COBOL Tutorial

COBOL METHOD Clause - Quick Reference

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Overview

The METHOD clause is used in object-oriented COBOL to define class methods that specify the behavior and functionality of objects. It enables encapsulation, inheritance, and polymorphism in COBOL applications, providing modern object-oriented programming capabilities.

Purpose and Usage

Class behavior - Define methods that belong to classes
Encapsulation - Control access to object data
Inheritance - Support method overriding in subclasses
Polymorphism - Enable different implementations
Object state - Access and modify object data

Object-Oriented Concept

Class Definition: Contains data and methods

Method Definition: Specifies behavior

Object Creation: Instances of classes

Method Invocation: Using INVOKE statement

Inheritance: Subclasses inherit methods

The METHOD clause enables object-oriented programming in COBOL.

Syntax and Usage

The METHOD clause is defined within class definitions in the PROCEDURE DIVISION, specifying the behavior and functionality of class methods.

Basic Syntax

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* Basic METHOD clause syntax
METHOD-ID. method-name [USING parameter-list].
 
* Examples
METHOD-ID. CALCULATE-AREA USING LENGTH, WIDTH.
METHOD-ID. GET-BALANCE.
METHOD-ID. UPDATE-STATUS USING NEW-STATUS.
 
* Complete example
CLASS-ID. BANK-ACCOUNT.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01  ACCOUNT-BALANCE    PIC 9(10)V99.
01  ACCOUNT-STATUS     PIC X(10).
 
PROCEDURE DIVISION.
METHOD-ID. DEPOSIT USING AMOUNT.
    ADD AMOUNT TO ACCOUNT-BALANCE
    MOVE "ACTIVE" TO ACCOUNT-STATUS
END METHOD.
 
METHOD-ID. WITHDRAW USING AMOUNT.
    IF ACCOUNT-BALANCE >= AMOUNT
        SUBTRACT AMOUNT FROM ACCOUNT-BALANCE
        MOVE "ACTIVE" TO ACCOUNT-STATUS
    ELSE
        MOVE "INSUFFICIENT" TO ACCOUNT-STATUS
    END-IF
END METHOD.
 
METHOD-ID. GET-BALANCE.
    * Return current balance
    * Implementation here
END METHOD.

Methods are defined within class definitions using METHOD-ID.

Complete Example

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* Complete object-oriented COBOL example
       CLASS-ID. CUSTOMER.
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  CUSTOMER-DATA.
           05  CUSTOMER-ID        PIC 9(6).
           05  CUSTOMER-NAME      PIC X(30).
           05  CUSTOMER-EMAIL     PIC X(50).
           05  CUSTOMER-STATUS    PIC X(10).
           05  CUSTOMER-BALANCE   PIC 9(8)V99.
       
       LINKAGE SECTION.
       01  PARAMETER-AREA.
           05  INPUT-PARAM        PIC X(30).
           05  OUTPUT-PARAM       PIC X(50).
       
       PROCEDURE DIVISION.
       
       METHOD-ID. INITIALIZE-CUSTOMER USING CUST-ID, CUST-NAME, CUST-EMAIL.
           MOVE CUST-ID TO CUSTOMER-ID
           MOVE CUST-NAME TO CUSTOMER-NAME
           MOVE CUST-EMAIL TO CUSTOMER-EMAIL
           MOVE "ACTIVE" TO CUSTOMER-STATUS
           MOVE ZERO TO CUSTOMER-BALANCE
       END METHOD.
       
       METHOD-ID. UPDATE-BALANCE USING NEW-BALANCE.
           MOVE NEW-BALANCE TO CUSTOMER-BALANCE
           IF CUSTOMER-BALANCE < 0
               MOVE "OVERDRAWN" TO CUSTOMER-STATUS
           ELSE
               MOVE "ACTIVE" TO CUSTOMER-STATUS
           END-IF
       END METHOD.
       
