Package org.apache.lucene.util

# Class CollectionUtil

java.lang.Object
org.apache.lucene.util.CollectionUtil

public final class CollectionUtil extends Object
Methods for manipulating (sorting) and creating collections. Sort methods work directly on the supplied lists and don't copy to/from arrays before/after. For medium size collections as used in the Lucene indexer that is much more efficient.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

## Method Summary

Modifier and Type
Method
Description
`static <T extends Comparable<? super T>>
void`
`introSort(List<T> list)`
Sorts the given random access `List` in natural order.
`static <T> void`
`introSort(List<T> list, Comparator<? super T> comp)`
Sorts the given random access `List` using the `Comparator`.
`static <K, V> HashMap<K,V>`
`newHashMap(int size)`
Returns a new `HashMap` sized to contain `size` items without resizing the internal array.
`static <E> HashSet<E>`
`newHashSet(int size)`
Returns a new `HashSet` sized to contain `size` items without resizing the internal array.
`static <T extends Comparable<? super T>>
void`
`timSort(List<T> list)`
Sorts the given random access `List` in natural order.
`static <T> void`
`timSort(List<T> list, Comparator<? super T> comp)`
Sorts the given random access `List` using the `Comparator`.

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

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

## Method Details

### newHashMap

public static <K, V> HashMap<K,V> newHashMap(int size)
Returns a new `HashMap` sized to contain `size` items without resizing the internal array.

### newHashSet

public static <E> HashSet<E> newHashSet(int size)
Returns a new `HashSet` sized to contain `size` items without resizing the internal array.

### introSort

public static <T> void introSort(List<T> list, Comparator<? super T> comp)
Sorts the given random access `List` using the `Comparator`. The list must implement `RandomAccess`. This method uses the intro sort algorithm, but falls back to insertion sort for small lists.

Throws:
  `IllegalArgumentException` - if list is e.g. a linked list without random access.
See Also:
  - `IntroSorter`

### introSort

public static <T extends Comparable<? super T>> void introSort(List<T> list)
Sorts the given random access `List` in natural order. The list must implement `RandomAccess`. This method uses the intro sort algorithm, but falls back to insertion sort for small lists.

Throws:
  `IllegalArgumentException` - if list is e.g. a linked list without random access.
See Also:
  - `IntroSorter`

### timSort

public static <T> void timSort(List<T> list, Comparator<? super T> comp)
Sorts the given random access `List` using the `Comparator`. The list must implement `RandomAccess`. This method uses the Tim sort algorithm, but falls back to binary sort for small lists.

Throws:
  `IllegalArgumentException` - if list is e.g. a linked list without random access.
See Also:
  - `TimSorter`

### timSort

public static <T extends Comparable<? super T>> void timSort(List<T> list)
Sorts the given random access `List` in natural order. The list must implement `RandomAccess`. This method uses the Tim sort algorithm, but falls back to binary sort for small lists.

Throws:
  `IllegalArgumentException` - if list is e.g. a linked list without random access.
See Also:
  - `TimSorter`