1   /*
2    * Copyright (C) 2011 The Guava Authors
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5    * in compliance with the License. You may obtain a copy of the License at
6    *
7    * http://www.apache.org/licenses/LICENSE-2.0
8    *
9    * Unless required by applicable law or agreed to in writing, software distributed under the License
10   * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11   * or implied. See the License for the specific language governing permissions and limitations under
12   * the License.
13   */
14  
15  package com.google.common.hash;
16  
17  import com.google.common.annotations.Beta;
18  
19  import java.nio.charset.Charset;
20  
21  /**
22   * A {@link PrimitiveSink} that can compute a hash code after reading the input. Each hasher should
23   * translate all multibyte values ({@link #putInt(int)}, {@link #putLong(long)}, etc) to bytes
24   * in little-endian order.
25   *
26   * <p><b>Warning:</b> The result of calling any methods after calling {@link #hash} is undefined.
27   *
28   * <p><b>Warning:</b> Using a specific character encoding when hashing a {@link CharSequence} with
29   * {@link #putString(CharSequence, Charset)} is generally only useful for cross-language
30   * compatibility (otherwise prefer {@link #putUnencodedChars}). However, the character encodings
31   * must be identical across languages. Also beware that {@link Charset} definitions may occasionally
32   * change between Java releases.
33   *
34   * <p><b>Warning:</b> Chunks of data that are put into the {@link Hasher} are not delimited.
35   * The resulting {@link HashCode} is dependent only on the bytes inserted, and the order in which
36   * they were inserted, not how those bytes were chunked into discrete put() operations. For example,
37   * the following three expressions all generate colliding hash codes: <pre>   {@code
38   *
39   *   newHasher().putByte(b1).putByte(b2).putByte(b3).hash()
40   *   newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash()
41   *   newHasher().putBytes(new byte[] { b1, b2, b3 }).hash()}</pre>
42   *
43   * <p>If you wish to avoid this, you should either prepend or append the size of each chunk. Keep in
44   * mind that when dealing with char sequences, the encoded form of two concatenated char sequences
45   * is not equivalent to the concatenation of their encoded form. Therefore,
46   * {@link #putString(CharSequence, Charset)} should only be used consistently with <i>complete</i>
47   * sequences and not broken into chunks.
48   *
49   * @author Kevin Bourrillion
50   * @since 11.0
51   */
52  @Beta
53  public interface Hasher extends PrimitiveSink {
54    @Override Hasher putByte(byte b);
55    @Override Hasher putBytes(byte[] bytes);
56    @Override Hasher putBytes(byte[] bytes, int off, int len);
57    @Override Hasher putShort(short s);
58    @Override Hasher putInt(int i);
59    @Override Hasher putLong(long l);
60  
61    /**
62     * Equivalent to {@code putInt(Float.floatToRawIntBits(f))}.
63     */
64    @Override Hasher putFloat(float f);
65  
66    /**
67     * Equivalent to {@code putLong(Double.doubleToRawLongBits(d))}.
68     */
69    @Override Hasher putDouble(double d);
70  
71    /**
72     * Equivalent to {@code putByte(b ? (byte) 1 : (byte) 0)}.
73     */
74    @Override Hasher putBoolean(boolean b);
75    @Override Hasher putChar(char c);
76  
77    /**
78     * Equivalent to processing each {@code char} value in the {@code CharSequence}, in order.
79     * The input must not be updated while this method is in progress.
80     *
81     * @since 15.0 (since 11.0 as putString(CharSequence)).
82     */
83    @Override Hasher putUnencodedChars(CharSequence charSequence);
84  
85    /**
86     * Equivalent to {@code putBytes(charSequence.toString().getBytes(charset))}.
87     */
88    @Override Hasher putString(CharSequence charSequence, Charset charset);
89  
90    /**
91     * A simple convenience for {@code funnel.funnel(object, this)}.
92     */
93    <T> Hasher putObject(T instance, Funnel<? super T> funnel);
94  
95    /**
96     * Computes a hash code based on the data that have been provided to this hasher. The result is
97     * unspecified if this method is called more than once on the same instance.
98     */
99    HashCode hash();
100 }