       METHOD-ID. GET-CUSTOMER-INFO RETURNING CUST-INFO.
           MOVE CUSTOMER-DATA TO CUST-INFO
       END METHOD.
       
       METHOD-ID. VALIDATE-EMAIL.
           * Email validation logic here
           IF CUSTOMER-EMAIL CONTAINS "@"
               MOVE "VALID" TO CUSTOMER-STATUS
           ELSE
               MOVE "INVALID" TO CUSTOMER-STATUS
           END-IF
       END METHOD.
       
       END CLASS.

This example shows a complete class with multiple methods.

Method Invocation

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* Method invocation examples
       IDENTIFICATION DIVISION.
       PROGRAM-ID. METHOD-DEMO.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  CUSTOMER-OBJECT    OBJECT REFERENCE CUSTOMER.
       01  CUST-ID            PIC 9(6) VALUE 123456.
       01  CUST-NAME          PIC X(30) VALUE "John Doe".
       01  CUST-EMAIL         PIC X(50) VALUE "john@example.com".
       01  NEW-BALANCE        PIC 9(8)V99 VALUE 1000.00.
       01  CUST-INFO          PIC X(100).
       
       PROCEDURE DIVISION.
       MAIN-LOGIC.
           * Create customer object
           INVOKE CUSTOMER "NEW" RETURNING CUSTOMER-OBJECT
           
           * Initialize customer
           INVOKE CUSTOMER-OBJECT "INITIALIZE-CUSTOMER" 
               USING CUST-ID, CUST-NAME, CUST-EMAIL
           
           * Update balance
           INVOKE CUSTOMER-OBJECT "UPDATE-BALANCE" 
               USING NEW-BALANCE
           
           * Get customer info
           INVOKE CUSTOMER-OBJECT "GET-CUSTOMER-INFO" 
               RETURNING CUST-INFO
           
           * Validate email
           INVOKE CUSTOMER-OBJECT "VALIDATE-EMAIL"
           
           STOP RUN.

Methods are invoked using the INVOKE statement with object references.

Common Use Cases

The METHOD clause is essential in various scenarios where object-oriented programming is needed for better code organization and maintainability.

Business Object Modeling

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* Business object modeling with methods
       CLASS-ID. BANK-ACCOUNT.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  ACCOUNT-DATA.
           05  ACCOUNT-NUMBER    PIC 9(10).
           05  ACCOUNT-TYPE      PIC X(10).
           05  ACCOUNT-BALANCE   PIC 9(10)V99.
           05  ACCOUNT-STATUS    PIC X(10).
           05  LAST-TRANSACTION  PIC 9(8).
       
       PROCEDURE DIVISION.
       
       METHOD-ID. OPEN-ACCOUNT USING ACC-NUM, ACC-TYPE, INITIAL-DEPOSIT.
           MOVE ACC-NUM TO ACCOUNT-NUMBER
           MOVE ACC-TYPE TO ACCOUNT-TYPE
           MOVE INITIAL-DEPOSIT TO ACCOUNT-BALANCE
           MOVE "ACTIVE" TO ACCOUNT-STATUS
           MOVE FUNCTION CURRENT-DATE TO LAST-TRANSACTION
       END METHOD.
       
       METHOD-ID. DEPOSIT USING AMOUNT.
           IF ACCOUNT-STATUS = "ACTIVE"
               ADD AMOUNT TO ACCOUNT-BALANCE
               MOVE FUNCTION CURRENT-DATE TO LAST-TRANSACTION
           END-IF
       END METHOD.
       
       METHOD-ID. WITHDRAW USING AMOUNT RETURNING SUCCESS-FLAG.
           IF ACCOUNT-STATUS = "ACTIVE" AND ACCOUNT-BALANCE >= AMOUNT
               SUBTRACT AMOUNT FROM ACCOUNT-BALANCE
               MOVE FUNCTION CURRENT-DATE TO LAST-TRANSACTION
               MOVE "Y" TO SUCCESS-FLAG
           ELSE
               MOVE "N" TO SUCCESS-FLAG
           END-IF
       END METHOD.
       
