    FACTORY.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  ORACLE-CONNECTION   PIC X(100).
01  IS-CONNECTED        PIC X VALUE 'N'.
 
OBJECT SECTION.
 
PROCEDURE DIVISION.
 
METHOD-ID CONNECT.
DATA DIVISION.
LINKAGE SECTION.
01  CONNECTION-STRING   PIC X(100).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONNECTION-STRING
    RETURNING RETURN-CODE.
    MOVE CONNECTION-STRING TO ORACLE-CONNECTION
    PERFORM ORACLE-CONNECT
    IF CONNECTION-SUCCESSFUL
        MOVE 'Y' TO IS-CONNECTED
        MOVE 0 TO RETURN-CODE
    ELSE
        MOVE 1 TO RETURN-CODE
    END-IF
    EXIT METHOD.
END METHOD CONNECT.
 
METHOD-ID DISCONNECT.
DATA DIVISION.
PROCEDURE DIVISION.
    IF IS-CONNECTED = 'Y'
        PERFORM ORACLE-DISCONNECT
        MOVE 'N' TO IS-CONNECTED
    END-IF
    EXIT METHOD.
END METHOD DISCONNECT.
 
METHOD-ID EXECUTE-QUERY.
DATA DIVISION.
LINKAGE SECTION.
01  QUERY-STRING        PIC X(500).
01  RESULT-SET          PIC X(1000).
PROCEDURE DIVISION USING QUERY-STRING
    RETURNING RESULT-SET.
    IF IS-CONNECTED = 'Y'
        PERFORM ORACLE-EXECUTE-QUERY
    ELSE
        MOVE 'NOT CONNECTED' TO RESULT-SET
    END-IF
    EXIT METHOD.
END METHOD EXECUTE-QUERY.
 
METHOD-ID EXECUTE-UPDATE.
DATA DIVISION.
LINKAGE SECTION.
01  UPDATE-STRING       PIC X(500).
01  ROWS-AFFECTED       PIC 9(5).
PROCEDURE DIVISION USING UPDATE-STRING
    RETURNING ROWS-AFFECTED.
    IF IS-CONNECTED = 'Y'
        PERFORM ORACLE-EXECUTE-UPDATE
    ELSE
        MOVE 0 TO ROWS-AFFECTED
    END-IF
    EXIT METHOD.
END METHOD EXECUTE-UPDATE.
 
END CLASS ORACLE-DATABASE-SERVICE.

Service layer interfaces define contracts for different implementations.

Plugin Architecture

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* Plugin architecture interface definition
INTERFACE-ID IPLUGIN-INTERFACE
    FACTORY.
 
PROCEDURE DIVISION.
 
METHOD-ID INITIALIZE.
DATA DIVISION.
LINKAGE SECTION.
01  CONFIG-PARAMS       PIC X(200).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONFIG-PARAMS
    RETURNING RETURN-CODE.
END METHOD INITIALIZE.
 
METHOD-ID EXECUTE.
DATA DIVISION.
LINKAGE SECTION.
01  INPUT-DATA          PIC X(500).
01  OUTPUT-DATA         PIC X(500).
PROCEDURE DIVISION USING INPUT-DATA
    RETURNING OUTPUT-DATA.
END METHOD EXECUTE.
 
METHOD-ID CLEANUP.
DATA DIVISION.
PROCEDURE DIVISION.
END METHOD CLEANUP.
 
END INTERFACE IPLUGIN-INTERFACE.
 
CLASS-ID EMAIL-PLUGIN
    IMPLEMENTS IPLUGIN-INTERFACE
    FACTORY.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  SMTP-SERVER         PIC X(50).
01  SMTP-PORT           PIC 9(4).
01  IS-INITIALIZED      PIC X VALUE 'N'.
 
OBJECT SECTION.
 
PROCEDURE DIVISION.
 
METHOD-ID INITIALIZE.
DATA DIVISION.
LINKAGE SECTION.
01  CONFIG-PARAMS       PIC X(200).
01  RETURN-CODE         PIC 9(4).
PROCEDURE DIVISION USING CONFIG-PARAMS
    RETURNING RETURN-CODE.
    PERFORM PARSE-SMTP-CONFIG
    IF CONFIG-VALID
        MOVE 'Y' TO IS-INITIALIZED
        MOVE 0 TO RETURN-CODE
    ELSE
        MOVE 1 TO RETURN-CODE
    END-IF
    EXIT METHOD.
END METHOD INITIALIZE.
 
