Java state mode, linux learning experience

The state pattern

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Use scenarios

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In this case, we demonstrate through the check-in of the hotel , There are several states of hotel rooms : Booked , I have checked in , Free . If we don't use state mode, our implementation is as follows :

if(state==“ Free ”){

if( Make a room reservation ){

Scheduled operation ;

state=“ Booked ”;

}else if( Live in a room ){

Check in operation ;

state=“ I have checked in ”;

}

}else if

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(“ Booked "){

if( Live in a room ){

Check in operation ;

state=“ I have checked in ”;

}else if( Cancel the reservation ){

Cancel operation ;

state=“ Free ”;

}

}

In this realization if Too many sentences , Inconvenient for maintenance and modification . At this time, we can consider using state mode to realize .

State mode implementation

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The class diagram structure

The core ：

It is used to solve the state transformation of complex objects in the system and the encapsulation of behaviors in different states

| role | explain |

| — | :-- |

| Context The environment class | Maintain one in the environment class State object , He defines the current state . |

| State | Specific status class |

| ConcreteState Specific status class | Each class encapsulates the behavior corresponding to a state |

Implementation code

State

/**

• State Interface

• @author Bobo roast duck

• @email [email protected]

*/

public interface State {

void handle();

}

State Implementation class

/**

• Booked status

• @author Bobo roast duck

• @email [email protected]

*/

public class BookedState implements State {

@Override

public void handle() {

System.out.println(“ The room is reserved ！ No one else can decide ！”);

}

}

/**

• Occupancy status

• @author Bobo roast duck

• @email [email protected]

*/

public class CheckedInState implements State {

@Override

public void handle() {

System.out.println(“ The room has been checked in ！ Do not disturb. ！”);

}

}

/**

• Idle state

• @author Bobo roast duck

• @email [email protected]

*/

public class FreeState implements State {

@Override

public void handle() {

System.out.println(“ The room is free ！！！ No one lives ！”);

}

}

Room object

/**

• Room object

• @author Bobo roast duck

• @email [email protected]

*/

public class HomeContext {

// If it's the banking system , This Context Class is account number . Depending on the amount , Switch between different states ！