353 lines
11 KiB
Java
353 lines
11 KiB
Java
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/*******************************************************************************
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* Copyright 2010 Cees De Groot, Alex Boisvert, Jan Kotek
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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******************************************************************************/
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package org.apache.jdbm;
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import java.io.*;
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import java.util.ArrayList;
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/**
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* A bucket is a placeholder for multiple (key, value) pairs. Buckets
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* are used to store collisions (same hash value) at all levels of an
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* H*tree.
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* <p/>
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* There are two types of buckets: leaf and non-leaf.
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* <p/>
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* Non-leaf buckets are buckets which hold collisions which happen
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* when the H*tree is not fully expanded. Keys in a non-leaf buckets
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* can have different hash codes. Non-leaf buckets are limited to an
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* arbitrary size. When this limit is reached, the H*tree should create
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* a new HTreeDirectory node and distribute keys of the non-leaf buckets into
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* the newly created HTreeDirectory.
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* <p/>
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* A leaf bucket is a bucket which contains keys which all have
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* the same <code>hashCode()</code>. Leaf buckets stand at the
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* bottom of an H*tree because the hashing algorithm cannot further
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* discriminate between different keys based on their hash code.
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*
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* @author Alex Boisvert
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*/
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final class HTreeBucket<K, V> {
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/**
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* The maximum number of elements (key, value) a non-leaf bucket
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* can contain.
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*/
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public static final int OVERFLOW_SIZE = 16;
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/**
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* Depth of this bucket.
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*/
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private byte _depth;
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/**
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* Keys and values in this bucket. Keys are followed by values at KEYPOS+OVERFLOW_SIZE
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*/
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private Object[] _keysAndValues;
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private byte size = 0;
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private final HTree<K, V> tree;
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/**
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* Public constructor for serialization.
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*/
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public HTreeBucket(HTree<K, V> tree) {
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this.tree = tree;
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}
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/**
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* Construct a bucket with a given depth level. Depth level is the
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* number of <code>HashDirectory</code> above this bucket.
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*/
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public HTreeBucket(HTree<K, V> tree, byte level) {
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this.tree = tree;
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if (level > HTreeDirectory.MAX_DEPTH + 1) {
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throw new IllegalArgumentException(
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"Cannot create bucket with depth > MAX_DEPTH+1. "
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+ "Depth=" + level);
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}
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_depth = level;
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_keysAndValues = new Object[OVERFLOW_SIZE * 2];
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}
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/**
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* Returns the number of elements contained in this bucket.
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*/
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public int getElementCount() {
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return size;
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}
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/**
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* Returns whether or not this bucket is a "leaf bucket".
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*/
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public boolean isLeaf() {
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return (_depth > HTreeDirectory.MAX_DEPTH);
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}
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/**
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* Returns true if bucket can accept at least one more element.
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*/
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public boolean hasRoom() {
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if (isLeaf()) {
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return true; // leaf buckets are never full
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} else {
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// non-leaf bucket
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return (size < OVERFLOW_SIZE);
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}
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}
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/**
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* Add an element (key, value) to this bucket. If an existing element
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* has the same key, it is replaced silently.
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*
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* @return Object which was previously associated with the given key
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* or <code>null</code> if no association existed.
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*/
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public V addElement(K key, V value) {
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//find entry
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byte existing = -1;
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for (byte i = 0; i < size; i++) {
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if (key.equals(_keysAndValues[i])) {
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existing = i;
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break;
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}
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}
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if (existing != -1) {
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// replace existing element
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Object before = _keysAndValues[existing + OVERFLOW_SIZE];
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if (before instanceof BTreeLazyRecord) {
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BTreeLazyRecord<V> rec = (BTreeLazyRecord<V>) before;
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before = rec.get();
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rec.delete();
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}
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_keysAndValues[existing + OVERFLOW_SIZE] = value;
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return (V) before;
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} else {
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// add new (key, value) pair
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_keysAndValues[size] = key;
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_keysAndValues[size + OVERFLOW_SIZE] = value;
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size++;
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return null;
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}
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}
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/**
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* Remove an element, given a specific key.
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*
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* @param key Key of the element to remove
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* @return Removed element value, or <code>null</code> if not found
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*/
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public V removeElement(K key) {
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//find entry
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byte existing = -1;
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for (byte i = 0; i < size; i++) {
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if (key.equals(_keysAndValues[i])) {
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existing = i;
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break;
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}
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}
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if (existing != -1) {
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Object o = _keysAndValues[existing + OVERFLOW_SIZE];
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if (o instanceof BTreeLazyRecord) {
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BTreeLazyRecord<V> rec = (BTreeLazyRecord<V>) o;
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o = rec.get();
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rec.delete();
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}
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//move last element to existing
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size--;
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_keysAndValues[existing] = _keysAndValues[size];
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_keysAndValues[existing + OVERFLOW_SIZE] = _keysAndValues[size + OVERFLOW_SIZE];
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//and unset last element
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_keysAndValues[size] = null;
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_keysAndValues[size + OVERFLOW_SIZE] = null;
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return (V) o;
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} else {
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// not found
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return null;
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}
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}
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/**
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* Returns the value associated with a given key. If the given key
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* is not found in this bucket, returns <code>null</code>.
