Behavioral Design Pattern

State Design Pattern in Java

Allow an object to change its behavior when its internal state changes.

In this lesson: State moves state-specific behavior into separate objects. The context delegates work to the current state instead of growing a large conditional statement.

Overview

State is useful when its recurring design problem appears in a real application. It keeps the relevant responsibilities organized while allowing surrounding code to depend on clear abstractions.

Implementation

interface OrderState { void next(Order order); }
final class Order { private OrderState state; Order(OrderState state) { this.state = state; } void next() { state.next(this); } void state(OrderState state) { this.state = state; } }

final class NewOrder implements OrderState { public void next(Order order) { order.state(new ShippedOrder()); } }
final class ShippedOrder implements OrderState { public void next(Order order) { System.out.println("Delivered"); } }

When should you use it?

Use State for order workflows, connection lifecycles, media players, and other objects whose behavior changes across well-defined states.

Next step: Continue with the Design Patterns course and explore the next pattern.