Template Method

• Defines the skeleton/template of an algorithm in an operation, deferring some steps to subclasses. This pattern lets subclasses redefine certain steps of an algorithm without changing the algorithm‘s structure.

Classical Structure

Scenario

• Build a banking app and report all user activities in audit trail. Every time user performs a task, report who did what and when within an audit trail

Problem

• Code duplication, every time you create a new task you have to follow the structure. Add private field AuditTrail and initialize in the constructor
• Developer should be forced to follow the structure which is missing

public class AuditTrail
{
    public void Record()
    {
        Console.WriteLine("Audit");
    }
}
public class GenerateReportTask
{
    AuditTrail auditTrail;

    public GenerateReportTask(AuditTrail auditTrail)
    {
        this.auditTrail = auditTrail;
    }

    public void Execute()
    {
        auditTrail.Record();

        Console.WriteLine("Generate report");
    }
}
public class TransferMoneyTask
{
    private AuditTrail auditTrail;

    public TransferMoneyTask(AuditTrail auditTrail)
    {
        this.auditTrail = auditTrail;
    }

    public void Execute()
    {
        auditTrail.Record();

        Console.WriteLine("Transfer money");
    }
}

Solution

public class AuditTrail
{
    public void Record()
    {
        Console.WriteLine("Audit");
    }
}
public abstract class Task
{
    private AuditTrail auditTrail;
    public Task()
    {
        auditTrail = new AuditTrail();
    }

    public void Execute()
    {
        auditTrail.Record();

        DoExecute();
    }

    protected abstract void DoExecute();
}
public class GenerateReportTask : Task
{
    protected override void DoExecute()
    {
        Console.WriteLine("Generate report");
    }
}
public class TransferMoneyTask: Task
{
    protected override void DoExecute()
    {
        Console.WriteLine("Transfer money");
    }
}
public class Program
{
    static void Main(string[] args)
    {
        var transferMoneyTask = new TransferMoneyTask();
        transferMoneyTask.Execute();

        var generateReportTask = new GenerateReportTask();
        generateReportTask.Execute();
    }
}

Example Structure

Example Code