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 }