com.google.common.primitives
Class Longs

java.lang.Object
  com.google.common.primitives.Longs

public final class Longs
extends Object

Static utility methods pertaining to long primitives, that are not already found in either Long or Arrays.

Since:

2009.09.15 tentative

Author:

Kevin Bourrillion

Field Summary

static int

BYTES The number of bytes required to represent a primitive long value.

Method Summary

static List<Long>	asList(long... backingArray) Returns a fixed-size list backed by the specified array, similar to Arrays.asList(Object[]).
static int	compare(long a, long b) Compares the two specified long values.
static long[]	concat(long[]... arrays) Returns the values from each provided array combined into a single array.
static boolean	contains(long[] array, long target) Returns true if target is present as an element anywhere in array.
static long[]	ensureCapacity(long[] array, int minLength, int padding) Returns an array containing the same values as array, but guaranteed to be of a specified minimum length.
static long	fromByteArray(byte[] bytes) Returns the long value whose big-endian representation is stored in the first 8 bytes of bytes; equivalent to ByteBuffer.wrap(bytes).getLong().
static int	hashCode(long value) Returns a hash code for value; equal to the result of invoking ((Long) value).hashCode().
static int	indexOf(long[] array, long target) Returns the index of the first appearance of the value target in array.
static int	indexOf(long[] array, long[] target) Returns the start position of the first occurrence of the specified target within array, or -1 if there is no such occurrence.
static String	join(String separator, long... array) Returns a string containing the supplied long values separated by separator.
static int	lastIndexOf(long[] array, long target) Returns the index of the last appearance of the value target in array.
static Comparator<long[]>	lexicographicalComparator() Returns a comparator that compares two long arrays lexicographically.
static long	max(long... array) Returns the greatest value present in array.
static long	min(long... array) Returns the least value present in array.
static long[]	toArray(Collection<Long> collection) Copies a collection of Long instances into a new array of primitive long values.
static byte[]	toByteArray(long value) Returns a big-endian representation of value in an 8-element byte array; equivalent to ByteBuffer.allocate(8).putLong(value).array().

Methods inherited from class java.lang.Object

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

Field Detail

BYTES

public static final int BYTES

The number of bytes required to represent a primitive long value.

See Also:

Constant Field Values

Method Detail

hashCode

public static int hashCode(long value)

Returns a hash code for value; equal to the result of invoking ((Long) value).hashCode().

Parameters:

value - a primitive long value

Returns:

a hash code for the value

compare

public static int compare(long a,
                          long b)

Compares the two specified long values. The sign of the value returned is the same as that of ((Long) a).compareTo(b).

Parameters:

a - the first long to compare

b - the second long to compare

Returns:

a negative value if a is less than b; a positive value if a is greater than b; or zero if they are equal

contains

public static boolean contains(long[] array,
                               long target)

Returns true if target is present as an element anywhere in array.

Parameters:

array - an array of long values, possibly empty

target - a primitive long value

Returns:

true if array[i] == target for some value of i

indexOf

public static int indexOf(long[] array,
                          long target)

Returns the index of the first appearance of the value target in array.

Parameters:

array - an array of long values, possibly empty

target - a primitive long value

Returns:

the least index i for which array[i] == target, or -1 if no such index exists.

indexOf

public static int indexOf(long[] array,
                          long[] target)

Returns the start position of the first occurrence of the specified target within array, or -1 if there is no such occurrence.

More formally, returns the lowest index i such that java.util.Arrays.copyOfRange(array, i, i + target.length) contains exactly the same elements as target.

Parameters:

array - the array to search for the sequence target

target - the array to search for as a sub-sequence of array

lastIndexOf

public static int lastIndexOf(long[] array,
                              long target)

Returns the index of the last appearance of the value target in array.

Parameters:

array - an array of long values, possibly empty

target - a primitive long value

Returns:

the greatest index i for which array[i] == target, or -1 if no such index exists.

min

public static long min(long... array)

Returns the least value present in array.

