org.apache.commons.io.comparator

## Class ExtensionFileComparator

- java.lang.Object
- - org.apache.commons.io.comparator.ExtensionFileComparator

- All Implemented Interfaces:
    Serializable, Comparator<File>

      public class ExtensionFileComparator
      extends Object
      implements Serializable

  Compare the file name extensions for order (see `FilenameUtils.getExtension(String)`).

  This comparator can be used to sort lists or arrays of files by their file extension either in a case-sensitive, case-insensitive or system dependent case sensitive way. A number of singleton instances are provided for the various case sensitivity options (using `IOCase`) and the reverse of those options.

  Example of a case-sensitive file extension sort using the `EXTENSION_COMPARATOR` singleton instance:

             List<File> list = ...
             ((AbstractFileComparator) ExtensionFileComparator.EXTENSION_COMPARATOR).sort(list);

  Example of a reverse case-insensitive file extension sort using the `EXTENSION_INSENSITIVE_REVERSE` singleton instance:

             File[] array = ...
             ((AbstractFileComparator) ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE).sort(array);

  Since:
    1.4
  See Also:
    Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static Comparator<File>` | `EXTENSION_COMPARATOR` Case-sensitive extension comparator instance (see `IOCase.SENSITIVE`)
    `static Comparator<File>` | `EXTENSION_INSENSITIVE_COMPARATOR` Case-insensitive extension comparator instance (see `IOCase.INSENSITIVE`)
    `static Comparator<File>` | `EXTENSION_INSENSITIVE_REVERSE` Reverse case-insensitive extension comparator instance (see `IOCase.INSENSITIVE`)
    `static Comparator<File>` | `EXTENSION_REVERSE` Reverse case-sensitive extension comparator instance (see `IOCase.SENSITIVE`)
    `static Comparator<File>` | `EXTENSION_SYSTEM_COMPARATOR` System sensitive extension comparator instance (see `IOCase.SYSTEM`)
    `static Comparator<File>` | `EXTENSION_SYSTEM_REVERSE` Reverse system sensitive path comparator instance (see `IOCase.SYSTEM`)

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ExtensionFileComparator()` Construct a case sensitive file extension comparator instance.
    `ExtensionFileComparator(IOCase caseSensitivity)` Construct a file extension comparator instance with the specified case-sensitivity.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `compare(File file1, File file2)` Compare the extensions of two files the specified case sensitivity.
    `File[]` | `sort(File... files)` Sort an array of files.
    `List<File>` | `sort(List<File> files)` Sort a List of files.
    `String` | `toString()` String representation of this file comparator.

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

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

    - ### Methods inherited from interface java.util.Comparator

      `comparing, comparing, comparingDouble, comparingInt, comparingLong, equals, naturalOrder, nullsFirst, nullsLast, reversed, reverseOrder, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong`

- - ### Field Detail

    - #### EXTENSION_COMPARATOR

          public static final Comparator<File> EXTENSION_COMPARATOR

      Case-sensitive extension comparator instance (see `IOCase.SENSITIVE`)

    - #### EXTENSION_REVERSE

          public static final Comparator<File> EXTENSION_REVERSE

      Reverse case-sensitive extension comparator instance (see `IOCase.SENSITIVE`)

    - #### EXTENSION_INSENSITIVE_COMPARATOR

          public static final Comparator<File> EXTENSION_INSENSITIVE_COMPARATOR

      Case-insensitive extension comparator instance (see `IOCase.INSENSITIVE`)

    - #### EXTENSION_INSENSITIVE_REVERSE

          public static final Comparator<File> EXTENSION_INSENSITIVE_REVERSE

      Reverse case-insensitive extension comparator instance (see `IOCase.INSENSITIVE`)

    - #### EXTENSION_SYSTEM_COMPARATOR

          public static final Comparator<File> EXTENSION_SYSTEM_COMPARATOR

      System sensitive extension comparator instance (see `IOCase.SYSTEM`)

    - #### EXTENSION_SYSTEM_REVERSE

          public static final Comparator<File> EXTENSION_SYSTEM_REVERSE

      Reverse system sensitive path comparator instance (see `IOCase.SYSTEM`)

  - ### Constructor Detail

    - #### ExtensionFileComparator

          public ExtensionFileComparator()

      Construct a case sensitive file extension comparator instance.

    - #### ExtensionFileComparator

          public ExtensionFileComparator(IOCase caseSensitivity)

      Construct a file extension comparator instance with the specified case-sensitivity.
      Parameters:
        `caseSensitivity` - how to handle case sensitivity, null means case-sensitive

  - ### Method Detail

    - #### compare

          public int compare(File file1,
                             File file2)

      Compare the extensions of two files the specified case sensitivity.
      Specified by:
        `compare` in interface `Comparator<File>`
      Parameters:
        `file1` - The first file to compare
        `file2` - The second file to compare
      Returns:
        a negative value if the first file's extension is less than the second, zero if the extensions are the same and a positive value if the first files extension is greater than the second file.

    - #### toString

          public String toString()

      String representation of this file comparator.
      Returns:
        String representation of this file comparator

    - #### sort

          public File[] sort(File... files)

      Sort an array of files.

      This method uses `Arrays.sort(Object[], Comparator)` and returns the original array.

      Parameters:
        `files` - The files to sort, may be null
      Returns:
        The sorted array
      Since:
        2.0

    - #### sort

          public List<File> sort(List<File> files)

      Sort a List of files.

      This method uses `Collections.sort(List, Comparator)` and returns the original list.

      Parameters:
        `files` - The files to sort, may be null
      Returns:
        The sorted list
      Since:
        2.0

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