org.apache.commons.collections4.comparators

## Class ComparatorChain<E>

- java.lang.Object
- - org.apache.commons.collections4.comparators.ComparatorChain<E>

- All Implemented Interfaces:
    Serializable, Comparator<E>

      public class ComparatorChain<E>
      extends Object
      implements Comparator<E>, Serializable

  A ComparatorChain is a Comparator that wraps one or more Comparators in sequence. The ComparatorChain calls each Comparator in sequence until either 1) any single Comparator returns a non-zero result (and that result is then returned), or 2) the ComparatorChain is exhausted (and zero is returned). This type of sorting is very similar to multi-column sorting in SQL, and this class allows Java classes to emulate that kind of behaviour when sorting a List.

  To further facilitate SQL-like sorting, the order of any single Comparator in the list can be reversed.

  Calling a method that adds new Comparators or changes the ascend/descend sort after compare(Object, Object) has been called will result in an UnsupportedOperationException. However, take care to not alter the underlying List of Comparators or the BitSet that defines the sort order.

  Instances of ComparatorChain are not synchronized. The class is not thread-safe at construction time, but it is thread-safe to perform multiple comparisons after all the setup operations are complete.

  Since:
    2.0
  Version:
    $Id: ComparatorChain.java 1533984 2013-10-20 21:12:51Z tn $
  See Also:
    Serialized Form

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `ComparatorChain()` Construct a ComparatorChain with no Comparators.
    `ComparatorChain(Comparator<E> comparator)` Construct a ComparatorChain with a single Comparator, sorting in the forward order
    `ComparatorChain(Comparator<E> comparator, boolean reverse)` Construct a Comparator chain with a single Comparator, sorting in the given order
    `ComparatorChain(List<Comparator<E>> list)` Construct a ComparatorChain from the Comparators in the List.
    `ComparatorChain(List<Comparator<E>> list, BitSet bits)` Construct a ComparatorChain from the Comparators in the given List.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addComparator(Comparator<E> comparator)` Add a Comparator to the end of the chain using the forward sort order
    `void` | `addComparator(Comparator<E> comparator, boolean reverse)` Add a Comparator to the end of the chain using the given sort order
    `int` | `compare(E o1, E o2)` Perform comparisons on the Objects as per Comparator.compare(o1,o2).
    `boolean` | `equals(Object object)` Returns `true` iff that Object is is a `Comparator` whose ordering is known to be equivalent to mine.
    `int` | `hashCode()` Implement a hash code for this comparator that is consistent with `equals`.
    `boolean` | `isLocked()` Determine if modifications can still be made to the ComparatorChain.
    `void` | `setComparator(int index, Comparator<E> comparator)` Replace the Comparator at the given index, maintaining the existing sort order.
    `void` | `setComparator(int index, Comparator<E> comparator, boolean reverse)` Replace the Comparator at the given index in the ComparatorChain, using the given sort order
    `void` | `setForwardSort(int index)` Change the sort order at the given index in the ComparatorChain to a forward sort.
    `void` | `setReverseSort(int index)` Change the sort order at the given index in the ComparatorChain to a reverse sort.
    `int` | `size()` Number of Comparators in the current ComparatorChain.

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### ComparatorChain

          public ComparatorChain()

      Construct a ComparatorChain with no Comparators. You must add at least one Comparator before calling the compare(Object,Object) method, or an UnsupportedOperationException is thrown

    - #### ComparatorChain

          public ComparatorChain(Comparator<E> comparator)

      Construct a ComparatorChain with a single Comparator, sorting in the forward order
      Parameters:
        `comparator` - First comparator in the Comparator chain

    - #### ComparatorChain

          public ComparatorChain(Comparator<E> comparator,
                         boolean reverse)

      Construct a Comparator chain with a single Comparator, sorting in the given order
      Parameters:
        `comparator` - First Comparator in the ComparatorChain
        `reverse` - false = forward sort; true = reverse sort

    - #### ComparatorChain

          public ComparatorChain(List<Comparator<E>> list)

