Home » Java Basics » data types » Enum » Using an enum as a state machine

About Byron Kiourtzoglou

Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Using an enum as a state machine

In this short example, a parser state machine processes raw XML from a ByteBuffer. Each state has its own process method and if there is not enough data available, the state machine can return to retrieve more data. Each transition between states is well defined and the code for all states is together in one enum.

interface Context {
    ByteBuffer buffer();
    State state();
    void state(State state);
}
interface State {
    /**

 * @return true to keep processing, false to read more data.
     */
    boolean process(Context context);
}
enum States implements State {
    XML {

  public boolean process(Context context) {


if (context.buffer().remaining() < 16) return false;


// read header


if(headerComplete)


    context.state(States.ROOT);


return true;

  }
    }, ROOT {

  public boolean process(Context context) {


if (context.buffer().remaining() < 8) return false;


// read root tag


if(rootComplete)


    context.state(States.IN_ROOT);


return true;

  }
    }
}
 
public void process(Context context) {
    socket.read(context.buffer());
    while(context.state().process(context));
}

Related Article:

Reference: Java Secret: Using an enum to build a State machine from our JCG partner Peter Lawrey at the Vanilla Java

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments