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Questions and Answers
What does the State pattern make it appear as if an object has changed?
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 main idea behind the concept of a Finite-State Machine?
What is the problem with a state machine based on conditionals?
What is the problem with a state machine based on conditionals?
What is the weakness of 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?
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?
What is the Document class an example of?
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What is the purpose of the State pattern?
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?
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.
