Creational Patterns

Creational patterns provide various object creation mechanisms, which increase flexibility and reuse of existing code.

Patterns in this Category

Singleton

Ensures a class has only one instance and provides global access to it.

• Interview Examples:

  • Database Connection Pool manager.

  • Application Configuration Manager (e.g., reading application.properties).

  • Logger service, caching service instance shared across the application.

• Java Implementation:

  • class with a private constructor and a public static global access method (with double-checked locking).

  • Alternatively, robustly implemented using an enum.

Factory Method

Defines an interface for creating objects but lets subclasses decide which class to instantiate.

• Interview Examples:

  • Logistics management where a Transport factory creates Truck or Ship.

  • Database connection driver factory treating MySQL, PostgreSQL, or Oracle instances interchangeably.

  • Document creator where WordConverter creates .docx and PDFConverter creates .pdf.

• Java Implementation:

  • interface or abstract class for the Creator declaring an abstract create() method.

  • class for Concrete Creators implementing the factory method.

Abstract Factory

Provides an interface for creating families of related objects without specifying concrete classes.

• Interview Examples:

  • Cross-platform UI toolkit (Windows/Mac button and checkbox creation).

  • Car manufacturing system producing a family of parts (Engine, Tires) for different car models (Sports, SUV).

• Java Implementation:

  • interface for the Abstract Factory predicting family creation methods.

  • interface for each Abstract Product family.

Builder

Constructs complex objects step by step, allowing different representations using the same construction process.

• Interview Examples:

  • Constructing an HTTP Request object or a SQL Query builder.

  • Meal ordering in a restaurant where a meal consists of various configurable parts (Burger, Drink, Toy).

  • Designing a customizable computer (CPU, RAM, Storage).

• Java Implementation:

  • class or interface for the Builder with chainable methods (returning this).

  • Often implemented as a public static class nested within the Target Product class.

Prototype

Creates new objects by cloning existing objects, avoiding expensive initialization.

• Interview Examples:

  • Copy-pasting elements in a graphic editor.

  • Spawning enemy NPCs in a game based on a base template.

  • Caching frequently used complex configuration objects to avoid repeated database hits.

• Java Implementation:

  • interface extending Java's Cloneable or providing a custom clone() method.

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When to Use Creational Patterns

• When object creation is complex or resource-intensive

• When you need to decouple object creation from usage

• When you want to control object instantiation

• When you need families of related objects