Package org.apache.commons.collections4.comparators

Class ComparatorChain<E>

java.lang.Object
org.apache.commons.collections4.comparators.ComparatorChain<E>
Type Parameters:
E - the type of objects compared by this comparator
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 behavior 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
See Also:

  • Constructor Details

    • ComparatorChain

      public ComparatorChain()
      Constructs 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)
      Constructs 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)
      Constructs 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)
      Constructs 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

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

    • 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

    • 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

    • equals

      public boolean equals(Object object)
      Returns true iff that Object is a Comparator whose ordering is known to be equivalent to mine.

      This implementation returns true iff <i>object</i>.{@link Object#getClass() 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

    • 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

    • 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.

    • 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