The Wikipedia article for State Pattern has a Java example that illustrates two states, involving two different methods. Those methods can be arbitrarily complex, so I consider a two-state solution (no pun intended) perfectly valid.
interface Statelike {
void writeName(StateContext context, String name);
}
class StateLowerCase implements Statelike {
@Override
public void writeName(final StateContext context, final String name) {
System.out.println(name.toLowerCase());
context.setState(new StateMultipleUpperCase());
}
}
class StateMultipleUpperCase implements Statelike {
/** Counter local to this state */
private int count = 0;
@Override
public void writeName(final StateContext context, final String name) {
System.out.println(name.toUpperCase());
/* Change state after StateMultipleUpperCase's writeName() gets invoked twice */
if(++count > 1) {
context.setState(new StateLowerCase());
}
}
}
Note that writeName swaps out its own implementation by handing a new StateLike object to the StateContext when the i count exceeds one.
class StateContext {
private Statelike myState;
StateContext() {
setState(new StateLowerCase());
}
/**
* Setter method for the state.
* Normally only called by classes implementing the State interface.
* @param newState the new state of this context
*/
void setState(final Statelike newState) {
myState = newState;
}
public void writeName(final String name) {
myState.writeName(this, name);
}
}
A State Pattern would be indicated if your "machinery" substantially changes between states. The complexity of the condition needed to choose the correct processing object doesn't matter; it's the complexity of the state objects themselves that are the deciding factor. Otherwise, you could just write all of the logic into a single class.
Think about what happens when you build a car. The chassis moves along an assembly line and stops at a station where the welding takes place. Once that state has completed, the chassis moves to the next station on the assembly line, where a different set of robots with completely different programming installs the engine.
