com.google.common.hash.Hasher Maven / Gradle / Ivy
Show all versions of guava Show documentation
/*
* Copyright (C) 2011 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.hash;
import com.google.common.annotations.Beta;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
/**
* A {@link PrimitiveSink} that can compute a hash code after reading the input. Each hasher should
* translate all multibyte values ({@link #putInt(int)}, {@link #putLong(long)}, etc) to bytes in
* little-endian order.
*
* Warning: The result of calling any methods after calling {@link #hash} is undefined.
*
*
Warning: Using a specific character encoding when hashing a {@link CharSequence} with
* {@link #putString(CharSequence, Charset)} is generally only useful for cross-language
* compatibility (otherwise prefer {@link #putUnencodedChars}). However, the character encodings
* must be identical across languages. Also beware that {@link Charset} definitions may occasionally
* change between Java releases.
*
*
Warning: Chunks of data that are put into the {@link Hasher} are not delimited. The
* resulting {@link 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:
*
*
{@code
* 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, {@link
* #putString(CharSequence, Charset)} should only be used consistently with complete
* sequences and not broken into chunks.
*
* @author Kevin Bourrillion
* @since 11.0
*/
@Beta
@CanIgnoreReturnValue
public interface Hasher extends PrimitiveSink {
@Override
Hasher putByte(byte b);
@Override
Hasher putBytes(byte[] bytes);
@Override
Hasher putBytes(byte[] bytes, int off, int len);
@Override
Hasher putBytes(ByteBuffer bytes);
@Override
Hasher putShort(short s);
@Override
Hasher putInt(int i);
@Override
Hasher putLong(long l);
/** Equivalent to {@code putInt(Float.floatToRawIntBits(f))}. */
@Override
Hasher putFloat(float f);
/** Equivalent to {@code putLong(Double.doubleToRawLongBits(d))}. */
@Override
Hasher putDouble(double d);
/** Equivalent to {@code putByte(b ? (byte) 1 : (byte) 0)}. */
@Override
Hasher putBoolean(boolean b);
@Override
Hasher putChar(char c);
/**
* Equivalent to processing each {@code char} value in the {@code CharSequence}, in order. In
* other words, no character encoding is performed; the low byte and high byte of each {@code
* 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
* {@link #putString}, usually with a charset of UTF-8. For other use cases, use {@code
* putUnencodedChars}.
*
* @since 15.0 (since 11.0 as putString(CharSequence)).
*/
@Override
Hasher putUnencodedChars(CharSequence charSequence);
/**
* Equivalent to {@code 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 {@link #putUnencodedChars}, which is
* faster, produces the same output across Java releases, and hashes every {@code char} in the
* input, even if some are invalid.
*/
@Override
Hasher putString(CharSequence charSequence, Charset charset);
/** A simple convenience for {@code funnel.funnel(object, this)}. */
Hasher putObject(T instance, Funnel funnel);
/**
* 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.
*/
HashCode hash();
/**
* {@inheritDoc}
*
* @deprecated This returns {@link Object#hashCode()}; you almost certainly mean to call {@code
* hash().asInt()}.
*/
@Override
@Deprecated
int hashCode();
}