# Class ListChangeListener.Change<E>

java.lang.Object
javafx.collections.ListChangeListener.Change<E>

Type Parameters:
  `E` - the list element type

Enclosing interface:
  `ListChangeListener<E>`

public abstract static class ListChangeListener.Change<E> extends Object
Represents a report of changes done to an `ObservableList`. The change may consist of one or more actual changes and must be iterated by calling the `next()` method. Each change must be one of the following:

- Permutation change : `wasPermutated()` returns true in this case. The permutation happened at range between `from` (inclusive) and `to` (exclusive) and can be queried by calling `getPermutation(int)` method.
- Add or remove change : In this case, at least one of the `wasAdded()`, `wasRemoved()` returns true. If both methods return true, `wasReplaced()` will also return true.

  The `getRemoved()` method returns a list of elements that have been replaced or removed from the list.

  The range between `from` (inclusive) and `to` (exclusive) denotes the sublist of the list that contain new elements. Note that this is a half-open interval, so if no elements were added, `getFrom()` is equal to `getTo()`.

  It is possible to get a list of added elements by calling getAddedSubList().

  Note that in order to maintain correct indexes of the separate add/remove changes, these changes must be sorted by their `from` index.

- Update change : `wasUpdated()` return true on an update change. All elements between `from` (inclusive) and `to` (exclusive) were updated.

Important: It's necessary to call `next()` method before calling any other method of `Change`. The same applies after calling `reset()`. The only methods that works at any time is `getList()`.

Typical usage is to observe changes on an ObservableList in order to hook or unhook (or add or remove a listener) or in order to maintain some invariant on every element in that ObservableList. A common code pattern for doing this looks something like the following:

>      ObservableList<Item> theList = ...;

>      theList.addListener(new ListChangeListener<Item>() {
>          public void onChanged(Change<Item> c) {
>              while (c.next()) {
>                  if (c.wasPermutated()) {
>                      for (int i = c.getFrom(); i < c.getTo(); ++i) {
>                           //permutate
>                      }
>                  } else if (c.wasUpdated()) {
>                           //update item
>                  } else {
>                      for (Item remitem : c.getRemoved()) {
>                          remitem.remove(Outer.this);
>                      }
>                      for (Item additem : c.getAddedSubList()) {
>                          additem.add(Outer.this);
>                      }
>                  }
>              }
>          });

>      }

Warning: This class directly accesses the source list to acquire information about the changes.
This effectively makes the Change object invalid when another change occurs on the list.
For this reason it is not safe to use this class on a different thread.
It also means the source list cannot be modified inside the listener since that would invalidate this Change object for all subsequent listeners.

Note: in case the change contains multiple changes of different type, these changes must be in the following order: permutation change(s), add or remove changes, update changes This is because permutation changes cannot go after add/remove changes as they would change the position of added elements. And on the other hand, update changes must go after add/remove changes because they refer with their indexes to the current state of the list, which means with all add/remove changes applied.

Since:
  JavaFX 2.0

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `Change(ObservableList<E> list)`
  Constructs a new Change instance on the given list.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `int`
  `getAddedSize()`
  Returns the size of the interval that was added.
  `List<E>`
  `getAddedSubList()`
  Returns a subList view of the list that contains only the elements added.
  `abstract int`
  `getFrom()`
  If `wasAdded()` is true, the interval contains all the values that were added.
  `ObservableList<E>`
  `getList()`
  The source list of the change.
  `protected abstract int[]`
  `getPermutation()`
  If this change is a permutation, it returns an integer array that describes the permutation.
  `int`
  `getPermutation(int i)`
  This method allows developers to observe the permutations that occurred in this change.
  `abstract List<E>`
  `getRemoved()`
  An immutable list of removed/replaced elements.
  `int`
  `getRemovedSize()`
  Returns the size of `getRemoved()` list.
  `abstract int`
  `getTo()`
  The end of the change interval.
  `abstract boolean`
  `next()`
  Goes to the next change.
  `abstract void`
  `reset()`
  Resets to the initial stage.
  `boolean`
  `wasAdded()`
  Indicates if elements were added during this change.
  `boolean`
  `wasPermutated()`
  Indicates if the change was only a permutation.
  `boolean`
  `wasRemoved()`
  Indicates if elements were removed during this change.
  `boolean`
  `wasReplaced()`
  Indicates if elements were replaced during this change.
  `boolean`
  `wasUpdated()`
  Indicates that the elements between `getFrom()` (inclusive) to `getTo()` exclusive has changed.

