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COBOL Tutorial

COBOL CLASS-ID - Quick Reference

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Overview

CLASS-ID is a COBOL keyword used in object-oriented programming to define a class. It marks the beginning of a class definition and is followed by the class name, enabling the creation of classes with methods, properties, and other object-oriented features in COBOL.

Purpose and Usage

  • Object-oriented programming in COBOL
  • Class definition and organization
  • Method and property encapsulation
  • Inheritance and polymorphism
  • Code reusability and modularity

Syntax

CLASS-ID follows specific syntax patterns for class definitions:

Basic CLASS-ID Syntax

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* Basic CLASS-ID syntax
CLASS-ID. ClassName.
OBJECT SECTION.
CLASS ClassName.
    * Class data declarations
    01  class-data PIC X(50).
    
    * Method definitions
    METHOD-ID. methodName.
    DATA DIVISION.
    LINKAGE SECTION.
        01  parameter PIC X(20).
    PROCEDURE DIVISION USING parameter.
        * Method implementation
        DISPLAY "Method called with: " parameter.
        EXIT METHOD.
    END METHOD methodName.
    
END CLASS ClassName.
 
* CLASS-ID with inheritance
CLASS-ID. SubClass INHERITS FROM SuperClass.
OBJECT SECTION.
CLASS SubClass.
    * Subclass implementation
    METHOD-ID. newMethod.
    PROCEDURE DIVISION.
        * Method implementation
        EXIT METHOD.
    END METHOD newMethod.
    
END CLASS SubClass.

CLASS-ID defines classes with methods and properties in object-oriented COBOL.

Class Structure Components

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* Complete class structure
CLASS-ID. CustomerClass.
OBJECT SECTION.
CLASS CustomerClass.
    * Class properties (data)
    01  customer-id PIC X(10).
    01  customer-name PIC X(50).
    01  customer-email PIC X(100).
    
    * Constructor method
    METHOD-ID. NEW.
    DATA DIVISION.
    LINKAGE SECTION.
        01  id PIC X(10).
        01  name PIC X(50).
        01  email PIC X(100).
    PROCEDURE DIVISION USING id, name, email.
        MOVE id TO customer-id.
        MOVE name TO customer-name.
        MOVE email TO customer-email.
        EXIT METHOD.
    END METHOD NEW.
    
    * Getter methods
    METHOD-ID. getCustomerId.
    DATA DIVISION.
    LINKAGE SECTION.
        01  return-id PIC X(10).
    PROCEDURE DIVISION RETURNING return-id.
        MOVE customer-id TO return-id.
        EXIT METHOD.
    END METHOD getCustomerId.
    
    * Setter methods
    METHOD-ID. setCustomerName.
    DATA DIVISION.
    LINKAGE SECTION.
        01  new-name PIC X(50).
    PROCEDURE DIVISION USING new-name.
        MOVE new-name TO customer-name.
        EXIT METHOD.
    END METHOD setCustomerName.
    
END CLASS CustomerClass.

Practical Examples

Here are some practical uses of CLASS-ID in COBOL:

Customer Management Class

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* Customer management class
CLASS-ID. CustomerManager.
OBJECT SECTION.
CLASS CustomerManager.
    * Customer data
    01  customer-list OCCURS 100 TIMES.
        05  customer-id PIC X(10).
        05  customer-name PIC X(50).
        05  customer-email PIC X(100).
    01  customer-count PIC 9(3) VALUE 0.
    
    * Add customer method
    METHOD-ID. addCustomer.
    DATA DIVISION.
    LINKAGE SECTION.
        01  id PIC X(10).
        01  name PIC X(50).
        01  email PIC X(100).
    PROCEDURE DIVISION USING id, name, email.
        IF customer-count < 100
            ADD 1 TO customer-count
            MOVE id TO customer-id(customer-count)
            MOVE name TO customer-name(customer-count)
            MOVE email TO customer-email(customer-count)
            DISPLAY "Customer added successfully"
        ELSE
            DISPLAY "Customer list is full"
        END-IF.
        EXIT METHOD.
    END METHOD addCustomer.
    
    * Find customer method
    METHOD-ID. findCustomer.
    DATA DIVISION.
    LINKAGE SECTION.
        01  search-id PIC X(10).
        01  found-name PIC X(50).
        01  found-email PIC X(100).
        01  found-flag PIC X VALUE "N".
    PROCEDURE DIVISION USING search-id, found-name, found-email, found-flag.
        PERFORM VARYING customer-index FROM 1 BY 1
            UNTIL customer-index > customer-count
            IF customer-id(customer-index) = search-id
                MOVE customer-name(customer-index) TO found-name
                MOVE customer-email(customer-index) TO found-email
                MOVE "Y" TO found-flag
                EXIT PERFORM
            END-IF
        END-PERFORM.
        EXIT METHOD.
    END METHOD findCustomer.
    
