echopointng.history
Interface HistoryState

All Superinterfaces:

java.io.Serializable

All Known Subinterfaces:

HistoryUndoRedo

public interface HistoryState

extends java.io.Serializable

HistoryState is a interface that represents an application state at a given point of time.

The objects that implement this interface will typically contain state information that allows an application to go backwards (ie undo some actions) and go forwards (ie redo some actions).

See Also:

HistoryMonitor, HistoryEvent, HistoryEventListener

Method Summary

java.lang.String

historyHash() This is a unique history hash value that can be used to uniquely identify this particular slice of application state.

Method Detail

historyHash

public java.lang.String historyHash()

This is a unique history hash value that can be used to uniquely identify this particular slice of application state. This method should follow the same semantics as Object.hashCode() especially in regards to how it acts when used as the key of a java.util.Map.

The value used be will be display to the user on their browser as indication of where they are inside the application. Therefore there are some size contrictions on the length of this string which is the maximum size of a URL parameter in the users browser. To be safe use fairly compact strings (< 256 chars say)

This is method is defined as a String to allow more meaningful state to be displayed and also to allow possible "encoding" of application state in the hashCode itself.

The most trivial implementation fo this method would be

    public String historyHash() {
       return String.valueOf(this.hashCode());
    }
 

A more human friendly implementation might be something like this

 public String historyHash() {
    return whatAreWeDoing + "-" + System.identityHashCode(new Object());
 }
 

Returns:

- a unique history hash code