METHOD-ID EXECUTE.
DATA DIVISION.
LINKAGE SECTION.
01  INPUT-DATA          PIC X(500).
01  OUTPUT-DATA         PIC X(500).
PROCEDURE DIVISION USING INPUT-DATA
    RETURNING OUTPUT-DATA.
    IF IS-INITIALIZED = 'Y'
        PERFORM SEND-EMAIL
        MOVE 'EMAIL SENT' TO OUTPUT-DATA
    ELSE
        MOVE 'PLUGIN NOT INITIALIZED' TO OUTPUT-DATA
    END-IF
    EXIT METHOD.
END METHOD EXECUTE.
 
METHOD-ID CLEANUP.
DATA DIVISION.
PROCEDURE DIVISION.
    MOVE 'N' TO IS-INITIALIZED
    EXIT METHOD.
END METHOD CLEANUP.
 
END CLASS EMAIL-PLUGIN.

Plugin architectures use interfaces for extensible functionality.

Payment Processing Interface

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* Payment processing interface hierarchy
INTERFACE-ID IPAYMENT-INTERFACE
    FACTORY.
 
PROCEDURE DIVISION.
 
METHOD-ID PROCESS-PAYMENT.
DATA DIVISION.
LINKAGE SECTION.
01  AMOUNT             PIC 9(8)V99.
01  RETURN-CODE        PIC 9(4).
PROCEDURE DIVISION USING AMOUNT
    RETURNING RETURN-CODE.
END METHOD PROCESS-PAYMENT.
 
METHOD-ID VALIDATE-PAYMENT.
DATA DIVISION.
LINKAGE SECTION.
01  PAYMENT-DATA       PIC X(200).
01  IS-VALID           PIC X.
PROCEDURE DIVISION USING PAYMENT-DATA
    RETURNING IS-VALID.
END METHOD VALIDATE-PAYMENT.
 
END INTERFACE IPAYMENT-INTERFACE.
 
INTERFACE-ID ICARD-PAYMENT-INTERFACE
    INHERITS IPAYMENT-INTERFACE
    FACTORY.
 
PROCEDURE DIVISION.
 
METHOD-ID AUTHORIZE-CARD.
DATA DIVISION.
LINKAGE SECTION.
01  CARD-NUMBER        PIC X(16).
01  EXPIRY-DATE        PIC X(5).
01  CVV                PIC X(3).
01  AUTHORIZATION-CODE PIC X(10).
PROCEDURE DIVISION USING CARD-NUMBER, EXPIRY-DATE, CVV
    RETURNING AUTHORIZATION-CODE.
END METHOD AUTHORIZE-CARD.
 
END INTERFACE ICARD-PAYMENT-INTERFACE.
 
CLASS-ID CREDIT-CARD-PROCESSOR
    IMPLEMENTS ICARD-PAYMENT-INTERFACE
    FACTORY.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  PROCESSOR-STATUS   PIC X(10).
 
OBJECT SECTION.
 
PROCEDURE DIVISION.
 
METHOD-ID PROCESS-PAYMENT.
DATA DIVISION.
LINKAGE SECTION.
01  AMOUNT             PIC 9(8)V99.
01  RETURN-CODE        PIC 9(4).
PROCEDURE DIVISION USING AMOUNT
    RETURNING RETURN-CODE.
    PERFORM CREDIT-CARD-PROCESSING
    IF PROCESSING-SUCCESSFUL
        MOVE 0 TO RETURN-CODE
    ELSE
        MOVE 1 TO RETURN-CODE
    END-IF
    EXIT METHOD.
END METHOD PROCESS-PAYMENT.
 
METHOD-ID VALIDATE-PAYMENT.
DATA DIVISION.
LINKAGE SECTION.
01  PAYMENT-DATA       PIC X(200).
01  IS-VALID           PIC X.
PROCEDURE DIVISION USING PAYMENT-DATA
    RETURNING IS-VALID.
    PERFORM VALIDATE-CREDIT-CARD
    EXIT METHOD.
END METHOD VALIDATE-PAYMENT.
 
METHOD-ID AUTHORIZE-CARD.
DATA DIVISION.
LINKAGE SECTION.
01  CARD-NUMBER        PIC X(16).
01  EXPIRY-DATE        PIC X(5).
01  CVV                PIC X(3).
01  AUTHORIZATION-CODE PIC X(10).
PROCEDURE DIVISION USING CARD-NUMBER, EXPIRY-DATE, CVV
    RETURNING AUTHORIZATION-CODE.
    PERFORM AUTHORIZE-CREDIT-CARD
    EXIT METHOD.
END METHOD AUTHORIZE-CARD.
 
