State / Control• Patterns: State, Singleton

Traffic Signal

Easy

Problem Summary

Design a Traffic Signal Controller that transitions between Red, Yellow, and Green states with dynamic durations.

Functional Scope

Maintain active signal light status (Red, Yellow, Green).
Process state transitions sequentially: Red -> Green -> Yellow -> Red.
Allow dynamic duration override configurations for active states.

Entity-Relationship (ER) Schema

TrafficSignalController [1] <---> [*] TrafficLight
TrafficLight [1] <---> [1] SignalState

Design Approach

Use the State pattern to prevent massive switch-case statements. Each state holds its display rules and references the next state in sequence.

Core Classes & Models

TrafficLight (Context class)SignalState (State interface)RedState, GreenState, YellowState (Concrete states)TrafficSignalController (Singleton orchestrating intersections)

Code Blueprint

public interface SignalState {
    void changeState(TrafficLight light);
    int getDuration();
}
public class RedState implements SignalState {
    public void changeState(TrafficLight l) { l.setState(new GreenState()); }
    public int getDuration() { return 30; }
}