Neha Patil (Editor)

State pattern

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The state pattern is a behavioral software design pattern that implements a state machine in an object-oriented way. With the state pattern, a state machine is implemented by implementing each individual state as a derived class of the state pattern interface, and implementing state transitions by invoking methods defined by the pattern's superclass.

The state pattern can be interpreted as a strategy pattern which is able to switch the current strategy through invocations of methods defined in the pattern's interface.

This pattern is used in computer programming to encapsulate varying behavior for the same object based on its internal state. This can be a cleaner way for an object to change its behavior at runtime without resorting to large monolithic conditional statements and thus improve maintainability.

Java

The state interface and two implementations. The state’s method has a reference to the context object and is able to change its state.

The context class has a state variable that it instantiates in an initial state, in this case StateLowerCase. In its method, it uses the corresponding methods of the state object.

The demonstration below shows the usage:

With the above code, the output of main() from DemoOfClientState should be:

monday TUESDAY WEDNESDAY thursday FRIDAY SATURDAY sunday

References

State pattern Wikipedia


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