Module org.jgrapht.core

Package org.jgrapht.util

Class CollectionUtil

java.lang.Object

org.jgrapht.util.CollectionUtil

public class CollectionUtil
extends Object

Utility class to create Collection instances.

Author:

Hannes Wellmann

Method Summary

Modifier and Type	Method	Description
static <E> E	getElement(Iterable<E> iterable, int index)	Returns from the given Iterable the element with the given index.
static <K, V> HashMap<K,V>	newHashMapWithExpectedSize(int expectedSize)	Returns a HashMap with an initial capacity that is sufficient to hold expectedSize mappings without rehashing its internal backing storage.
static <E> HashSet<E>	newHashSetWithExpectedSize(int expectedSize)	Returns a HashSet with an initial capacity that is sufficient to hold expectedSize elements without rehashing its internal backing storage.
static <K, V> LinkedHashMap<K,V>	newLinkedHashMapWithExpectedSize(int expectedSize)	Returns a LinkedHashMap with an initial capacity that is sufficient to hold expectedSize mappings without rehashing its internal backing storage.
static <E> LinkedHashSet<E>	newLinkedHashSetWithExpectedSize(int expectedSize)	Returns a LinkedHashSet with an initial capacity that is sufficient to hold expectedSize elements without rehashing its internal backing storage.

Methods inherited from class java.lang.Object

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

Method Details

newHashMapWithExpectedSize

public static <K,
V> HashMap<K,V> newHashMapWithExpectedSize(int expectedSize)

Returns a HashMap with an initial capacity that is sufficient to hold expectedSize mappings without rehashing its internal backing storage.

The returned HashMap has a capacity that is the specified expected size divided by the load factor of the Map, which is sufficient to hold expectedSize mappings without rehashing. As the Javadoc of HashMap states: "If the initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operations will ever occur".

Type Parameters:

K - the type of keys in the returned HashMap

V - the type of values in the returned HashMap

Parameters:

expectedSize - of mappings that will be put into the returned HashMap

Returns:

an empty HashMap with sufficient capacity to hold expectedSize mappings

See Also:

• HashMap

newLinkedHashMapWithExpectedSize

public static <K,
V> LinkedHashMap<K,V> newLinkedHashMapWithExpectedSize(int expectedSize)

Returns a LinkedHashMap with an initial capacity that is sufficient to hold expectedSize mappings without rehashing its internal backing storage.

Because LinkedHashMap extends HashMap it inherits the issue that the capacity is not equivalent to the number of mappings it can hold without rehashing. See newHashMapWithExpectedSize(int) for details.

Type Parameters:

K - the type of keys in the returned LinkedHashMap

V - the type of values in the returned LinkedHashMap

Parameters:

expectedSize - of mappings that will be put into the returned LinkedHashMap

Returns:

an empty LinkedHashMap with sufficient capacity to hold expectedSize mappings

See Also:

• HashMap

newHashSetWithExpectedSize

public static <E> HashSet<E> newHashSetWithExpectedSize(int expectedSize)

Returns a HashSet with an initial capacity that is sufficient to hold expectedSize elements without rehashing its internal backing storage.

Because a HashSet is backed by a HashMap it inherits the issue that the capacity is not equivalent to the number of elements it can hold without rehashing. See newHashMapWithExpectedSize(int) for details.

Type Parameters:

E - the type of elements in the returned HashSet

Parameters:

expectedSize - of elements that will be add to the returned HashSet

Returns:

an empty HashSet with sufficient capacity to hold expectedSize elements

See Also:

• HashMap

newLinkedHashSetWithExpectedSize

public static <E> LinkedHashSet<E> newLinkedHashSetWithExpectedSize(int expectedSize)

Returns a LinkedHashSet with an initial capacity that is sufficient to hold expectedSize elements without rehashing its internal backing storage.

Because a LinkedHashSet is backed by a HashMap it inherits the issue that the capacity is not equivalent to the number of elements it can hold without rehashing. See newHashMapWithExpectedSize(int) for details.

Type Parameters:

E - the type of elements in the returned LinkedHashSet

Parameters:

expectedSize - of elements that will be add to the returned LinkedHashSet

Returns:

an empty LinkedHashSet with sufficient capacity to hold expectedSize elements

See Also:

• HashMap

getElement

public static <E> E getElement(Iterable<E> iterable,
 int index)

Returns from the given Iterable the element with the given index.

The order to which the index applies is that defined by the Iterable.iterator().

Type Parameters:

E - the type of elements in the Iterable

Parameters:

iterable - the Iterable from which the element at index is returned

index - the index of the returned element

Returns:

the element with index in the iterable