Package org.eclipse.jetty.util

Class TopologicalSort<T>

java.lang.Object
org.eclipse.jetty.util.TopologicalSort<T>
Type Parameters:
T - The type to be sorted. It must be able to be added to a HashSet
public class TopologicalSort<T> extends Object
Topological sort a list or array.

A Topological sort is used when you have a partial ordering expressed as dependencies between elements (also often represented as edges in a directed acyclic graph). A Topological sort should not be used when you have a total ordering expressed as a Comparator over the items. The algorithm has the additional characteristic that dependency sets are sorted by the original list order so that order is preserved when possible.

The sort algorithm works by recursively visiting every item, once and only once. On each visit, the items dependencies are first visited and then the item is added to the sorted list. Thus the algorithm ensures that dependency items are always added before dependent items.

  • Constructor Details

    • TopologicalSort

      public TopologicalSort()

  • Method Details

    • addDependency

      public void addDependency(T dependent, T... dependency)
      Add a dependency to be considered in the sort.
      Parameters:
      dependent - The dependent item will be sorted after all its dependencies
      dependency - The dependency item, will be sorted before its dependent item

    • addBeforeAfter

      public void addBeforeAfter(T before, T after)
      An alternative to addDependency(Object, Object[]), which is equivalent to addDependency(after,before) as the after item is dependent of the before item.
      Parameters:
      before - The item will be sorted before the after
      after - The item will be sorted after the before

    • sort

      public void sort(T[] array)
      Sort the passed array according to dependencies previously set with addDependency(Object, Object[]). Where possible, ordering will be preserved if no dependency
      Parameters:
      array - The array to be sorted.

    • sort

      public void sort(Collection<T> list)
      Sort the passed list according to dependencies previously set with addDependency(Object, Object[]). Where possible, ordering will be preserved if no dependency
      Parameters:
      list - The list to be sorted.

    • toString

      public String toString()
      Overrides:
      toString in class Object