      Construct a ComparatorChain from the Comparators in the List. All Comparators will default to the forward sort order.
      Parameters:
        `list` - List of Comparators
      See Also:
        `ComparatorChain(List,BitSet)`

    - #### ComparatorChain

          public ComparatorChain(List<Comparator<E>> list,
                         BitSet bits)

      Construct a ComparatorChain from the Comparators in the given List. The sort order of each column will be drawn from the given BitSet. When determining the sort order for Comparator at index i in the List, the ComparatorChain will call BitSet.get(i). If that method returns false, the forward sort order is used; a return value of true indicates reverse sort order.
      Parameters:
        `list` - List of Comparators. NOTE: This constructor does not perform a defensive copy of the list
        `bits` - Sort order for each Comparator. Extra bits are ignored, unless extra Comparators are added by another method.

  - ### Method Detail

    - #### addComparator

          public void addComparator(Comparator<E> comparator)

      Add a Comparator to the end of the chain using the forward sort order
      Parameters:
        `comparator` - Comparator with the forward sort order

    - #### addComparator

          public void addComparator(Comparator<E> comparator,
                           boolean reverse)

      Add a Comparator to the end of the chain using the given sort order
      Parameters:
        `comparator` - Comparator to add to the end of the chain
        `reverse` - false = forward sort order; true = reverse sort order

    - #### setComparator

          public void setComparator(int index,
                           Comparator<E> comparator)
                             throws IndexOutOfBoundsException

      Replace the Comparator at the given index, maintaining the existing sort order.
      Parameters:
        `index` - index of the Comparator to replace
        `comparator` - Comparator to place at the given index
      Throws:
        `IndexOutOfBoundsException` - if index < 0 or index >= size()

    - #### setComparator

          public void setComparator(int index,
                           Comparator<E> comparator,
                           boolean reverse)

      Replace the Comparator at the given index in the ComparatorChain, using the given sort order
      Parameters:
        `index` - index of the Comparator to replace
        `comparator` - Comparator to set
        `reverse` - false = forward sort order; true = reverse sort order

    - #### setForwardSort

          public void setForwardSort(int index)

      Change the sort order at the given index in the ComparatorChain to a forward sort.
      Parameters:
        `index` - Index of the ComparatorChain

    - #### setReverseSort

          public void setReverseSort(int index)

      Change the sort order at the given index in the ComparatorChain to a reverse sort.
      Parameters:
        `index` - Index of the ComparatorChain

    - #### size

          public int size()

      Number of Comparators in the current ComparatorChain.
      Returns:
        Comparator count

    - #### isLocked

          public boolean isLocked()

      Determine if modifications can still be made to the ComparatorChain. ComparatorChains cannot be modified once they have performed a comparison.
      Returns:
        true = ComparatorChain cannot be modified; false = ComparatorChain can still be modified.

    - #### compare

          public int compare(E o1,
                    E o2)
                      throws UnsupportedOperationException

      Perform comparisons on the Objects as per Comparator.compare(o1,o2).
      Specified by:
        `compare` in interface `Comparator<E>`
      Parameters:
        `o1` - the first object to compare
        `o2` - the second object to compare
      Returns:
        -1, 0, or 1
      Throws:
        `UnsupportedOperationException` - if the ComparatorChain does not contain at least one Comparator

    - #### hashCode

          public int hashCode()

      Implement a hash code for this comparator that is consistent with `equals`.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        a suitable hash code
      Since:
        3.0

    - #### equals

          public boolean equals(Object object)

      Returns `true` iff that Object is is a `Comparator` whose ordering is known to be equivalent to mine.

      This implementation returns `true` iff `object.`getClass()`` equals `this.getClass()`, and the underlying comparators and order bits are equal. Subclasses may want to override this behavior to remain consistent with the `Comparator.equals(Object)` contract.

      Specified by:
        `equals` in interface `Comparator<E>`
      Overrides:
        `equals` in class `Object`
      Parameters:
        `object` - the object to compare with
      Returns:
        true if equal
      Since:
        3.0

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