Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 org.apache.lucene.util; /** Represents byte[], as a slice (offset + length) into an * existing byte[]. The {@link #bytes} member should never be null; * use {@link #EMPTY_BYTES} if necessary. * * <p><b>Important note:</b> Unless otherwise noted, Lucene uses this class to * represent terms that are encoded as <b>UTF8</b> bytes in the index. To * convert them to a Java {@link String} (which is UTF16), use {@link #utf8ToString}. * Using code like {@code new String(bytes, offset, length)} to do this * is <b>wrong</b>, as it does not respect the correct character set * and may return wrong results (depending on the platform's defaults)! * * <p>{@code BytesRef} implements {@link Comparable}. The underlying byte arrays * are sorted lexicographically, numerically treating elements as unsigned. * This is identical to Unicode codepoint order. */ public final class BytesRef implements Comparable<BytesRef>, Cloneable { /** An empty byte array for convenience */ public static final byte[] EMPTY_BYTES = new byte[0]; /** The contents of the BytesRef. Should never be {@code null}. */ public byte[] bytes; /** Offset of first valid byte. */ public int offset; /** Length of used bytes. */ public int length; /** Create a BytesRef with {@link #EMPTY_BYTES} */ public BytesRef() { this(EMPTY_BYTES); } /** This instance will directly reference bytes w/o making a copy. * bytes should not be null. */ public BytesRef(byte[] bytes, int offset, int length) { this.bytes = bytes; this.offset = offset; this.length = length; assert isValid(); } /** This instance will directly reference bytes w/o making a copy. * bytes should not be null */ public BytesRef(byte[] bytes) { this(bytes, 0, bytes.length); } /** * Create a BytesRef pointing to a new array of size <code>capacity</code>. * Offset and length will both be zero. */ public BytesRef(int capacity) { this.bytes = new byte[capacity]; } /** * Initialize the byte[] from the UTF8 bytes * for the provided String. * * @param text This must be well-formed * unicode text, with no unpaired surrogates. */ public BytesRef(CharSequence text) { this(new byte[UnicodeUtil.maxUTF8Length(text.length())]); length = UnicodeUtil.UTF16toUTF8(text, 0, text.length(), bytes); } /** * Expert: compares the bytes against another BytesRef, * returning true if the bytes are equal. * * @param other Another BytesRef, should not be null. * @lucene.internal */ public boolean bytesEquals(BytesRef other) { return FutureArrays.equals(this.bytes, this.offset, this.offset + this.length, other.bytes, other.offset, other.offset + other.length); } /** * Returns a shallow clone of this instance (the underlying bytes are * <b>not</b> copied and will be shared by both the returned object and this * object. * * @see #deepCopyOf */ @Override public BytesRef clone() { return new BytesRef(bytes, offset, length); } /** Calculates the hash code as required by TermsHash during indexing. * <p> This is currently implemented as MurmurHash3 (32 * bit), using the seed from {@link * StringHelper#GOOD_FAST_HASH_SEED}, but is subject to * change from release to release. */ @Override public int hashCode() { return StringHelper.murmurhash3_x86_32(this, StringHelper.GOOD_FAST_HASH_SEED); } @Override public boolean equals(Object other) { if (other == null) { return false; } if (other instanceof BytesRef) { return this.bytesEquals((BytesRef) other); } return false; } /** Interprets stored bytes as UTF8 bytes, returning the * resulting string */ public String utf8ToString() { final char[] ref = new char[length]; final int len = UnicodeUtil.UTF8toUTF16(bytes, offset, length, ref); return new String(ref, 0, len); } /** Returns hex encoded bytes, eg [0x6c 0x75 0x63 0x65 0x6e 0x65] */ @Override public String toString() { StringBuilder sb = new StringBuilder(); sb.append('['); final int end = offset + length; for (int i = offset; i < end; i++) { if (i > offset) { sb.append(' '); } sb.append(Integer.toHexString(bytes[i] & 0xff)); } sb.append(']'); return sb.toString(); } /** Unsigned byte order comparison */ @Override public int compareTo(BytesRef other) { return FutureArrays.compareUnsigned(this.bytes, this.offset, this.offset + this.length, other.bytes, other.offset, other.offset + other.length); } /** * Creates a new BytesRef that points to a copy of the bytes from * <code>other</code> * <p> * The returned BytesRef will have a length of other.length * and an offset of zero. */ public static BytesRef deepCopyOf(BytesRef other) { return new BytesRef(ArrayUtil.copyOfSubArray(other.bytes, other.offset, other.offset + other.length), 0, other.length); } /** * Performs internal consistency checks. * Always returns true (or throws IllegalStateException) */ public boolean isValid() { if (bytes == null) { throw new IllegalStateException("bytes is null"); } if (length < 0) { throw new IllegalStateException("length is negative: " + length); } if (length > bytes.length) { throw new IllegalStateException("length is out of bounds: " + length + ",bytes.length=" + bytes.length); } if (offset < 0) { throw new IllegalStateException("offset is negative: " + offset); } if (offset > bytes.length) { throw new IllegalStateException("offset out of bounds: " + offset + ",bytes.length=" + bytes.length); } if (offset + length < 0) { throw new IllegalStateException("offset+length is negative: offset=" + offset + ",length=" + length); } if (offset + length > bytes.length) { throw new IllegalStateException("offset+length out of bounds: offset=" + offset + ",length=" + length + ",bytes.length=" + bytes.length); } return true; } }