Parameters:

array - a nonempty array of long values

Returns:

the value present in array that is less than or equal to every other value in the array

Throws:

IllegalArgumentException - if array is empty

max

public static long max(long... array)

Returns the greatest value present in array.

Parameters:

array - a nonempty array of long values

Returns:

the value present in array that is greater than or equal to every other value in the array

Throws:

IllegalArgumentException - if array is empty

concat

public static long[] concat(long[]... arrays)

Returns the values from each provided array combined into a single array. For example, concat(new long[] {a, b}, new long[] {}, new long[] {c} returns the array {a, b, c}.

Parameters:

arrays - zero or more long arrays

Returns:

a single array containing all the values from the source arrays, in order

toByteArray

public static byte[] toByteArray(long value)

Returns a big-endian representation of value in an 8-element byte array; equivalent to ByteBuffer.allocate(8).putLong(value).array(). For example, the input value 0x1213141516171819L would yield the byte array {0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19}.

If you need to convert and concatenate several values (possibly even of different types), use a shared ByteBuffer instance, or use ByteStreams.newDataOutput() to get a growable buffer.

Warning: do not use this method in GWT. It returns wrong answers.

fromByteArray

public static long fromByteArray(byte[] bytes)

Returns the long value whose big-endian representation is stored in the first 8 bytes of bytes; equivalent to ByteBuffer.wrap(bytes).getLong(). For example, the input byte array {0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19} would yield the long value 0x1213141516171819L.

Arguably, it's preferable to use ByteBuffer; that library exposes much more flexibility at little cost in readability.

Warning: do not use this method in GWT. It returns wrong answers.

Throws:

IllegalArgumentException - if bytes has fewer than 8 elements

ensureCapacity

public static long[] ensureCapacity(long[] array,
                                    int minLength,
                                    int padding)

Returns an array containing the same values as array, but guaranteed to be of a specified minimum length. If array already has a length of at least minLength, it is returned directly. Otherwise, a new array of size minLength + padding is returned, containing the values of array, and zeroes in the remaining places.

Parameters:

array - the source array

minLength - the minimum length the returned array must guarantee

padding - an extra amount to "grow" the array by if growth is necessary

Returns:

an array containing the values of array, with guaranteed minimum length minLength

Throws:

IllegalArgumentException - if minLength or padding is negative

join

public static String join(String separator,
                          long... array)

Returns a string containing the supplied long values separated by separator. For example, join("-", 1L, 2L, 3L) returns the string "1-2-3".

Parameters:

separator - the text that should appear between consecutive values in the resulting string (but not at the start or end)

array - an array of long values, possibly empty

lexicographicalComparator

public static Comparator<long[]> lexicographicalComparator()

Returns a comparator that compares two long arrays lexicographically. That is, it compares, using compare(long, long)), the first pair of values that follow any common prefix, or when one array is a prefix of the other, treats the shorter array as the lesser. For example, [] < [1L] < [1L, 2L] < [2L].

The returned comparator is inconsistent with Object.equals(Object) (since arrays support only identity equality), but it is consistent with Arrays.equals(long[], long[]).

Since:

2010.01.04 tentative

See Also:

Lexicographical order article at Wikipedia

toArray

public static long[] toArray(Collection<Long> collection)

Copies a collection of Long instances into a new array of primitive long values.

Elements are copied from the argument collection as if by collection.toArray(). Calling this method is as thread-safe as calling that method.

Parameters:

collection - a collection of Long objects

Returns:

an array containing the same values as collection, in the same order, converted to primitives

Throws:

NullPointerException - if collection or any of its elements is null

asList

public static List<Long> asList(long... backingArray)

Returns a fixed-size list backed by the specified array, similar to Arrays.asList(Object[]). The list supports List.set(int, Object), but any attempt to set a value to null will result in a NullPointerException.

The returned list maintains the values, but not the identities, of Long objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified.

Parameters:

backingArray - the array to back the list

Returns:

a list view of the array