com.google.common.hash

Interface Hasher

All Superinterfaces:

PrimitiveSink

@Beta
public interface Hasher
extends PrimitiveSink

A PrimitiveSink that can compute a hash code after reading the input. Each hasher should translate all multibyte values (putInt(int), putLong(long), etc) to bytes in little-endian order.

Warning: The result of calling any methods after calling hash() is undefined.

Warning: Using a specific character encoding when hashing a CharSequence with putString(CharSequence, Charset) is generally only useful for cross-language compatibility (otherwise prefer putUnencodedChars(java.lang.CharSequence)). However, the character encodings must be identical across languages. Also beware that Charset definitions may occasionally change between Java releases.

Warning: Chunks of data that are put into the Hasher are not delimited. The resulting HashCode is dependent only on the bytes inserted, and the order in which they were inserted, not how those bytes were chunked into discrete put() operations. For example, the following three expressions all generate colliding hash codes:

   newHasher().putByte(b1).putByte(b2).putByte(b3).hash()
   newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash()
   newHasher().putBytes(new byte[] { b1, b2, b3 }).hash()

If you wish to avoid this, you should either prepend or append the size of each chunk. Keep in mind that when dealing with char sequences, the encoded form of two concatenated char sequences is not equivalent to the concatenation of their encoded form. Therefore, putString(CharSequence, Charset) should only be used consistently with complete sequences and not broken into chunks.

Since:

11.0

Author:

Kevin Bourrillion

Method Summary

Methods

Modifier and Type	Method and Description
HashCode	hash() Computes a hash code based on the data that have been provided to this hasher.
Hasher	putBoolean(boolean b) Equivalent to putByte(b ? (byte) 1 : (byte) 0).
Hasher	putByte(byte b) Puts a byte into this sink.
Hasher	putBytes(byte[] bytes) Puts an array of bytes into this sink.
Hasher	putBytes(byte[] bytes, int off, int len) Puts a chunk of an array of bytes into this sink.
Hasher	putChar(char c) Puts a character into this sink.
Hasher	putDouble(double d) Equivalent to putLong(Double.doubleToRawLongBits(d)).
Hasher	putFloat(float f) Equivalent to putInt(Float.floatToRawIntBits(f)).
Hasher	putInt(int i) Puts an int into this sink.
Hasher	putLong(long l) Puts a long into this sink.
<T> Hasher	putObject(T instance, Funnel<? super T> funnel) A simple convenience for funnel.funnel(object, this).
Hasher	putShort(short s) Puts a short into this sink.
Hasher	putString(CharSequence charSequence, Charset charset) Equivalent to putBytes(charSequence.toString().getBytes(charset)).
Hasher	putUnencodedChars(CharSequence charSequence) Equivalent to processing each char value in the CharSequence, in order.

Method Detail

putByte

Hasher putByte(byte b)

Description copied from interface: PrimitiveSink

Puts a byte into this sink.

Specified by:

putByte in interface PrimitiveSink

Parameters:

b - a byte

Returns:

this instance

putBytes

Hasher putBytes(byte[] bytes)

Description copied from interface: PrimitiveSink

Puts an array of bytes into this sink.

Specified by:

putBytes in interface PrimitiveSink

Parameters:

bytes - a byte array

Returns:

this instance

putBytes

Hasher putBytes(byte[] bytes,
              int off,
              int len)

Description copied from interface: PrimitiveSink

Puts a chunk of an array of bytes into this sink. bytes[off] is the first byte written, bytes[off + len - 1] is the last.

Specified by:

putBytes in interface PrimitiveSink

Parameters:

bytes - a byte array

off - the start offset in the array

len - the number of bytes to write

Returns:

this instance

putShort

Hasher putShort(short s)

Description copied from interface: PrimitiveSink

Puts a short into this sink.

Specified by:

putShort in interface PrimitiveSink

putInt

Hasher putInt(int i)

Description copied from interface: PrimitiveSink

Puts an int into this sink.

Specified by:

putInt in interface PrimitiveSink

putLong

Hasher putLong(long l)

Description copied from interface: PrimitiveSink

Puts a long into this sink.

Specified by:

putLong in interface PrimitiveSink

putFloat

Hasher putFloat(float f)

Equivalent to putInt(Float.floatToRawIntBits(f)).

Specified by:

putFloat in interface PrimitiveSink

putDouble

Hasher putDouble(double d)

Equivalent to putLong(Double.doubleToRawLongBits(d)).

Specified by:

putDouble in interface PrimitiveSink

putBoolean

Hasher putBoolean(boolean b)

Equivalent to putByte(b ? (byte) 1 : (byte) 0).

Specified by:

putBoolean in interface PrimitiveSink

putChar

Hasher putChar(char c)

Description copied from interface: PrimitiveSink

Puts a character into this sink.

Specified by:

putChar in interface PrimitiveSink

putUnencodedChars

Hasher putUnencodedChars(CharSequence charSequence)

Equivalent to processing each char value in the CharSequence, in order. The input must not be updated while this method is in progress.

Specified by:

putUnencodedChars in interface PrimitiveSink

Since:

15.0 (since 11.0 as putString(CharSequence)).

putString

Hasher putString(CharSequence charSequence,
               Charset charset)

Equivalent to putBytes(charSequence.toString().getBytes(charset)).

Specified by:

putString in interface PrimitiveSink

putObject

<T> Hasher putObject(T instance,
                   Funnel<? super T> funnel)

A simple convenience for funnel.funnel(object, this).

hash

HashCode hash()

Computes a hash code based on the data that have been provided to this hasher. The result is unspecified if this method is called more than once on the same instance.