State Pattern2026-05-14

Deep Dive: The State Pattern

The State Pattern is a behavioral design pattern that allows an object to change its behavior when its internal state changes.

Instead of a single class bloated with conditional logic (like giant if/else or switch statements), each state is encapsulated into its own class.

This promotes the Open/Closed Principle, allowing the addition of new states without modifying existing code.

In this vending machine implementation, the machine delegates all actions (inserting money, selecting products, and dispensing) to a current state object.

Transitions, such as moving from NoMoneyState to HasMoneyState or from DispenseState to SoldOutState, are handled dynamically by the state objects themselves.

Full Implementation

See Vending Machine LLD for the complete code implementation.