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; 021import org.checkerframework.checker.nullness.qual.Nullable; 022 023/** 024 * A {@link PrimitiveSink} that can compute a hash code after reading the input. Each hasher should 025 * translate all multibyte values ({@link #putInt(int)}, {@link #putLong(long)}, etc) to bytes in 026 * little-endian order. 027 * 028 * <p><b>Warning:</b> The result of calling any methods after calling {@link #hash} is undefined. 029 * 030 * <p><b>Warning:</b> Using a specific character encoding when hashing a {@link CharSequence} with 031 * {@link #putString(CharSequence, Charset)} is generally only useful for cross-language 032 * compatibility (otherwise prefer {@link #putUnencodedChars}). However, the character encodings 033 * must be identical across languages. Also beware that {@link Charset} definitions may occasionally 034 * change between Java releases. 035 * 036 * <p><b>Warning:</b> Chunks of data that are put into the {@link Hasher} are not delimited. The 037 * resulting {@link HashCode} is dependent only on the bytes inserted, and the order in which they 038 * were inserted, not how those bytes were chunked into discrete put() operations. For example, the 039 * following three expressions all generate colliding hash codes: 040 * 041 * <pre>{@code 042 * newHasher().putByte(b1).putByte(b2).putByte(b3).hash() 043 * newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash() 044 * newHasher().putBytes(new byte[] { b1, b2, b3 }).hash() 045 * }</pre> 046 * 047 * <p>If you wish to avoid this, you should either prepend or append the size of each chunk. Keep in 048 * mind that when dealing with char sequences, the encoded form of two concatenated char sequences 049 * is not equivalent to the concatenation of their encoded form. Therefore, {@link 050 * #putString(CharSequence, Charset)} should only be used consistently with <i>complete</i> 051 * sequences and not broken into chunks. 052 * 053 * @author Kevin Bourrillion 054 * @since 11.0 055 */ 056@Beta 057@CanIgnoreReturnValue 058@ElementTypesAreNonnullByDefault 059public interface Hasher extends PrimitiveSink { 060 @Override 061 Hasher putByte(byte b); 062 063 @Override 064 Hasher putBytes(byte[] bytes); 065 066 @Override 067 Hasher putBytes(byte[] bytes, int off, int len); 068 069 @Override 070 Hasher putBytes(ByteBuffer bytes); 071 072 @Override 073 Hasher putShort(short s); 074 075 @Override 076 Hasher putInt(int i); 077 078 @Override 079 Hasher putLong(long l); 080 081 /** Equivalent to {@code putInt(Float.floatToRawIntBits(f))}. */ 082 @Override 083 Hasher putFloat(float f); 084 085 /** Equivalent to {@code putLong(Double.doubleToRawLongBits(d))}. */ 086 @Override 087 Hasher putDouble(double d); 088 089 /** Equivalent to {@code putByte(b ? (byte) 1 : (byte) 0)}. */ 090 @Override 091 Hasher putBoolean(boolean b); 092 093 @Override 094 Hasher putChar(char c); 095 096 /** 097 * Equivalent to processing each {@code char} value in the {@code CharSequence}, in order. In 098 * other words, no character encoding is performed; the low byte and high byte of each {@code 099 * char} are hashed directly (in that order). The input must not be updated while this method is 100 * in progress. 101 * 102 * <p><b>Warning:</b> This method will produce different output than most other languages do when 103 * running the same hash function on the equivalent input. For cross-language compatibility, use 104 * {@link #putString}, usually with a charset of UTF-8. For other use cases, use {@code 105 * putUnencodedChars}. 106 * 107 * @since 15.0 (since 11.0 as putString(CharSequence)). 108 */ 109 @Override 110 Hasher putUnencodedChars(CharSequence charSequence); 111 112 /** 113 * Equivalent to {@code putBytes(charSequence.toString().getBytes(charset))}. 114 * 115 * <p><b>Warning:</b> This method, which reencodes the input before hashing it, is useful only for 116 * cross-language compatibility. For other use cases, prefer {@link #putUnencodedChars}, which is 117 * faster, produces the same output across Java releases, and hashes every {@code char} in the 118 * input, even if some are invalid. 119 */ 120 @Override 121 Hasher putString(CharSequence charSequence, Charset charset); 122 123 /** A simple convenience for {@code funnel.funnel(object, this)}. */ 124 <T extends @Nullable Object> Hasher putObject( 125 @ParametricNullness T instance, Funnel<? super T> funnel); 126 127 /** 128 * Computes a hash code based on the data that have been provided to this hasher. The result is 129 * unspecified if this method is called more than once on the same instance. 130 */ 131 HashCode hash(); 132 133 /** 134 * {@inheritDoc} 135 * 136 * @deprecated This returns {@link Object#hashCode()}; you almost certainly mean to call {@code 137 * hash().asInt()}. 138 */ 139 @Override 140 @Deprecated 141 int hashCode(); 142}