package sale; import java.io.Serializable; import java.util.*; import users.User; /** * A node in the graph representing the deterministic finite automaton implementing a * {@link SaleProcess process}. * * <p>Gates are the points at which user communication and control flow branching take place. A process can * stay at a gate as long as may be necessary, but must be aware that it can be interrupted and * suspended at any time. In contrast, a process can never be interrupted when in a {@link Transition}, but * transitions must be very short and must not comprise any user communication.</p> * * <p>As every process begins and ends at a gate, there are special gates for special occasions. See * the <code>getXXXGate()</code> methods in {@link SaleProcess}.</p> * * @author Steffen Zschaler * @version 2.0 27/05/1999 * @since v2.0 */ public interface Gate extends Serializable { /** * Determine the next Transition. * * <p>This is the key (and sole) method of the gate. By entering this method, the calling process * enters the gate. This method must do anything that is necessary to determine the next transition * and must then return this transition. It is invalid, to return a <code>null</code> transition, * except in the special cases noted below.</p> * * <p>The method must be interruptible by calls to {@link java.lang.Thread#interrupt()} on the executing * thread and it must propagate these interrupts as a InterruptedException. In this case it is obviously no * problem, if the method returns a <code>null</code> transition.</p> * * <p>Also, if any other exception causes the method to be left, or in the case of an explicit call * to the process' {@link SaleProcess#error} method, the result may be <code>null</code>.</p> * * @override Always * * @param pOwner the process that entered the gate and triggered the method. * @param usr the user currently active in the process' {@link ProcessContext} * * @return the Transition to be performed after leaving the gate. * * @exception InterruptedException if an interrupt ocurred while at the gate. */ public Transition getNextTransition (SaleProcess pOwner, User usr) throws InterruptedException; }