chargerlib.undo

Class UndoRedoList<T>

Object

chargerlib.undo.UndoRedoList<T>

public class UndoRedoList<T>
extends Object

Implements the undo and redo logic. Relies only on there being some UndoableState subclass as the state being stored. Operates as follows: Consider a list of sequential states numbered 0, 1, ... , maxUndo-1 from past to future. There is a position currentIndex that is the current state. There are three operations of interest:

• Do something that's undoable -- increment currentIndex, save that something, and nullify remainder of list.
• Undo - decrement currentIndex, then return content at currentIndex. This leaves the redo state still on the list (at currentIndex + 1), to be re-done if required.
• Redo - increment currentIndex, return content from there.

Since:

Charger 3.8.3

Field Summary

Fields

Modifier and Type	Field and Description
protected int	currentIndex the index into the state list telling us which state is the current one.
int	maxUndo Maximum number of states that are undo-able -- currently set to 10
protected ArrayList<T>	stateList Each past copy of the graph, in text form, is added to the list, up to its max

Constructor Summary

Constructors

Constructor and Description
UndoRedoList() Create an empty undo/redo structure
UndoRedoList(int max) Allows user to decide how many undo steps are saved.

Method Summary

Modifier and Type	Method and Description
T	mostRecentState() Get the state on the top of the stack, but do not pop it! Does not alter the undo/redo list.
T	popRedo() Restore a previous state, moving forward with respect to the saved states.
T	popUndo() Undo the last editing newState.
void	pushCurrent(T currentState) Track a regular editing action (other than undo or redo) by pushing it onto the undo list.
boolean	redoAvailable()
void	reset() Initialize the undo/redo sequences, so that there are no past or future states.
String	toString() Generally used for debugging
boolean	undoAvailable()

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

maxUndo

public int maxUndo

Maximum number of states that are undo-able -- currently set to 10

stateList

protected ArrayList<T> stateList

Each past copy of the graph, in text form, is added to the list, up to its max

currentIndex

protected int currentIndex

the index into the state list telling us which state is the current one. If -1 then there is no current state.

Constructor Detail

UndoRedoList

public UndoRedoList()

Create an empty undo/redo structure

UndoRedoList

public UndoRedoList(int max)

Allows user to decide how many undo steps are saved. Also applies to redo. If the max is reached, all states are "scooted" down one, losing the oldest state, and the most recent one is placed at the end.

Method Detail

undoAvailable

public boolean undoAvailable()

Returns:

whether there is a previous newState which we can restore.

See Also:

popUndo()

redoAvailable

public boolean redoAvailable()

Returns:

whether there is a next newState which can be re-done.

See Also:

popRedo()

popUndo

public T popUndo()

Undo the last editing newState. Pushes a current state onto the redo stack and pops the last copy of the state from the undoStack, to become the current editing newState. restored via "redo". Implementer must explicitly use the returned state to set the current state.

Returns:

The previous state to be be restored.

popRedo

public T popRedo()

Restore a previous state, moving forward with respect to the saved states. Pushes the most recent state onto the undo stack and pops the next "future" state from the redo stack. Implementer must explicitly use the returned state to set the current state.

Returns:

The next ("future") editing action.

pushCurrent

public void pushCurrent(T currentState)

Track a regular editing action (other than undo or redo) by pushing it onto the undo list. Wipes out any "redo" chain of events -- after this, all the previously saved future states are gone. In science fiction terms, we have thus altered the future timeline and no previous future timelines can occur.

Parameters:

currentState - The most recent editing action. If null, then there's no change.

reset

public void reset()

Initialize the undo/redo sequences, so that there are no past or future states. Populates the state list with null values so it will be the right size. Sets the current index to -1

toString

public String toString()

Generally used for debugging

Overrides:

toString in class Object

mostRecentState

public T mostRecentState()

Get the state on the top of the stack, but do not pop it! Does not alter the undo/redo list.

Returns:

the state on top of the stack (most recent one); if there isn't one, then return null.