shadyy10 / JavaPatterns_State

Software design patterns - State (Java)

Java Patterns | State

State is a behavioral design pattern that allows an object to change its behavior depending on its inner state.

It is closely related to the finite state machine (FSM) concept.

• Online resource: State Pattern (refactoring guru)

Aplication

This repository implements a MusicPlayer that provides the following commands (public methods):

• ⏯️ play()
• ⏪ prev()
• ⏩ next()
• ⏹️ stop()
• ❓ status()

Its behavior for each command is defined through usage of the State pattern (see code) and "implements" the following FSM:

---

The program provided in the Main class gives us a command-line interface to interact with a MusicPlayer instance.

Run the program and check that, indeed, it behaves accordingly to the diagram above.

Exercises

1. Create a new concrete state in the class PausedState and change the existing ones to achieve the following FSM:

   

   💡 There is no need to make changes to the CLI class.

2. Add turnOn() and turnOff() methods to MusicPlayer. The behavior of these methods should be delegated to the current state. Note that this requires changing the MusicPlayerState interface. Create a new OffState and make the necessary changes to implement the following FSM:

   

   • ⚠️ Please note:

     • The previous transition rules between existing states stay the same; they are ommited from the above diagram;

     • The initial state is the Off;

     • You can only transition from the Off with the TURNON command; all others are silently ignored.

     • All other states silently ignore the TURNON command.

     • When transitioning from Off state to Stopped state the player must always load the first song of the playlist;

     • Whenever a transition is made to Stopped state the playback must stop and resources freed.

Solutions are provided here.