com.google.common.hash

Class HashCode

java.lang.Object

com.google.common.hash.HashCode

@Beta
public abstract class HashCode
extends Object

An immutable hash code of arbitrary bit length.

Since:

11.0

Author:

Dimitris Andreou, Kurt Alfred Kluever

Method Summary

Methods

Modifier and Type	Method and Description
abstract byte[]	asBytes() Returns the value of this hash code as a byte array.
abstract int	asInt() Returns the first four bytes of this hashcode's bytes, converted to an int value in little-endian order.
abstract long	asLong() Returns the first eight bytes of this hashcode's bytes, converted to a long value in little-endian order.
abstract int	bits() Returns the number of bits in this hash code; a positive multiple of 8.
boolean	equals(Object object) Indicates whether some other object is "equal to" this one.
static HashCode	fromBytes(byte[] bytes) Creates a HashCode from a byte array.
static HashCode	fromInt(int hash) Creates a 32-bit HashCode representation of the given int value.
static HashCode	fromLong(long hash) Creates a 64-bit HashCode representation of the given long value.
static HashCode	fromString(String string) Creates a HashCode from a hexadecimal (base 16) encoded string.
int	hashCode() Returns a "Java hash code" for this HashCode instance; this is well-defined (so, for example, you can safely put HashCode instances into a HashSet) but is otherwise probably not what you want to use.
abstract long	padToLong() If this hashcode has enough bits, returns asLong(), otherwise returns a long value with asBytes() as the least-significant bytes and 0x00 as the remaining most-significant bytes.
String	toString() Returns a string containing each byte of asBytes(), in order, as a two-digit unsigned hexadecimal number in lower case.
int	writeBytesTo(byte[] dest, int offset, int maxLength) Copies bytes from this hash code into dest.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

asInt

public abstract int asInt()

Returns the first four bytes of this hashcode's bytes, converted to an int value in little-endian order.

Throws:

IllegalStateException - if bits() < 32

asLong

public abstract long asLong()

Returns the first eight bytes of this hashcode's bytes, converted to a long value in little-endian order.

Throws:

IllegalStateException - if bits() < 64

padToLong

public abstract long padToLong()

If this hashcode has enough bits, returns asLong(), otherwise returns a long value with asBytes() as the least-significant bytes and 0x00 as the remaining most-significant bytes.

Since:

14.0 (since 11.0 as Hashing.padToLong(HashCode))

asBytes

public abstract byte[] asBytes()

Returns the value of this hash code as a byte array. The caller may modify the byte array; changes to it will not be reflected in this HashCode object or any other arrays returned by this method.

fromInt

public static HashCode fromInt(int hash)

Creates a 32-bit HashCode representation of the given int value. The underlying bytes are interpreted in little endian order.

Since:

15.0 (since 12.0 in HashCodes)

fromLong

public static HashCode fromLong(long hash)

Creates a 64-bit HashCode representation of the given long value. The underlying bytes are interpreted in little endian order.

Since:

15.0 (since 12.0 in HashCodes)

fromBytes

public static HashCode fromBytes(byte[] bytes)

Creates a HashCode from a byte array. The array is defensively copied to preserve the immutability contract of HashCode. The array cannot be empty.

Since:

15.0 (since 12.0 in HashCodes)

bits

public abstract int bits()

Returns the number of bits in this hash code; a positive multiple of 8.

fromString

public static HashCode fromString(String string)

Creates a HashCode from a hexadecimal (base 16) encoded string. The string must be at least 2 characters long, and contain only valid, lower-cased hexadecimal characters.

This method accepts the exact format generated by toString(). If you require more lenient base 16 decoding, please use BaseEncoding.decode(java.lang.CharSequence) (and pass the result to fromBytes(byte[])).

Since:

15.0

writeBytesTo

public final int writeBytesTo(byte[] dest,
               int offset,
               int maxLength)

Copies bytes from this hash code into dest.

Parameters:

dest - the byte array into which the hash code will be written

offset - the start offset in the data

maxLength - the maximum number of bytes to write

Returns:

the number of bytes written to dest

Throws:

IndexOutOfBoundsException - if there is not enough room in dest

equals

public final boolean equals(@Nullable
             Object object)

Description copied from class: java.lang.Object

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
• For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

Overrides:

equals in class Object

Parameters:

object - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Object.hashCode(), HashMap

hashCode

public final int hashCode()

Returns a "Java hash code" for this HashCode instance; this is well-defined (so, for example, you can safely put HashCode instances into a HashSet) but is otherwise probably not what you want to use.

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

toString

public final String toString()

Returns a string containing each byte of asBytes(), in order, as a two-digit unsigned hexadecimal number in lower case.

Note that if the output is considered to be a single hexadecimal number, this hash code's bytes are the big-endian representation of that number. This may be surprising since everything else in the hashing API uniformly treats multibyte values as little-endian. But this format conveniently matches that of utilities such as the UNIX md5sum command.

To create a HashCode from its string representation, see fromString(java.lang.String).

Overrides:

toString in class Object

Returns:

a string representation of the object.