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*/
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public V getValue(K key) {
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//find entry
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byte existing = -1;
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for (byte i = 0; i < size; i++) {
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if (key.equals(_keysAndValues[i])) {
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existing = i;
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break;
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}
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}
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if (existing != -1) {
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Object o = _keysAndValues[existing + OVERFLOW_SIZE];
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if (o instanceof BTreeLazyRecord)
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return ((BTreeLazyRecord<V>) o).get();
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else
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return (V) o;
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} else {
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// key not found
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return null;
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}
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}
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/**
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* Obtain keys contained in this buckets. Keys are ordered to match
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* their values, which be be obtained by calling <code>getValues()</code>.
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* <p/>
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* As an optimization, the Vector returned is the instance member
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* of this class. Please don't modify outside the scope of this class.
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*/
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ArrayList<K> getKeys() {
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ArrayList<K> ret = new ArrayList<K>();
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for (byte i = 0; i < size; i++) {
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ret.add((K) _keysAndValues[i]);
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}
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return ret;
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}
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/**
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* Obtain values contained in this buckets. Values are ordered to match
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* their keys, which be be obtained by calling <code>getKeys()</code>.
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* <p/>
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* As an optimization, the Vector returned is the instance member
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* of this class. Please don't modify outside the scope of this class.
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*/
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ArrayList<V> getValues() {
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ArrayList<V> ret = new ArrayList<V>();
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for (byte i = 0; i < size; i++) {
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ret.add((V) _keysAndValues[i + OVERFLOW_SIZE]);
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}
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return ret;
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}
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public void writeExternal(DataOutput out)
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throws IOException {
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out.write(_depth);
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out.write(size);
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DataInputOutput out3 = tree.writeBufferCache.getAndSet(null);
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if (out3 == null)
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out3 = new DataInputOutput();
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else
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out3.reset();
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Serializer keySerializer = tree.keySerializer != null ? tree.keySerializer : tree.getRecordManager().defaultSerializer();
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for (byte i = 0; i < size; i++) {
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out3.reset();
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keySerializer.serialize(out3, _keysAndValues[i]);
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LongPacker.packInt(out, out3.getPos());
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out.write(out3.getBuf(), 0, out3.getPos());
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}
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//write values
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if(tree.hasValues()){
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Serializer valSerializer = tree.valueSerializer != null ? tree.valueSerializer : tree.getRecordManager().defaultSerializer();
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for (byte i = 0; i < size; i++) {
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Object value = _keysAndValues[i + OVERFLOW_SIZE];
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if (value == null) {
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out.write(BTreeLazyRecord.NULL);
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} else if (value instanceof BTreeLazyRecord) {
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out.write(BTreeLazyRecord.LAZY_RECORD);
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LongPacker.packLong(out, ((BTreeLazyRecord) value).recid);
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} else {
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//transform to byte array
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out3.reset();
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valSerializer.serialize(out3, value);
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if (out3.getPos() > BTreeLazyRecord.MAX_INTREE_RECORD_SIZE) {
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//store as separate record
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long recid = tree.getRecordManager().insert(out3.toByteArray(), BTreeLazyRecord.FAKE_SERIALIZER,true);
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out.write(BTreeLazyRecord.LAZY_RECORD);
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LongPacker.packLong(out, recid);
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} else {
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out.write(out3.getPos());
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out.write(out3.getBuf(), 0, out3.getPos());
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}
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}
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}
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}
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tree.writeBufferCache.set(out3);
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}
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public void readExternal(DataInputOutput in) throws IOException, ClassNotFoundException {
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_depth = in.readByte();
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size = in.readByte();
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//read keys
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Serializer keySerializer = tree.keySerializer != null ? tree.keySerializer : tree.getRecordManager().defaultSerializer();
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_keysAndValues = (K[]) new Object[OVERFLOW_SIZE * 2];
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for (byte i = 0; i < size; i++) {
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int expectedSize = LongPacker.unpackInt(in);
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K key = (K) BTreeLazyRecord.fastDeser(in, keySerializer, expectedSize);
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_keysAndValues[i] = key;
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}
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//read values
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if(tree.hasValues()){
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Serializer<V> valSerializer = tree.valueSerializer != null ? tree.valueSerializer : (Serializer<V>) tree.getRecordManager().defaultSerializer();
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for (byte i = 0; i < size; i++) {
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int header = in.readUnsignedByte();
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if (header == BTreeLazyRecord.NULL) {
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_keysAndValues[i + OVERFLOW_SIZE] = null;
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} else if (header == BTreeLazyRecord.LAZY_RECORD) {
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long recid = LongPacker.unpackLong(in);
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_keysAndValues[i + OVERFLOW_SIZE] = (new BTreeLazyRecord(tree.getRecordManager(), recid, valSerializer));
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} else {
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_keysAndValues[i + OVERFLOW_SIZE] = BTreeLazyRecord.fastDeser(in, valSerializer, header);
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}
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}
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}else{
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for (byte i = 0; i < size; i++) {
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if(_keysAndValues[i]!=null)
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_keysAndValues[i+OVERFLOW_SIZE] = Utils.EMPTY_STRING;
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}
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}
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}
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}
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