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



return true;

    }, ROOT {

  public boolean process(Context context) {

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

// read root tag



return true;

public void process(Context context) {

Related Article:

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

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.
Notify of

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

Inline Feedbacks
View all comments
Back to top button