  ### Methods declared in class java.lang.Object

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

- ## Constructor Details

  - ### Change

    public Change(ObservableList<E> list)
    Constructs a new Change instance on the given list.
    Parameters:
      `list` - The list that was changed

- ## Method Details

  - ### next

    public abstract boolean next()
    Goes to the next change. The Change instance, in its initial state, is invalid and requires a call to `next()` before calling other methods. The first `next()` call will make this object represent the first change.
    Returns:
      `true` if switched to the next change, `false` if this is the last change

  - ### reset

    public abstract void reset()
    Resets to the initial stage. After this call, `next()` must be called before working with the first change.

  - ### getList

    public ObservableList<E> getList()
    The source list of the change.
    Returns:
      a list that was changed

  - ### getFrom

    public abstract int getFrom()
    If `wasAdded()` is true, the interval contains all the values that were added. If `wasPermutated()` is true, the interval marks the values that were permutated. If `wasRemoved()` is true and `wasAdded` is false, `getFrom()` and `getTo()` should return the same number - the place where the removed elements were positioned in the list.
    Returns:
      a beginning (inclusive) of an interval related to the change
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### getTo

    public abstract int getTo()
    The end of the change interval.
    Returns:
      an end (exclusive) of an interval related to the change
    Throws:
      `IllegalStateException` - if this Change instance is in initial state
    See Also:
      - `getFrom()`

  - ### getRemoved

    public abstract List<E> getRemoved()
    An immutable list of removed/replaced elements. If no elements were removed from the list, an empty list is returned.
    Returns:
      a list with all the removed elements
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### wasPermutated

    public boolean wasPermutated()
    Indicates if the change was only a permutation.
    Returns:
      `true` if the change was just a permutation
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### wasAdded

    public boolean wasAdded()
    Indicates if elements were added during this change.
    Returns:
      `true` if something was added to the list
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### wasRemoved

    public boolean wasRemoved()
    Indicates if elements were removed during this change. Note that using set will also produce a change with `wasRemoved()` returning true. See `wasReplaced()`.
    Returns:
      `true` if something was removed from the list
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### wasReplaced

    public boolean wasReplaced()
    Indicates if elements were replaced during this change. This is usually true when set is called on the list. Set operation will act like remove and add operation at the same time.

    Usually, it's not necessary to use this method directly. Handling remove operation and then add operation, as in the example in the `ListChangeListener.Change` class javadoc, will effectively handle the set operation.

    Returns:
      same as `wasAdded() && wasRemoved()`
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### wasUpdated

    public boolean wasUpdated()
    Indicates that the elements between `getFrom()` (inclusive) to `getTo()` exclusive has changed. This is the only optional event type and may not be fired by all ObservableLists.
    Returns:
      `true` if the current change is an update change
    Since:
      JavaFX 2.1

  - ### getAddedSubList

    public List<E> getAddedSubList()
    Returns a subList view of the list that contains only the elements added. This is actually a shortcut to `c.getList().subList(c.getFrom(), c.getTo());`

         for (Node n : change.getAddedSubList()) {
               // do something
         }

    Returns:
      the newly created sublist view that contains all the added elements
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### getRemovedSize

    public int getRemovedSize()
    Returns the size of `getRemoved()` list.
    Returns:
      the number of removed items
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### getAddedSize

    public int getAddedSize()
    Returns the size of the interval that was added.
    Returns:
      the number of added items
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### getPermutation

    protected abstract int[] getPermutation()
    If this change is a permutation, it returns an integer array that describes the permutation. This array maps directly from the previous indexes to the new ones. This method is not publicly accessible and therefore can return an array safely. The 0 index of the array corresponds to index `getFrom()` of the list. The same applies for the last index and `getTo()`. The method is used by `wasPermutated()` and `getPermutation(int)` methods.
    Returns:
      empty array if this is not permutation or an integer array containing the permutation
    Throws:
      `IllegalStateException` - if this Change instance is in initial state

  - ### getPermutation

    public int getPermutation(int i)
    This method allows developers to observe the permutations that occurred in this change. In order to get the new position of an element, you must call:

            change.getPermutation(oldIndex);

    Note: default implementation of this method takes the information from `getPermutation()` method. You don't have to override this method.
    Parameters:
      `i` - the old index that contained the element prior to this change
    Returns:
      the new index of the same element
    Throws:
      `IndexOutOfBoundsException` - if i is out of the bounds of the list
      `IllegalStateException` - if this is not a permutation change