Template Method

Context: Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps without changing the algorithm’s structure.

public abstract class AbstractClass
{
    public void TemplateMethod()
    {
        Step1();
        Step2();
    }
    protected abstract void Step1();
    protected virtual void Step2() => Console.WriteLine("Default step2");
}

public class ConcreteClass : AbstractClass
{
    protected override void Step1() => Console.WriteLine("Step1 implemented");
}

Real-world usage example

Data importers: A base DataImporter defines steps: OpenSource(), ParseData(), ValidateData(), SaveToDatabase(). Subclasses override only needed steps (CSV importer, XML importer, JSON importer).

Example: In .NET, Stream.Read is abstract; concrete streams override it. IDisposable pattern with Dispose(bool) is a template method. Also, System.Web.UI.Page life cycle methods.

Related sections

• 5.3 Behavioural patterns
• 5.3.7 State
• 5.3.9 Visitor