Class StringsComparator
- java.lang.Object
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- org.apache.commons.text.diff.StringsComparator
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public class StringsComparator extends java.lang.Object
It is guaranteed that the comparisons will always be done as
o1.equals(o2)
whereo1
belongs to the first sequence ando2
belongs to the second sequence. This can be important if subclassing is used for some elements in the first sequence and theequals
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 thecommands
needed to transform the first sequence into the second one.This code has been adapted from Apache Commons Collections 4.0.
- Since:
- 1.0
- See Also:
EditScript
,EditCommand
,CommandVisitor
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Nested Class Summary
Nested Classes Modifier and Type Class Description private static class
StringsComparator.Snake
This class is a simple placeholder to hold the end part of a path under construction in aStringsComparator
.
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Constructor Summary
Constructors Constructor Description StringsComparator(java.lang.String left, java.lang.String right)
Constructs a new instance of StringsComparator.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description private void
buildScript(int start1, int end1, int start2, int end2, EditScript<java.lang.Character> script)
Builds an edit script.private StringsComparator.Snake
buildSnake(int start, int diag, int end1, int end2)
Builds a snake.private StringsComparator.Snake
getMiddleSnake(int start1, int end1, int start2, int end2)
Gets the middle snake corresponding to two subsequences of the main sequences.EditScript<java.lang.Character>
getScript()
Gets theEditScript
object.
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Constructor Detail
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StringsComparator
public StringsComparator(java.lang.String left, java.lang.String right)
Constructs a new instance of StringsComparator.It is guaranteed that the comparisons will always be done as
o1.equals(o2)
whereo1
belongs to the first sequence ando2
belongs to the second sequence. This can be important if subclassing is used for some elements in the first sequence and theequals
method is specialized.- Parameters:
left
- first character sequence to be comparedright
- second character sequence to be compared
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Method Detail
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buildScript
private void buildScript(int start1, int end1, int start2, int end2, EditScript<java.lang.Character> script)
Builds an edit script.- Parameters:
start1
- the begin of the first sequence to be comparedend1
- the end of the first sequence to be comparedstart2
- the begin of the second sequence to be comparedend2
- the end of the second sequence to be comparedscript
- the edited script
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buildSnake
private StringsComparator.Snake buildSnake(int start, int diag, int end1, int end2)
Builds a snake.- Parameters:
start
- the value of the start of the snakediag
- the value of the diagonal of the snakeend1
- the value of the end of the first sequence to be comparedend2
- the value of the end of the second sequence to be compared- Returns:
- The snake built
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getMiddleSnake
private StringsComparator.Snake getMiddleSnake(int start1, int end1, int start2, int end2)
Gets the middle snake corresponding to two subsequences of the main sequences.The snake is found using the MYERS Algorithm (this algorithms has also been implemented in the GNU diff program). This algorithm is explained in Eugene Myers article: An O(ND) Difference Algorithm and Its Variations.
- Parameters:
start1
- the begin of the first sequence to be comparedend1
- the end of the first sequence to be comparedstart2
- the begin of the second sequence to be comparedend2
- the end of the second sequence to be compared- Returns:
- The middle snake
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getScript
public EditScript<java.lang.Character> getScript()
Gets theEditScript
object.It is guaranteed that the objects embedded in the
insert commands
come from the second sequence and that the objects embedded in either thedelete commands
orkeep commands
come from the first sequence. This can be important if subclassing is used for some elements in the first sequence and theequals
method is specialized.- Returns:
- The edit script resulting from the comparison of the two sequences
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