@Beta @CanIgnoreReturnValue public interface Hasher extends PrimitiveSink
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.
| Modifier and Type | Method and Description |
|---|---|
HashCode |
hash()
Computes a hash code based on the data that have been provided to this hasher.
|
int |
hashCode()
Deprecated.
This returns
Object.hashCode(); you almost certainly mean to call hash().asInt(). |
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 |
putBytes(ByteBuffer bytes)
Puts the remaining bytes of a byte buffer 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. |
Hasher putByte(byte b)
PrimitiveSinkputByte in interface PrimitiveSinkb - a byteHasher putBytes(byte[] bytes)
PrimitiveSinkputBytes in interface PrimitiveSinkbytes - a byte arrayHasher putBytes(byte[] bytes, int off, int len)
PrimitiveSinkbytes[off] is the first byte written,
bytes[off + len - 1] is the last.putBytes in interface PrimitiveSinkbytes - a byte arrayoff - the start offset in the arraylen - the number of bytes to writeHasher putBytes(ByteBuffer bytes)
PrimitiveSinkbytes.position() is the first
byte written, bytes.limit() - 1 is the last. The position of the buffer will be equal
to the limit when this method returns.putBytes in interface PrimitiveSinkbytes - a byte bufferHasher putShort(short s)
PrimitiveSinkputShort in interface PrimitiveSinkHasher putInt(int i)
PrimitiveSinkputInt in interface PrimitiveSinkHasher putLong(long l)
PrimitiveSinkputLong in interface PrimitiveSinkHasher putFloat(float f)
putInt(Float.floatToRawIntBits(f)).putFloat in interface PrimitiveSinkHasher putDouble(double d)
putLong(Double.doubleToRawLongBits(d)).putDouble in interface PrimitiveSinkHasher putBoolean(boolean b)
putByte(b ? (byte) 1 : (byte) 0).putBoolean in interface PrimitiveSinkHasher putChar(char c)
PrimitiveSinkputChar in interface PrimitiveSinkHasher putUnencodedChars(CharSequence charSequence)
char value in the CharSequence, in order. In
other words, no character encoding is performed; the low byte and high byte of each char are hashed directly (in that order). The input must not be updated while this method is
in progress.
Warning: This method will produce different output than most other languages do when
running the same hash function on the equivalent input. For cross-language compatibility, use
putString(java.lang.CharSequence, java.nio.charset.Charset), usually with a charset of UTF-8. For other use cases, use putUnencodedChars.
putUnencodedChars in interface PrimitiveSinkHasher putString(CharSequence charSequence, Charset charset)
putBytes(charSequence.toString().getBytes(charset)).
Warning: This method, which reencodes the input before hashing it, is useful only for
cross-language compatibility. For other use cases, prefer putUnencodedChars(java.lang.CharSequence), which is
faster, produces the same output across Java releases, and hashes every char in the
input, even if some are invalid.
putString in interface PrimitiveSink<T> Hasher putObject(T instance, Funnel<? super T> funnel)
funnel.funnel(object, this).HashCode hash()
@Deprecated int hashCode()
Object.hashCode(); you almost certainly mean to call hash().asInt().HashMap.
The general contract of hashCode is:
hashCode method
must consistently return the same integer, provided no information
used in equals comparisons on the object is modified.
This integer need not remain consistent from one execution of an
application to another execution of the same application.
equals(Object)
method, then calling the hashCode method on each of
the two objects must produce the same integer result.
Object.equals(java.lang.Object)
method, then calling the hashCode method on each of the
two objects must produce distinct integer results. However, the
programmer should be aware that producing distinct integer results
for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by
class Object does return distinct integers for distinct
objects. (This is typically implemented by converting the internal
address of the object into an integer, but this implementation
technique is not required by the
Java™ programming language.)
hashCode in class ObjectObject.equals(java.lang.Object),
System.identityHashCode(java.lang.Object)Copyright © 2010–2020. All rights reserved.