Class HistoryList<T>
- java.lang.Object
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- util.HistoryList<T>
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- Type Parameters:
T
- the type of items in the list
public class HistoryList<T> extends java.lang.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 calladd(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.
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Constructor Summary
Constructors Constructor Description HistoryList(int size, java.util.function.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, java.util.function.Consumer<T> itemSelectedCallback)
The sized passed here limits the size of the list, with the oldest items being dropped as the list grows.
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Method Summary
All Methods Instance Methods Concrete Methods 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.java.util.List<T>
getNextHistoryItems()
Get all items in the history that come after the current history item.java.util.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 agoBack()
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 agoForward()
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 listjava.lang.String
toString()
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Constructor Detail
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HistoryList
public HistoryList(int size, java.util.function.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 whengoBack()
orgoForward()
are called.- Parameters:
size
- the max number of items to keep in the listitemSelectedCallback
- the function to call when the client selects an item by going back or forward
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HistoryList
public HistoryList(int size, java.util.function.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 whengoBack()
orgoForward()
are called.- Parameters:
size
- the max number of items to keep in the listitemSelectedCallback
- 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.
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Method Detail
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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
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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
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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.
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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.
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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.
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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.
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goBackTo
public void goBackTo(T t)
Performs agoBack()
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
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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.
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goForwardTo
public void goForwardTo(T t)
Performs agoForward()
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
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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.
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getPreviousHistoryItems
public java.util.List<T> getPreviousHistoryItems()
Get all items in the history that come before the current history item. They are returned in navigation order, as traversed ifgoBack()
is called.- Returns:
- the items
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getNextHistoryItems
public java.util.List<T> getNextHistoryItems()
Get all items in the history that come after the current history item. They are returned in navigation order, as traversed ifgoForward()
is called.- Returns:
- the items
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clear
public void clear()
Clears all history entries and resets the current item pointer.
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size
public int size()
Returns the number of items in this history list- Returns:
- the number of items in this history list
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toString
public java.lang.String toString()
- Overrides:
toString
in classjava.lang.Object
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