com.google.common.hash.HashCodes.java Source code

Introduction

Here is the source code for com.google.common.hash.HashCodes.java

Source

/*
 * 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 static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.Beta;
import com.google.common.primitives.UnsignedInts;

import java.io.Serializable;

/**
 * Static factories for creating {@link HashCode} instances; most users should never have to use
 * this. All returned instances are {@link Serializable}.
 *
 * @author Dimitris Andreou
 * @since 12.0
 */
@Beta
public final class HashCodes {
    private HashCodes() {
    }

    /**
     * Creates a 32-bit {@code HashCode}, of which the bytes will form the passed int, interpreted 
     * in little endian order.
     */
    public static HashCode fromInt(int hash) {
        return new IntHashCode(hash);
    }

    private static final class IntHashCode extends HashCode implements Serializable {
        final int hash;

        IntHashCode(int hash) {
            this.hash = hash;
        }

        @Override
        public int bits() {
            return 32;
        }

        @Override
        public byte[] asBytes() {
            return new byte[] { (byte) hash, (byte) (hash >> 8), (byte) (hash >> 16), (byte) (hash >> 24) };
        }

        @Override
        public int asInt() {
            return hash;
        }

        @Override
        public long asLong() {
            throw new IllegalStateException("this HashCode only has 32 bits; cannot create a long");
        }

        @Override
        public long padToLong() {
            return UnsignedInts.toLong(hash);
        }

        private static final long serialVersionUID = 0;
    }

    /**
     * Creates a 64-bit {@code HashCode}, of which the bytes will form the passed long, interpreted 
     * in little endian order.
     */
    public static HashCode fromLong(long hash) {
        return new LongHashCode(hash);
    }

    private static final class LongHashCode extends HashCode implements Serializable {
        final long hash;

        LongHashCode(long hash) {
            this.hash = hash;
        }

        @Override
        public int bits() {
            return 64;
        }

        @Override
        public byte[] asBytes() {
            return new byte[] { (byte) hash, (byte) (hash >> 8), (byte) (hash >> 16), (byte) (hash >> 24),
                    (byte) (hash >> 32), (byte) (hash >> 40), (byte) (hash >> 48), (byte) (hash >> 56) };
        }

        @Override
        public int asInt() {
            return (int) hash;
        }

        @Override
        public long asLong() {
            return hash;
        }

        @Override
        public long padToLong() {
            return hash;
        }

        private static final long serialVersionUID = 0;
    }

    /**
     * Creates a {@code HashCode} from a byte array. The array is defensively copied to preserve
     * the immutability contract of {@code HashCode}. The array cannot be empty.
     */
    public static HashCode fromBytes(byte[] bytes) {
        checkArgument(bytes.length >= 1, "A HashCode must contain at least 1 byte.");
        return fromBytesNoCopy(bytes.clone());
    }

    /**
     * Creates a {@code HashCode} from a byte array. The array is <i>not</i> copied defensively, 
     * so it must be handed-off so as to preserve the immutability contract of {@code HashCode}.
     */
    static HashCode fromBytesNoCopy(byte[] bytes) {
        return new BytesHashCode(bytes);
    }

    private static final class BytesHashCode extends HashCode implements Serializable {
        final byte[] bytes;

        BytesHashCode(byte[] bytes) {
            this.bytes = checkNotNull(bytes);
        }

        @Override
        public int bits() {
            return bytes.length * 8;
        }

        @Override
        public byte[] asBytes() {
            return bytes.clone();
        }

        @Override
        public int asInt() {
            checkState(bytes.length >= 4, "HashCode#asInt() requires >= 4 bytes (it only has %s bytes).",
                    bytes.length);
            return (bytes[0] & 0xFF) | ((bytes[1] & 0xFF) << 8) | ((bytes[2] & 0xFF) << 16)
                    | ((bytes[3] & 0xFF) << 24);
        }

        @Override
        public long asLong() {
            checkState(bytes.length >= 8, "HashCode#asLong() requires >= 8 bytes (it only has %s bytes).",
                    bytes.length);
            return (bytes[0] & 0xFFL) | ((bytes[1] & 0xFFL) << 8) | ((bytes[2] & 0xFFL) << 16)
                    | ((bytes[3] & 0xFFL) << 24) | ((bytes[4] & 0xFFL) << 32) | ((bytes[5] & 0xFFL) << 40)
                    | ((bytes[6] & 0xFFL) << 48) | ((bytes[7] & 0xFFL) << 56);
        }

        @Override
        public long padToLong() {
            return (bytes.length < 8) ? UnsignedInts.toLong(asInt()) : asLong();
        }

        @Override
        public int hashCode() {
            if (bytes.length >= 4) {
                return asInt();
            } else {
                int val = (bytes[0] & 0xFF);
                for (int i = 1; i < bytes.length; i++) {
                    val |= ((bytes[i] & 0xFF) << (i * 8));
                }
                return val;
            }
        }

        private static final long serialVersionUID = 0;
    }
}