       METHOD-ID. GET-STATEMENT RETURNING STATEMENT-DATA.
           * Generate account statement
           * Implementation here
       END METHOD.
       
       END CLASS.

Business objects use methods to encapsulate business logic and data.

Data Validation

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* Data validation with methods
       CLASS-ID. DATA-VALIDATOR.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  VALIDATION-RULES.
           05  MIN-LENGTH        PIC 9(2) VALUE 3.
           05  MAX-LENGTH        PIC 9(2) VALUE 50.
           05  ALLOWED-CHARS     PIC X(62) VALUE 
               "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789".
       
       PROCEDURE DIVISION.
       
       METHOD-ID. VALIDATE-EMAIL USING EMAIL-ADDRESS RETURNING IS-VALID.
           * Email validation logic
           IF EMAIL-ADDRESS CONTAINS "@" AND EMAIL-ADDRESS CONTAINS "."
               MOVE "Y" TO IS-VALID
           ELSE
               MOVE "N" TO IS-VALID
           END-IF
       END METHOD.
       
       METHOD-ID. VALIDATE-PHONE USING PHONE-NUMBER RETURNING IS-VALID.
           * Phone number validation
           IF PHONE-NUMBER IS NUMERIC AND LENGTH OF PHONE-NUMBER = 10
               MOVE "Y" TO IS-VALID
           ELSE
               MOVE "N" TO IS-VALID
           END-IF
       END METHOD.
       
       METHOD-ID. VALIDATE-NAME USING NAME-VALUE RETURNING IS-VALID.
           * Name validation
           IF LENGTH OF NAME-VALUE >= MIN-LENGTH AND 
              LENGTH OF NAME-VALUE <= MAX-LENGTH
               MOVE "Y" TO IS-VALID
           ELSE
               MOVE "N" TO IS-VALID
           END-IF
       END METHOD.
       
       END CLASS.

Data validation uses methods to encapsulate validation logic.

Inheritance and Polymorphism

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* Inheritance and polymorphism with methods
       CLASS-ID. EMPLOYEE.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  EMPLOYEE-DATA.
           05  EMPLOYEE-ID       PIC 9(6).
           05  EMPLOYEE-NAME     PIC X(30).
           05  BASE-SALARY       PIC 9(8)V99.
       
       PROCEDURE DIVISION.
       
       METHOD-ID. CALCULATE-SALARY RETURNING TOTAL-SALARY.
           MOVE BASE-SALARY TO TOTAL-SALARY
       END METHOD.
       
       END CLASS.
       
       CLASS-ID. MANAGER INHERITS FROM EMPLOYEE.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  MANAGER-DATA.
           05  BONUS-AMOUNT      PIC 9(8)V99.
       
       PROCEDURE DIVISION.
       
       METHOD-ID. CALCULATE-SALARY RETURNING TOTAL-SALARY.
           * Override parent method
           INVOKE SUPER "CALCULATE-SALARY" RETURNING TOTAL-SALARY
           ADD BONUS-AMOUNT TO TOTAL-SALARY
       END METHOD.
       
       METHOD-ID. SET-BONUS USING BONUS.
           MOVE BONUS TO BONUS-AMOUNT
       END METHOD.
       
       END CLASS.

Inheritance allows subclasses to override parent methods.

Best Practices and Tips

Following these best practices ensures effective use of the METHOD clause in object-oriented COBOL applications.

