COBOL Tutorial

COBOL IMPLEMENTS Clause - Quick Reference

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Overview

The IMPLEMENTS clause is used in object-oriented COBOL to specify that a class implements one or more interfaces. This clause enables polymorphism and ensures that the class provides all the methods and properties defined in the specified interfaces.

Purpose and Usage

Interface implementation - Provide concrete implementations for interface methods
Contract-based programming - Ensure classes meet interface requirements
Polymorphic behavior - Enable objects to be treated as interface instances
Code flexibility - Allow for pluggable components and services
Testability - Enable easier unit testing with mock objects

Interface Implementation Flow

Interface: [Method1] [Method2] [Method3] [Method4]

Class Implementation: [Method1] [Method2] [Method3] [Method4]

Contract: Class must implement ALL interface methods

IMPLEMENTS ensures contract compliance

Classes implementing interfaces must provide all required method implementations.

Syntax

The IMPLEMENTS clause follows specific syntax patterns for defining interface implementations in object-oriented COBOL.

Basic Syntax

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* Basic IMPLEMENTS clause syntax
CLASS-ID class-name
    IMPLEMENTS interface-name-1, interface-name-2, ...
    [INHERITS parent-class-name]
    [FACTORY]
    [OBJECT]
    [ENVIRONMENT DIVISION]
    [DATA DIVISION]
    [PROCEDURE DIVISION]
END CLASS class-name.
 
* Examples
CLASS-ID DATABASE-CONNECTION
    IMPLEMENTS IDATABASE-INTERFACE
    FACTORY.
 
CLASS-ID FILE-MANAGER
    IMPLEMENTS IFILE-OPERATIONS, ILOGGING, ISERIALIZABLE
    FACTORY.
 
* Complete example
CLASS-ID PAYMENT-PROCESSOR
    IMPLEMENTS IPAYMENT-INTERFACE
    INHERITS BASE-PROCESSOR
    FACTORY.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  PROCESSOR-STATUS    PIC X(10).
01  TRANSACTION-COUNT   PIC 9(5).
 
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 VALIDATE-PAYMENT
    IF PAYMENT-VALID
        PERFORM PROCESS-TRANSACTION
        MOVE 0 TO RETURN-CODE
    ELSE
        MOVE 1 TO RETURN-CODE
    END-IF
    EXIT METHOD.
END METHOD PROCESS-PAYMENT.
 
END CLASS PAYMENT-PROCESSOR.

IMPLEMENTS specifies interfaces that a class must implement.

Interface Definition

Clause	Purpose	Example
INTERFACE-ID	Define interface structure	INTERFACE-ID IPAYMENT-INTERFACE
METHOD-ID	Define interface methods	METHOD-ID PROCESS-PAYMENT
IMPLEMENTS	Specify interface implementation	IMPLEMENTS IPAYMENT-INTERFACE
END INTERFACE	End interface definition	END INTERFACE IPAYMENT-INTERFACE

Multiple Interface Implementation

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* Implementing multiple interfaces
CLASS-ID COMPREHENSIVE-SERVICE
    IMPLEMENTS IDATABASE-INTERFACE, ILOGGING-INTERFACE, ISECURITY-INTERFACE
    FACTORY.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  SERVICE-STATUS      PIC X(10).
01  LOG-LEVEL           PIC X(10).
 
OBJECT SECTION.
 
PROCEDURE DIVISION.
 
* IDATABASE-INTERFACE methods
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.
    PERFORM ESTABLISH-DB-CONNECTION
    EXIT METHOD.
END METHOD CONNECT.
 
* ILOGGING-INTERFACE methods
METHOD-ID LOG-MESSAGE.
DATA DIVISION.
LINKAGE SECTION.
01  MESSAGE             PIC X(200).
01  LEVEL               PIC X(10).
PROCEDURE DIVISION USING MESSAGE, LEVEL.
    PERFORM WRITE-TO-LOG
    EXIT METHOD.
END METHOD LOG-MESSAGE.
 
* ISECURITY-INTERFACE methods
METHOD-ID AUTHENTICATE.
DATA DIVISION.
LINKAGE SECTION.
01  USERNAME            PIC X(20).
01  PASSWORD            PIC X(20).
01  IS-AUTHENTICATED    PIC X.
PROCEDURE DIVISION USING USERNAME, PASSWORD
    RETURNING IS-AUTHENTICATED.
    PERFORM VALIDATE-CREDENTIALS
    EXIT METHOD.
END METHOD AUTHENTICATE.
 
END CLASS COMPREHENSIVE-SERVICE.

Multiple interfaces can be implemented by separating them with commas.

Common Use Cases

IMPLEMENTS is commonly used in specific scenarios where interface-based programming and polymorphic behavior are needed.

Service Layer Implementation

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* Service layer with interface implementation
INTERFACE-ID IDATABASE-SERVICE.
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-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.
 
END CLASS ORACLE-DATABASE-SERVICE.

Service layers use interfaces to provide consistent APIs.

Plugin Architecture

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* Plugin architecture with interface implementation
INTERFACE-ID IPLUGIN-INTERFACE.
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.

Polymorphic Behavior

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* Polymorphic behavior with interface implementation
IDENTIFICATION DIVISION.
PROGRAM-ID INTERFACE-DEMO.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  PAYMENT-PROCESSOR   OBJECT REFERENCE IPAYMENT-INTERFACE.
01  CREDIT-CARD-PROC    OBJECT REFERENCE CREDIT-CARD-PROCESSOR.
01  BANK-TRANSFER-PROC  OBJECT REFERENCE BANK-TRANSFER-PROCESSOR.
01  AMOUNT              PIC 9(8)V99 VALUE 100.50.
01  RESULT              PIC 9(4).
 