END CLASS CREDIT-CARD-PROCESSOR.

Interface hierarchies enable specialized payment processing.

Best Practices and Tips

Following these best practices ensures effective use of the INTERFACE-ID clause for interface-based programming.

INTERFACE-ID Design Principles

Single responsibility - Keep interfaces focused on one purpose
Clear naming - Use descriptive interface names
Minimal methods - Define only essential methods
Consistent signatures - Use consistent parameter patterns
Documentation - Document interface contracts clearly
Interface segregation - Avoid large, monolithic interfaces

Common Pitfalls to Avoid

Pitfall	Problem	Solution
Large interfaces	Difficult to implement	Keep interfaces small and focused
Vague contracts	Unclear requirements	Define clear method signatures
Interface bloat	Too many methods	Use interface segregation
Poor naming	Confusing interface names	Use descriptive names
No documentation	Unclear contracts	Document all interfaces

Performance Considerations

Interface call overhead - Interface method calls may have slight overhead
Method resolution - Virtual method table lookups
Interface inheritance - Multiple inheritance can add complexity
Memory footprint - Consider interface implementation memory usage
Optimization opportunities - Some compilers optimize interface calls
Interface granularity - Balance flexibility with performance

When to Use INTERFACE-ID

Use Case	INTERFACE-ID Suitability	Reasoning
Service contracts	Excellent	Perfect for defining service APIs
Plugin architectures	Excellent	Ideal for extensible systems
Polymorphic behavior	Good	Enables polymorphic programming
Simple inheritance	Poor	Use INHERITS instead
Performance-critical code	Poor	Interface overhead may be too high

INTERFACE-ID Clause Quick Reference

Usage	Syntax	Example
Basic interface	INTERFACE-ID interface-name	INTERFACE-ID IPAYMENT-INTERFACE
Interface inheritance	INTERFACE-ID interface-name INHERITS parent	INTERFACE-ID ICHILD INHERITS IPARENT
Method definition	METHOD-ID method-name	METHOD-ID PROCESS-PAYMENT
Interface implementation	IMPLEMENTS interface-name	IMPLEMENTS IPAYMENT-INTERFACE
End interface	END INTERFACE interface-name	END INTERFACE IPAYMENT-INTERFACE

Test Your Knowledge

1. What is the primary purpose of the INTERFACE-ID clause in COBOL?

To define class inheritance
To define interfaces that specify contracts for classes
To create new objects
To define data structures

2. What is the relationship between interfaces and classes?

Interfaces inherit from classes
Classes implement interfaces
Interfaces and classes are the same thing
Interfaces cannot be used with classes

3. Can interfaces inherit from other interfaces?

No, interfaces cannot inherit
Yes, using the INHERITS clause
Only from classes
Only from abstract classes

4. Which of the following is a benefit of using interfaces?

Reduced memory usage
Loose coupling and polymorphic behavior
Faster execution speed
Simpler syntax

5. What happens if a class implements an interface but doesn't provide all required methods?

The program will run normally
A compilation error will occur
The missing methods will be automatically generated
The interface will be ignored

COBOL Tutorial

COBOL INTERFACE-ID Clause - Quick Reference

Overview

Purpose and Usage

Interface Contract Concept

Syntax

Basic Syntax

Interface Components

Interface Inheritance

Common Use Cases

Service Layer Contracts

Plugin Architecture

Payment Processing Interface

Best Practices and Tips

INTERFACE-ID Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use INTERFACE-ID

INTERFACE-ID Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

Related Concepts

IMPLEMENTS Clause

INHERITS Clause

CLASS-ID Clause

METHOD-ID Clause

Object-Oriented Programming

Related Pages

COBOL Tutorial

COBOL INTERFACE-ID Clause - Quick Reference

Overview

Purpose and Usage

Interface Contract Concept

Syntax

Basic Syntax

Interface Components

Interface Inheritance

Common Use Cases

Service Layer Contracts

Plugin Architecture

Payment Processing Interface

Best Practices and Tips

INTERFACE-ID Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use INTERFACE-ID

INTERFACE-ID Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

What is the difference between an interface and a class?

Can interfaces contain data members?

Can interfaces inherit from classes?

Is INTERFACE-ID supported in all COBOL dialects?

How do you test code that uses interfaces?

Related Concepts

IMPLEMENTS Clause

INHERITS Clause

CLASS-ID Clause

METHOD-ID Clause

Object-Oriented Programming

Related Pages