# Class SequencesComparator<T>

java.lang.Object
org.apache.commons.collections4.sequence.SequencesComparator<T>

Type Parameters:
  `T` - the type of elements in the lists.

public class SequencesComparator<T> extends Object
This class allows to compare two objects sequences.

The two sequences can hold any object type, as only the `equals` method is used to compare the elements of the sequences. It is guaranteed that the comparisons will always be done as `o1.equals(o2)` where `o1` belongs to the first sequence and `o2` belongs to the second sequence. This can be important if subclassing is used for some elements in the first sequence and the `equals` method is specialized.

Comparison can be seen from two points of view: either as giving the smallest modification allowing to transform the first sequence into the second one, or as giving the longest sequence which is a subsequence of both initial sequences. The `equals` method is used to compare objects, so any object can be put into sequences. Modifications include deleting, inserting or keeping one object, starting from the beginning of the first sequence.

This class implements the comparison algorithm, which is the very efficient algorithm from Eugene W. Myers An O(ND) Difference Algorithm and Its Variations. This algorithm produces the shortest possible `edit script` containing all the `commands` needed to transform the first sequence into the second one.

Since:
  4.0
See Also:
  - `EditScript`
  - `EditCommand`
  - `CommandVisitor`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `SequencesComparator(List<T> sequence1, List<T> sequence2)`
  Simple constructor.
  `SequencesComparator(List<T> sequence1, List<T> sequence2, Equator<? super T> equator)`
  Simple constructor.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `EditScript<T>`
  `getScript()`
  Gets the `EditScript` object.

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

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

- ## Constructor Details

  - ### SequencesComparator

    public SequencesComparator(List<T> sequence1, List<T> sequence2)
    Simple constructor.

    Creates a new instance of SequencesComparator using a `DefaultEquator`.

    It is guaranteed that the comparisons will always be done as `o1.equals(o2)` where `o1` belongs to the first sequence and `o2` belongs to the second sequence. This can be important if subclassing is used for some elements in the first sequence and the `equals` method is specialized.

    Parameters:
      `sequence1` - first sequence to be compared
      `sequence2` - second sequence to be compared

  - ### SequencesComparator

    public SequencesComparator(List<T> sequence1, List<T> sequence2, Equator<? super T> equator)
    Simple constructor.

    Creates a new instance of SequencesComparator with a custom `Equator`.

    It is guaranteed that the comparisons will always be done as `Equator.equate(o1, o2)` where `o1` belongs to the first sequence and `o2` belongs to the second sequence.

    Parameters:
      `sequence1` - first sequence to be compared
      `sequence2` - second sequence to be compared
      `equator` - the equator to use for testing object equality

- ## Method Details

  - ### getScript

    public EditScript<T> getScript()
    Gets the `EditScript` object.

    It is guaranteed that the objects embedded in the `insert commands` come from the second sequence and that the objects embedded in either the `delete commands` or `keep commands` come from the first sequence. This can be important if subclassing is used for some elements in the first sequence and the `equals` method is specialized.

    Returns:
      the edit script resulting from the comparison of the two sequences