001/* 002 * Copyright (C) 2011 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.hash; 016 017import com.google.common.annotations.Beta; 018import com.google.errorprone.annotations.CanIgnoreReturnValue; 019import java.nio.ByteBuffer; 020import java.nio.charset.Charset; 021 022/** 023 * A {@link PrimitiveSink} that can compute a hash code after reading the input. Each hasher should 024 * translate all multibyte values ({@link #putInt(int)}, {@link #putLong(long)}, etc) to bytes in 025 * little-endian order. 026 * 027 * <p><b>Warning:</b> The result of calling any methods after calling {@link #hash} is undefined. 028 * 029 * <p><b>Warning:</b> Using a specific character encoding when hashing a {@link CharSequence} with 030 * {@link #putString(CharSequence, Charset)} is generally only useful for cross-language 031 * compatibility (otherwise prefer {@link #putUnencodedChars}). However, the character encodings 032 * must be identical across languages. Also beware that {@link Charset} definitions may occasionally 033 * change between Java releases. 034 * 035 * <p><b>Warning:</b> Chunks of data that are put into the {@link Hasher} are not delimited. The 036 * resulting {@link HashCode} is dependent only on the bytes inserted, and the order in which they 037 * were inserted, not how those bytes were chunked into discrete put() operations. For example, the 038 * following three expressions all generate colliding hash codes: 039 * 040 * <pre>{@code 041 * newHasher().putByte(b1).putByte(b2).putByte(b3).hash() 042 * newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash() 043 * newHasher().putBytes(new byte[] { b1, b2, b3 }).hash() 044 * }</pre> 045 * 046 * <p>If you wish to avoid this, you should either prepend or append the size of each chunk. Keep in 047 * mind that when dealing with char sequences, the encoded form of two concatenated char sequences 048 * is not equivalent to the concatenation of their encoded form. Therefore, {@link 049 * #putString(CharSequence, Charset)} should only be used consistently with <i>complete</i> 050 * sequences and not broken into chunks. 051 * 052 * @author Kevin Bourrillion 053 * @since 11.0 054 */ 055@Beta 056@CanIgnoreReturnValue 057public interface Hasher extends PrimitiveSink { 058 @Override 059 Hasher putByte(byte b); 060 061 @Override 062 Hasher putBytes(byte[] bytes); 063 064 @Override 065 Hasher putBytes(byte[] bytes, int off, int len); 066 067 @Override 068 Hasher putBytes(ByteBuffer bytes); 069 070 @Override 071 Hasher putShort(short s); 072 073 @Override 074 Hasher putInt(int i); 075 076 @Override 077 Hasher putLong(long l); 078 079 /** Equivalent to {@code putInt(Float.floatToRawIntBits(f))}. */ 080 @Override 081 Hasher putFloat(float f); 082 083 /** Equivalent to {@code putLong(Double.doubleToRawLongBits(d))}. */ 084 @Override 085 Hasher putDouble(double d); 086 087 /** Equivalent to {@code putByte(b ? (byte) 1 : (byte) 0)}. */ 088 @Override 089 Hasher putBoolean(boolean b); 090 091 @Override 092 Hasher putChar(char c); 093 094 /** 095 * Equivalent to processing each {@code char} value in the {@code CharSequence}, in order. In 096 * other words, no character encoding is performed; the low byte and high byte of each {@code 097 * char} are hashed directly (in that order). The input must not be updated while this method is 098 * in progress. 099 * 100 * <p><b>Warning:</b> This method will produce different output than most other languages do when 101 * running the same hash function on the equivalent input. For cross-language compatibility, use 102 * {@link #putString}, usually with a charset of UTF-8. For other use cases, use {@code 103 * putUnencodedChars}. 104 * 105 * @since 15.0 (since 11.0 as putString(CharSequence)). 106 */ 107 @Override 108 Hasher putUnencodedChars(CharSequence charSequence); 109 110 /** 111 * Equivalent to {@code putBytes(charSequence.toString().getBytes(charset))}. 112 * 113 * <p><b>Warning:</b> This method, which reencodes the input before hashing it, is useful only for 114 * cross-language compatibility. For other use cases, prefer {@link #putUnencodedChars}, which is 115 * faster, produces the same output across Java releases, and hashes every {@code char} in the 116 * input, even if some are invalid. 117 */ 118 @Override 119 Hasher putString(CharSequence charSequence, Charset charset); 120 121 /** A simple convenience for {@code funnel.funnel(object, this)}. */ 122 <T> Hasher putObject(T instance, Funnel<? super T> funnel); 123 124 /** 125 * Computes a hash code based on the data that have been provided to this hasher. The result is 126 * unspecified if this method is called more than once on the same instance. 127 */ 128 HashCode hash(); 129 130 /** 131 * {@inheritDoc} 132 * 133 * @deprecated This returns {@link Object#hashCode()}; you almost certainly mean to call {@code 134 * hash().asInt()}. 135 */ 136 @Override 137 @Deprecated 138 int hashCode(); 139}