Adapter Pattern – Implementation [Object Adapter]

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Introduction

The Adapter Design Pattern allows incompatible interfaces to work together without modifying existing code. There are two primary approaches to implement this pattern: Object Adapter (using composition) and Class Adapter (using inheritance). In this tutorial, we implement the Object Adapter pattern using a real-world scenario where an existing Human Resource (HR) System integrates with a Third-Party Billing System.

The Incompatibility Problem

• Client (HR System): Supplies employee details in a two-dimensional String[][] array format.
• Adaptee (Third-Party Billing System): Only accepts a List<Employee> in its processSalary() method.

Neither codebase should be altered. In the Object Adapter approach, the adapter holds a reference (composition) to the adaptee instance, converts the String[][] array into a List<Employee>, and delegates the call.

Object Adapter Role Mapping

Pattern Role	Component in Example	Role Description
Client	HumanResourceSystem	Provides employee records as a String[][]
Target Interface	ITarget	Declares processCompanySalary(String[][])
Adaptee	ThirdPartyBillingSystem	Provides processSalary(List<Employee>)
Object Adapter	EmployeeAdapter	Implements ITarget and holds a reference to ThirdPartyBillingSystem

Step-by-Step Java Implementation

1. The Employee Model Class

public class Employee {
    private int empId;
    private String name;
    private String designation;

    public Employee(int empId, String name, String designation) {
        this.empId = empId;
        this.name = name;
        this.designation = designation;
    }

    public int getEmpId() { return empId; }
    public String getName() { return name; }
    public String getDesignation() { return designation; }
}

2. Adaptee: ThirdPartyBillingSystem

import java.util.List;

public class ThirdPartyBillingSystem {
    public void processSalary(List<Employee> employeeList) {
        for (Employee emp : employeeList) {
            int salary = 0;
            if ("Team Leader".equalsIgnoreCase(emp.getDesignation())) {
                salary = 70000;
            } else if ("Developer".equalsIgnoreCase(emp.getDesignation())) {
                salary = 40000;
            } else if ("Tester".equalsIgnoreCase(emp.getDesignation())) {
                salary = 30000;
            }
            System.out.println("Credited Rs. " + salary + " to " + emp.getName() + " (" + emp.getDesignation() + ")");
        }
    }
}

3. Target Interface: ITarget

public interface ITarget {
    void processCompanySalary(String[][] employeesArray);
}

4. Object Adapter: EmployeeAdapter

Notice how EmployeeAdapter maintains an instance variable reference (composition) to ThirdPartyBillingSystem:

import java.util.ArrayList;
import java.util.List;

public class EmployeeAdapter implements ITarget {

    // Object composition: holds a reference to the Adaptee
    private ThirdPartyBillingSystem thirdPartyBillingSystem = new ThirdPartyBillingSystem();

    @Override
    public void processCompanySalary(String[][] employeesArray) {
        List<Employee> employeeList = new ArrayList<>();

        for (String[] empData : employeesArray) {
            int id = Integer.parseInt(empData[0]);
            String name = empData[1];
            String designation = empData[2];
            employeeList.add(new Employee(id, name, designation));
        }

        // Delegate to the composed Adaptee instance
        thirdPartyBillingSystem.processSalary(employeeList);
    }
}

5. Client: HumanResourceSystem

public class HumanResourceSystem {

    public static String[][] getEmployees() {
        return new String[][] {
            {"101", "Dave", "Team Leader"},
            {"102", "Peter", "Developer"},
            {"103", "Raj", "Developer"},
            {"104", "Rahul", "Tester"}
        };
    }

    public static void main(String[] args) {
        ITarget target = new EmployeeAdapter();
        String[][] employeesArray = getEmployees();
        
        System.out.println("HR System passing employee array to adapter...\n");
        target.processCompanySalary(employeesArray);
    }
}

Console Output

HR System passing employee array to adapter...

Credited Rs. 70000 to Dave (Team Leader)
Credited Rs. 40000 to Peter (Developer)
Credited Rs. 40000 to Raj (Developer)
Credited Rs. 30000 to Rahul (Tester)

Related Tutorials from Ram N Java

• Adapter Design Pattern Implementation: Class Adapter Example
• Adapter Design Pattern Implementation: Mobile Charger Example
• Adapter Design Pattern in Action: Real-World JDBC Driver Example
• Adapter Design Pattern: Class Diagram Overview

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Adapter Pattern – Implementation [Object Adapter]

Adapter Pattern – Implementation [Object Adapter] - Class Diagram

Employee.java

public class Employee
{
private int    empId;
private String name;
private String designation;

public Employee( int empId, String name, String designation )
{
super();
this.empId = empId;
this.name = name;
this.designation = designation;
}

public int getEmpId()
{
return empId;
}

public void setEmpId( int empId )
{
this.empId = empId;
}

public String getName()
{
return name;
}

public void setName( String name )
{
this.name = name;
}

public String getDesignation()
{
return designation;
}

public void setDesignation( String designation )
{
this.designation = designation;
}