    * Get customer count method
    METHOD-ID. getCustomerCount.
    DATA DIVISION.
    LINKAGE SECTION.
        01  count PIC 9(3).
    PROCEDURE DIVISION RETURNING count.
        MOVE customer-count TO count.
        EXIT METHOD.
    END METHOD getCustomerCount.
    
END CLASS CustomerManager.

Customer management class with methods for adding and finding customers.

Bank Account Class

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* Bank account class with inheritance
CLASS-ID. BankAccount.
OBJECT SECTION.
CLASS BankAccount.
    * Account properties
    01  account-number PIC X(10).
    01  account-holder PIC X(50).
    01  balance PIC 9(10)V99 VALUE 0.00.
    
    * Constructor
    METHOD-ID. NEW.
    DATA DIVISION.
    LINKAGE SECTION.
        01  number PIC X(10).
        01  holder PIC X(50).
    PROCEDURE DIVISION USING number, holder.
        MOVE number TO account-number.
        MOVE holder TO account-holder.
        EXIT METHOD.
    END METHOD NEW.
    
    * Deposit method
    METHOD-ID. deposit.
    DATA DIVISION.
    LINKAGE SECTION.
        01  amount PIC 9(10)V99.
    PROCEDURE DIVISION USING amount.
        ADD amount TO balance.
        DISPLAY "Deposited: " amount " New balance: " balance.
        EXIT METHOD.
    END METHOD deposit.
    
    * Withdraw method
    METHOD-ID. withdraw.
    DATA DIVISION.
    LINKAGE SECTION.
        01  amount PIC 9(10)V99.
        01  success PIC X VALUE "N".
    PROCEDURE DIVISION USING amount RETURNING success.
        IF balance >= amount
            SUBTRACT amount FROM balance
            MOVE "Y" TO success
            DISPLAY "Withdrawn: " amount " New balance: " balance
        ELSE
            DISPLAY "Insufficient funds"
            MOVE "N" TO success
        END-IF.
        EXIT METHOD.
    END METHOD withdraw.
    
    * Get balance method
    METHOD-ID. getBalance.
    DATA DIVISION.
    LINKAGE SECTION.
        01  current-balance PIC 9(10)V99.
    PROCEDURE DIVISION RETURNING current-balance.
        MOVE balance TO current-balance.
        EXIT METHOD.
    END METHOD getBalance.
    
END CLASS BankAccount.
 
* Savings account subclass
CLASS-ID. SavingsAccount INHERITS FROM BankAccount.
OBJECT SECTION.
CLASS SavingsAccount.
    * Interest rate
    01  interest-rate PIC 9(3)V99 VALUE 2.50.
    
    * Add interest method
    METHOD-ID. addInterest.
    PROCEDURE DIVISION.
        COMPUTE balance = balance + (balance * interest-rate / 100).
        DISPLAY "Interest added. New balance: " balance.
        EXIT METHOD.
    END METHOD addInterest.
    
END CLASS SavingsAccount.

Bank account class with inheritance for savings accounts.

Best Practices

  • Use meaningful class names that describe the purpose of the class.
  • Encapsulate data and provide getter/setter methods for access.
  • Use inheritance to create class hierarchies when appropriate.
  • Implement constructors to initialize class data properly.
  • Document class methods and their parameters clearly.
  • Follow object-oriented design principles.

Common Pitfalls

  • Not properly initializing class data in constructors.
  • Creating overly complex class hierarchies.
  • Not providing appropriate access methods for class data.
  • Mixing procedural and object-oriented programming styles.
  • Not documenting class interfaces and method purposes.

Test Your Knowledge

1. What is CLASS-ID in COBOL?

  • A data type
  • A class identifier for object-oriented programming
  • A file operation
  • A program structure

2. What does CLASS-ID define?

  • A data structure
  • A class with methods and properties
  • A file definition
  • A program section

3. Where is CLASS-ID typically used?

  • In procedural COBOL
  • In object-oriented COBOL
  • In file processing
  • In data declarations

4. What follows CLASS-ID in a class definition?

  • Data declarations
  • Class name and object section
  • File definitions
  • Procedure division

5. What is the primary benefit of using CLASS-ID?

  • Faster execution
  • Object-oriented programming capabilities
  • Better file handling
  • Improved data storage

Frequently Asked Questions

Related Concepts

Object-Oriented COBOL

Object-oriented programming in COBOL.

METHOD-ID

Defining methods in COBOL classes.

Inheritance

Class inheritance in COBOL.

Encapsulation

Data encapsulation in COBOL.

Program Structure

Understanding COBOL program structure.

BOOLEANCONDITION