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Questions and Answers
What does the State pattern make it appear as if an object has changed?
What is the main idea behind the concept of a Finite-State Machine?
What is the problem with a state machine based on conditionals?
What is the weakness of a state machine based on conditionals?
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What happens when you add more states and state-dependent behaviors to the Document class?
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What is the Document class an example of?
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What is the purpose of the State pattern?
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What is the impact of a lean state machine built with a limited set of conditionals on a project over time?
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Study Notes
State Behavioral Design Pattern
- The State pattern allows an object to change its behavior when its internal state changes, making it appear as if the object changed its class.
Finite-State Machine Concept
- A Finite-State Machine is a concept closely related to the State pattern.
- A program can be in one of a finite number of states at any given moment.
- Within each state, the program behaves differently, and can be switched to another state instantaneously.
- The program may or may not switch to certain other states depending on the current state.
- The switching rules, called transitions, are finite and predetermined.
State Machines in Object-Oriented Programming
- State machines can be applied to objects, allowing them to change behavior depending on their internal state.
- Example: a Document class can be in one of three states: Draft, Moderation, and Published.
- The publish method of the Document class behaves differently in each state.
Implementation of State Machines
- State machines are usually implemented using conditional statements (if or switch) that select the appropriate behavior depending on the current state.
- The "state" is often represented by a set of values of the object's fields.
Limitations of State Machines
- The biggest weakness of a state machine based on conditionals is that it becomes difficult to maintain as the number of states and state-dependent behaviors increases.
- Code becomes cluttered with monstrous conditionals, making it hard to predict and manage all possible states and transitions.
- Any change to the transition logic may require changing state conditionals in every method, making the code prone to errors and maintenance issues.
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Description
Learn about the State pattern and its relation to Finite-State Machines, changing behavior and internal state, and more.