@Override
public String toString()
{
return "Employee [empId=" + empId + ", name=" + name + ", designation=" + designation + "]";
}

}

ThirdPartyBillingSystem.java

import java.util.ArrayList;

/*
 * ThirdPartyBillingSystem accepts employees information as a List to process each employee salary
 */
public class ThirdPartyBillingSystem
{
public void processSalary( ArrayList<Employee> employeeList )
{
for( Employee employee : employeeList )
{
System.out.print("\n"+employee.toString()+" : ");
if( employee.getDesignation().equalsIgnoreCase("Team Leader") )
{
System.out.println("70000Rs Salary credited to " + employee.getName() + " Account\n");
}
else if( employee.getDesignation().equalsIgnoreCase("Developer") )
{
System.out.println("40000Rs Salary credited to " + employee.getName() + " Account\n");
}
else if( employee.getDesignation().equalsIgnoreCase("Tester") )
{
System.out.println("30000Rs Salary credited to " + employee.getName() + " Account\n");
}
}
}

}

ITarget.java

public interface ITarget
{
public void processCompanySalary(String[][] employeeInfo);
}

EmployeeAdapter.java

import java.util.ArrayList;

public class EmployeeAdapter implements ITarget
{
ThirdPartyBillingSystem thirdPartyBillingSystem =new ThirdPartyBillingSystem();

/*
* This Adapter method converts String Array employee information to ArrayList of Employees
*
*/

@Override
public void processCompanySalary( String[][] employeeInfo )
{
String empId = null;
String name = null;
String designation = null;
ArrayList<Employee> employeeList = new ArrayList<Employee>();
for( int i = 0; i < employeeInfo.length; i++ )
{

for( int j = 0; j < employeeInfo[i].length; j++ )
{
if( j == 0 )
{
empId = employeeInfo[i][j];
}
else if( j == 1 )
{
name = employeeInfo[i][j];
}
else
{
designation = employeeInfo[i][j];
}
}
employeeList.add(new Employee(Integer.parseInt(empId), name, designation));

}

System.out.println("Adapter converted Array of Employee to ArrayList of Employee : \n"+employeeList+"\n"+
"then delegate to the ThirdPartyBillingSystem for processing the employee salary");
thirdPartyBillingSystem.processSalary(employeeList);


}

}

HumanResourceSystem.java

/*
 * Client System which has employee information as String Array
 *
 */

public class HumanResourceSystem
{

public static String[][] getEmployees()
{
String[][] employees = new String[4][];

employees[0] = new String[] { "100", "Dave", "Team Leader" };
employees[1] = new String[] { "101", "Ram", "Developer" };
employees[2] = new String[] { "102", "Raj", "Developer" };
employees[3] = new String[] { "103", "Rahul", "Tester" };

return employees;
}

public static void main( String args[] )
{

ITarget target = new EmployeeAdapter();
System.out.println("HR system passes employee string array to Adapter\n");
target.processCompanySalary(getEmployees());

}
}

Output

HR system passes employee string array to Adapter

Adapter converted Array of Employee to ArrayList of Employee :
[Employee [empId=100, name=Dave, designation=Team Leader], Employee [empId=101, name=Ram, designation=Developer], Employee [empId=102, name=Raj, designation=Developer], Employee [empId=103, name=Rahul, designation=Tester]]
then delegate to the ThirdPartyBillingSystem for processing the employee salary

Employee [empId=100, name=Dave, designation=Team Leader] : 70000Rs Salary credited to Dave Account


Employee [empId=101, name=Ram, designation=Developer] : 40000Rs Salary credited to Ram Account


Employee [empId=102, name=Raj, designation=Developer] : 40000Rs Salary credited to Raj Account


Employee [empId=103, name=Rahul, designation=Tester] : 30000Rs Salary credited to Rahul Account


See also:

Adapter Design pattern - Introduction

Adapter Design Pattern - Real Time Exmaple(Translator)

Adapter Design pattern - Real Time Example (Card Reader)

Adapter Design pattern - Real Time Example (Mobile Charger)

Adapter Design pattern - Real Time Example (Universal Adaptor)

Adapter Design pattern - Real Time Example [JDBC Driver]

Adapter Design pattern - Class diagram

Adapter Design Pattern - Sequence diagram

Adapter Design Pattern - Implementation [Language Translator]

Adapter Pattern - Implementation [Class Adapter]

Adapter Design Pattern - Implementation [Mobile Charger]

Adapter Design Pattern - Key Points

All Design Patterns Links