dxbbtree.java

用Java写的面相对象的数据库管理系统

// You can redistribute this software and/or modify it under the terms of
// the Ozone Library License version 1 published by ozone-db.org.
//
// The original code and portions created by SMB are
// Copyright (C) 1997-2000 by SMB GmbH. All rights reserved.
//
// $Id: DxBBTree.java,v 1.6 2000/10/28 16:55:14 daniela Exp $

package org.ozoneDB.DxLib;

import java.io.*;


/**
 * Non-public class that represents a key->value map implemented
 * using a BBTree. This is used for DxTreeMap and DxTreeSet implementations.
 */
final class DxBBTree {
    
    final static long serialVersionUID = 1L;
    
    //balance faktor fuer den baum (0.25..0.32); je kleiner, desto
    //schiefer ist evtl. der baum und umso weniger muss auch rotiert werden
    final static int BB_ALPHA = 26;
    final static int BB_BALANCE = 50;
    final static int BB_MAX = 100;
    
    DxBBnode quietRoot;
    int itemCount = 0;
    DxComparator comparator = null;
    
    
    /**
     */
    public DxBBTree() {
        comparator = new DxStandardComparator();
        quietRoot = new DxBBnode( null, null, comparator );
    }
    
    
    /**
     */
    public DxBBTree( DxComparator _comparator ) {
        comparator = _comparator;
        quietRoot = new DxBBnode( null, null, comparator );
    }
    
    
    /**
     */
    public synchronized boolean addForKey( Object obj, Object key ) {
        DxBBnode node = new DxBBnode( obj, key, comparator );
        if (itemCount == 0) {
            node.isRight = true;
            node.pa = quietRoot;
            quietRoot.re = node;
            itemCount++;
            return true;
        } 
        if (root().insertNode( node )) {
            itemCount++;
            return true;
        } else {
            return false;
        } 
    } 
    
    
    /**
     */
    public Object elementForKey( Object key ) {
        if (root() == null) {
            return null;
        } 
        
        DxBBnode node = root().findNodeKey( key );
        if (node != null) {
            return node.data;
        } 
        
        return null;
    } 
    
    
    /**
     */
    public Object keyForElement( Object obj ) {
        if (root() == null) {
            return null;
        } 
        
        DxBBnode node = root().findNodeObject( obj );
        if (node != null) {
            return node.key;
        } 
        
        return null;
    } 
    
    
    /**
     */
    public synchronized Object removeForKey( Object key ) {
        if (root() == null) {
            return null;
        } 
        
        DxBBnode node = root().removeNodeKey( key );
        if (node != null) {
            itemCount--;
            return node.data;
        } else {
            return null;
        } 
    } 
    
    
    /**
     */
    public int count() {
        return itemCount;
    } 
    
    
    /**
     */
    public boolean isEmpty() {
        return itemCount == 0;
    } 
    
    
    /**
     */
    public boolean containsKey( Object key ) {
        return elementForKey( key ) != null;
    } 
    
    
    /**
     */
    DxBBnode root() {
        return quietRoot.re;
    } 
}