Package util

Class HistoryList<T>

java.lang.Object

util.HistoryList<T>

Type Parameters:

T - the type of items in the list

public class HistoryList<T>
extends Object

An object meant to track items with the ability to go back and forth within the list of items.

By default, duplicate entries are not allowed. This allows for a simplified history of unique items. If the client prefers to have an accurate history, then call setAllowDuplicates(boolean) in order to keep all history entries.

By default, null values are not allowed. If the client allows null/empty values, then they should call setAllowNulls(boolean) with a value of true. This allows the backward navigation to work correctly when the client's active item is cleared. When that item is cleared, then client is expected to call add(Object) with value of null. (This is safe to do, regardless of whether null are allowed). When nulls are allowed and a null value is received, then current item is placed onto the history stack as the previous item. This way, when the user presses the back button, the last visible item will be activated.

Note: when nulls are allowed, only a single null value will be stored. Further, if new, non-null items are added, then the null value is dropped.

Constructor Summary

Constructors

Constructor	Description
HistoryList(int size, BiConsumer<T,T> itemSelectedCallback)	The sized passed here limits the size of the list, with the oldest items being dropped as the list grows.
HistoryList(int size, Consumer<T> itemSelectedCallback)	The sized passed here limits the size of the list, with the oldest items being dropped as the list grows.

Method Summary

Modifier and Type	Method	Description
void	add(T t)	Adds an item to this history list.
void	clear()	Clears all history entries and resets the current item pointer.
T	getCurrentHistoryItem()	Returns the item currently pointed to within the list of items.
List<T>	getNextHistoryItems()	Get all items in the history that come after the current history item.
List<T>	getPreviousHistoryItems()	Get all items in the history that come before the current history item.
void	goBack()	Moves this history list's current item pointer back one and then calls the user-provided callback to signal the newly selected item.
void	goBackTo(T t)	Performs a goBack() until the given item becomes the current item.
void	goForward()	Moves this history list's current item pointer forward one and then calls the user-provided callback to signal the newly selected item.
void	goForwardTo(T t)	Performs a goForward() until the given item becomes the current item.
boolean	hasNext()	Returns true if this history list's current item pointer is not at the end of the list.
boolean	hasPrevious()	Returns true if this history list's current item pointer is not at the beginning of the list.
void	setAllowDuplicates(boolean allowDuplicates)	True signals that this list will allow duplicate entries.
void	setAllowNulls(boolean allowNulls)	True signals that the client allows null items to be used.
int	size()	Returns the number of items in this history list
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Details

HistoryList

public HistoryList(int size,
 Consumer<T> itemSelectedCallback)

The sized passed here limits the size of the list, with the oldest items being dropped as the list grows. The given callback will be called when goBack() or goForward() are called.

Parameters:

size - the max number of items to keep in the list

itemSelectedCallback - the function to call when the client selects an item by going back or forward

HistoryList

public HistoryList(int size,
 BiConsumer<T,T> itemSelectedCallback)

The sized passed here limits the size of the list, with the oldest items being dropped as the list grows. The given callback will be called when goBack() or goForward() are called.

Parameters:

size - the max number of items to keep in the list

itemSelectedCallback - the function to call when the client selects an item by going back or forward. This callback will be passed the newly selected item as the first argument and the previously selected item as the second argument.

Method Details

setAllowDuplicates

public void setAllowDuplicates(boolean allowDuplicates)

True signals that this list will allow duplicate entries. False signals to not only not allow duplicates, but to also move the position of an item if it is re-added to the list.

For correct behavior when not allowing duplicates, ensure you have defined an equals method to work as you expect. If two different items are considered equal, then this class will only remove the duplicate if the equals method returns true.

The default is false

Parameters:

allowDuplicates - true to allow duplicates

setAllowNulls

public void setAllowNulls(boolean allowNulls)

True signals that the client allows null items to be used. When this is true, a null value will be stored in this list only as the last item. See the javadoc for more info.

Parameters:

allowNulls - true to allow nulls; the default is false

add

public void add(T t)

Adds an item to this history list. null values are ignored.

Calls to this method during selection notification will have no effect. If you need to update the history during a notification, then you must do so at a later time, perhaps by using SystemUtilities.runSwingLater(Runnable).

Parameters:

t - the item to add.

hasNext

public boolean hasNext()

Returns true if this history list's current item pointer is not at the end of the list.

Returns:

true if this history list's current item pointer is not at the end of the list.

hasPrevious

public boolean hasPrevious()

Returns true if this history list's current item pointer is not at the beginning of the list.

Returns:

true if this history list's current item pointer is not at the beginning of the list.

goBack

public void goBack()

Moves this history list's current item pointer back one and then calls the user-provided callback to signal the newly selected item.

No action is taken if the current pointer is already at the beginning of the list.

goBackTo

public void goBackTo(T t)

Performs a goBack() until the given item becomes the current item. This is useful if you wish to go backward to a specific item in the list.

Parameters:

t - the item

goForward

public void goForward()

Moves this history list's current item pointer forward one and then calls the user-provided callback to signal the newly selected item.

No action is taken if the current pointer is already at the end of the list.

goForwardTo

public void goForwardTo(T t)

Performs a goForward() until the given item becomes the current item. This is useful if you wish to go forward to a specific item in the list.

Parameters:

t - the item

getCurrentHistoryItem

public T getCurrentHistoryItem()

Returns the item currently pointed to within the list of items. When an item is added, this will be that item. Otherwise, it will be the last item navigated.

Returns:

the item currently pointed to within the list of items.

getPreviousHistoryItems

public List<T> getPreviousHistoryItems()

Get all items in the history that come before the current history item. They are returned in navigation order, as traversed if goBack() is called.

Returns:

the items

getNextHistoryItems

public List<T> getNextHistoryItems()

Get all items in the history that come after the current history item. They are returned in navigation order, as traversed if goForward() is called.

Returns:

the items

clear

public void clear()

Clears all history entries and resets the current item pointer.

size

public int size()

Returns the number of items in this history list

Returns:

the number of items in this history list

toString

public String toString()

Overrides:

toString in class Object