Package 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

    • 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

      • 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

      • putUnencodedChars

        Hasher putUnencodedChars​(java.lang.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

        @Deprecated
Hasher putString​(java.lang.CharSequence charSequence)
        Deprecated.
        Use putUnencodedChars(java.lang.CharSequence) instead. This method is scheduled for removal in Guava 16.0.
        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:
        putString in interface PrimitiveSink

      • putString

        Hasher putString​(java.lang.CharSequence charSequence,
                 java.nio.charset.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.