com.diffplug.common.hash.Hasher Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of durian-io Show documentation
Durian - Guava's spikier (unofficial) cousin
There is a newer version: 1.2.0
/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2016 DiffPlug.
 *
 * 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.diffplug.common.hash;

import java.nio.charset.Charset;

import javax.annotation.CheckReturnValue;

import com.diffplug.common.annotations.Beta;

/**
 * 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.
	 */
	@CheckReturnValue
	HashCode hash();

	/**
	 * {@inheritDoc}
	 *
	 * @deprecated This returns {@link Object#hashCode()}; you almost certainly mean to call
	 *     {@code hash().asInt()}.
	 */
	@Override
	@Deprecated
	int hashCode();
}