guava/src/com/google/common/hash/Hasher.java

/*
 * 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.
 *
 * <p><b>Warning:</b> The result of calling any methods after calling {@link #hash} is undefined.
 *
 * <p><b>Warning:</b> 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.
 *
 * <p><b>Warning:</b> 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:
 *
 * <pre>{@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()
 * }</pre>
 *
 * <p>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 <i>complete</i>
 * 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.
   *
   * <p><b>Warning:</b> 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))}.
   *
   * <p><b>Warning:</b> 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)}. */
  <T> Hasher putObject(T instance, Funnel<? super T> 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();
}