com.google.common.hash.Hasher Maven / Gradle / Ivy
/*
* 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 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
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 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.
* The input must not be updated while this method is in progress.
*
* @since 15.0 (since 11.0 as putString(CharSequence)).
*/
@Override Hasher putUnencodedChars(CharSequence charSequence);
/**
* Equivalent to {@code putBytes(charSequence.toString().getBytes(charset))}.
*/
@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();
}