PROCEDURE DIVISION.
    * Create processor instances
    INVOKE CREDIT-CARD-PROCESSOR "NEW" RETURNING CREDIT-CARD-PROC
    INVOKE BANK-TRANSFER-PROCESSOR "NEW" RETURNING BANK-TRANSFER-PROC
    
    * Use credit card processor
    SET PAYMENT-PROCESSOR TO CREDIT-CARD-PROC
    INVOKE PAYMENT-PROCESSOR "PROCESS-PAYMENT" 
        USING AMOUNT RETURNING RESULT
    DISPLAY 'Credit Card Result: ' RESULT
    
    * Switch to bank transfer processor
    SET PAYMENT-PROCESSOR TO BANK-TRANSFER-PROC
    INVOKE PAYMENT-PROCESSOR "PROCESS-PAYMENT" 
        USING AMOUNT RETURNING RESULT
    DISPLAY 'Bank Transfer Result: ' RESULT
    
    STOP RUN.
 
END PROGRAM INTERFACE-DEMO.

Polymorphic behavior allows objects to be treated as interface instances.

Best Practices and Tips

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

IMPLEMENTS Design Principles

Complete implementation - Implement all interface methods
Method signature matching - Ensure exact parameter and return type matches
Interface segregation - Keep interfaces focused and cohesive
Documentation - Document interface contracts and implementations
Error handling - Implement proper error handling in interface methods
Testing - Test interface implementations thoroughly

Common Pitfalls to Avoid

Pitfall	Problem	Solution
Incomplete implementation	Compilation errors	Implement all interface methods
Signature mismatch	Method not recognized	Match interface method signatures exactly
Large interfaces	Difficult to implement	Keep interfaces small and focused
No error handling	Unreliable implementations	Implement proper error handling
Poor documentation	Confusion about contracts	Document interface requirements

Performance Considerations

Interface call overhead - Interface method calls may have slight overhead
Multiple interface implementation - Can increase class complexity
Memory footprint - Consider the memory usage of interface implementations
Method resolution - Interface method resolution may be slower than direct calls
Optimization opportunities - Some compilers optimize interface calls
Interface granularity - Balance flexibility with performance

When to Use IMPLEMENTS

Use Case	IMPLEMENTS 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

IMPLEMENTS Clause Quick Reference

Usage	Syntax	Example
Single interface	IMPLEMENTS interface-name	IMPLEMENTS IDATABASE-INTERFACE
Multiple interfaces	IMPLEMENTS interface1, interface2	IMPLEMENTS IFILE, ILOG, ISECURITY
With inheritance	INHERITS parent IMPLEMENTS interface	INHERITS BASE IMPLEMENTS IINTERFACE
Interface definition	INTERFACE-ID interface-name	INTERFACE-ID IPAYMENT-INTERFACE
Method definition	METHOD-ID method-name	METHOD-ID PROCESS-PAYMENT

Test Your Knowledge

1. What is the primary purpose of the IMPLEMENTS clause in COBOL?

To define class inheritance
To specify that a class implements interfaces
To create new objects
To define data structures

2. 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

3. How do you specify multiple interfaces in the IMPLEMENTS clause?

Use the AND keyword
Separate interface names with commas
Use multiple IMPLEMENTS clauses
Use the OR keyword

4. Which of the following is a benefit of using the IMPLEMENTS clause?

Reduced memory usage
Polymorphic behavior and code flexibility
Faster execution speed
Simpler syntax

5. What is the relationship between IMPLEMENTS and INHERITS?

They are the same thing
IMPLEMENTS is for interfaces, INHERITS is for classes
INHERITS is for interfaces, IMPLEMENTS is for classes
They cannot be used together

COBOL Tutorial

COBOL IMPLEMENTS Clause - Quick Reference

Overview

Purpose and Usage

Interface Implementation Flow

Syntax

Basic Syntax

Interface Definition

Multiple Interface Implementation

Common Use Cases

Service Layer Implementation

Plugin Architecture

Polymorphic Behavior

Best Practices and Tips

IMPLEMENTS Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use IMPLEMENTS

IMPLEMENTS Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

Related Concepts

INTERFACE-ID Clause

INHERITS Clause

CLASS-ID Clause

METHOD-ID Clause

Object-Oriented Programming

Related Pages

COBOL Tutorial

COBOL IMPLEMENTS Clause - Quick Reference

Overview

Purpose and Usage

Interface Implementation Flow

Syntax

Basic Syntax

Interface Definition

Multiple Interface Implementation

Common Use Cases

Service Layer Implementation

Plugin Architecture

Polymorphic Behavior

Best Practices and Tips

IMPLEMENTS Design Principles

Common Pitfalls to Avoid

Performance Considerations

When to Use IMPLEMENTS

IMPLEMENTS Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

What is the difference between IMPLEMENTS and INHERITS?

Can a class implement multiple interfaces?

Can interfaces inherit from other interfaces?

Is IMPLEMENTS supported in all COBOL dialects?

How do you test classes that implement interfaces?

Related Concepts

INTERFACE-ID Clause

INHERITS Clause

CLASS-ID Clause

METHOD-ID Clause

Object-Oriented Programming

Related Pages