State Design Pattern Tutorial with Java Code Example for Beginners

State design pattern is a type of behavioral design pattern. State is a behavioral design pattern that lets an object alter its behavior when its internal state changes. It appears as if the object changed its class. This pattern provides a cleaner way for an object to change its type at runtime. We can achieve this using dynamic inheritance along with composition, where different subclasses represent different states and functionality and an object can switch its type during the runtime.

The State pattern is used when you want to have an enclosing class switch between a number of related contained classes, and pass method calls on to the current contained class.

Many programmers creating a class which performs slightly different functionality based on the arguments passed into the class. This frequently leads to a switch-case or if-else statements inside the class that determine which behavior to carry out. This becomes inelegance and dirty. State pattern solves this problem in a cleaner way. State pattern allows an object to change its behavior depending on the current values of the object.

The State pattern suggests that you create new classes for all possible states of an object and extract all state-specific behaviors into these classes. Instead of implementing all behaviors in original object, save a reference to one of the state objects in original object. State object represents the current state of original object, and delegates all the state-related work to this state object.

In original object, to change the state to another state, replace the state object with another state object i.e., draft to moderation. So here object is changing it behaviour as an embedded state object has changed. But remember that this possible only if all state classes are derived from a common interface.

** Where to use State Design Pattern **
1. Use the State pattern when you have an object that behaves differently depending on its current state, the number of states is enormous, and the state-specific code changes frequently.
2. The pattern suggests that you extract all state-specific code into a set of distinct classes. As a result, you can add new states or change existing ones independently of each other, reducing the maintenance cost.

** Advantages of State Design Pattern **
1. Single Responsibility Principle. Organize the code related to particular states into separate classes.
2. Open/Closed Principle. Introduce new states without changing existing state classes or the context.


** Chapter Timestamps **
0:00 Welcome to State Design Pattern
0:24 Recap of Command Design Pattern
1:28 Introduction of State Design Pattern
2:59 Example of State Design Pattern
5:36 Java code example of State Design Pattern
9:38 Usage of State Design Pattern
10:34 Advantages of State Design Pattern
11:09 Summary of State Design Pattern
11:46 Next video on Strategy Design Pattern

#statepattern #statedesignpattern #javadesignpatterns

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** Acronyms **
OOP – Object Oriented Programming Languages
GOF – Gang of Four Design Pattern
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