METHOD Clause Best Practices

Use descriptive names - Name methods clearly to indicate their purpose
Follow naming conventions - Use consistent naming patterns for methods
Keep methods focused - Each method should have a single responsibility
Use proper encapsulation - Control access to object data through methods
Document method behavior - Clearly document what each method does
Handle errors appropriately - Include proper error handling in methods

Method Design Patterns

Pattern	Description	Example
Getter/Setter	Access and modify object data	GET-BALANCE, SET-BALANCE
Constructor	Initialize object state	INITIALIZE-ACCOUNT
Validator	Validate data or state	VALIDATE-EMAIL
Processor	Process data or perform operations	CALCULATE-INTEREST
Formatter	Format data for display	FORMAT-STATEMENT

Performance Considerations

Method overhead - Method calls have some performance overhead
Object creation - Creating objects consumes memory
Inheritance depth - Deep inheritance hierarchies can impact performance
Parameter passing - Large parameters can affect performance
Memory management - Objects need proper cleanup
Testing - Test method performance with large datasets

When to Use METHOD Clause

Use Case	METHOD Suitability	Reasoning
Object-oriented design	Excellent	Core feature of OO programming
Code reuse	Excellent	Enables inheritance and polymorphism
Encapsulation	Excellent	Controls access to object data
Simple procedures	Poor	Use traditional COBOL procedures
Legacy systems	Poor	May not support OO features

METHOD Clause Quick Reference

Usage	Syntax	Example
Basic method	METHOD-ID. method-name.	METHOD-ID. GET-BALANCE.
Method with parameters	METHOD-ID. method-name USING param.	METHOD-ID. DEPOSIT USING AMOUNT.
Method with return value	METHOD-ID. method-name RETURNING value.	METHOD-ID. CALCULATE RETURNING RESULT.
Method invocation	INVOKE object "method" USING params	INVOKE ACCOUNT "DEPOSIT" USING 100
Constructor method	METHOD-ID. NEW.	METHOD-ID. NEW.

Test Your Knowledge

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

To define data structures
To define class methods in object-oriented COBOL
To control file operations
To perform arithmetic calculations

2. In which COBOL division is the METHOD clause typically defined?

IDENTIFICATION DIVISION
ENVIRONMENT DIVISION
DATA DIVISION
PROCEDURE DIVISION

3. How is the METHOD clause used in object-oriented COBOL?

To define data fields
To define class behavior and functionality
To control program flow
To manage memory allocation

4. Which of the following is a common use case for the METHOD clause?

File I/O operations
Defining class behavior and encapsulation
Data validation
Mathematical calculations

5. How do you invoke a method defined with the METHOD clause?

Using CALL statement
Using INVOKE statement with object reference
Using PERFORM statement
Using GO TO statement

COBOL Tutorial

COBOL METHOD Clause - Quick Reference

Overview

Purpose and Usage

Object-Oriented Concept

Syntax and Usage

Basic Syntax

Complete Example

Method Invocation

Common Use Cases

Business Object Modeling

Data Validation

Inheritance and Polymorphism

Best Practices and Tips

METHOD Clause Best Practices

Method Design Patterns

Performance Considerations

When to Use METHOD Clause

METHOD Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

Related Concepts

Object-Oriented COBOL

CLASS-ID Clause

INVOKE Statement

Inheritance

Encapsulation

Related Pages

COBOL Tutorial

COBOL METHOD Clause - Quick Reference

Overview

Purpose and Usage

Object-Oriented Concept

Syntax and Usage

Basic Syntax

Complete Example

Method Invocation

Common Use Cases

Business Object Modeling

Data Validation

Inheritance and Polymorphism

Best Practices and Tips

METHOD Clause Best Practices

Method Design Patterns

Performance Considerations

When to Use METHOD Clause

METHOD Clause Quick Reference

Test Your Knowledge

Frequently Asked Questions

What is the difference between METHOD and FUNCTION in COBOL?

How do you define parameters for a METHOD in COBOL?

Can a METHOD access object data in COBOL?

How does the METHOD clause support inheritance in COBOL?

What are the benefits of using METHODS in COBOL?

Related Concepts

Object-Oriented COBOL

CLASS-ID Clause

INVOKE Statement

Inheritance

Encapsulation

Related Pages