deathobjectbuffer.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 Core 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: DeathObjectBuffer.java,v 1.5 2000/10/28 16:55:17 daniela Exp $

package org.ozoneDB.core.classicStore;

import org.ozoneDB.core.*;
import org.ozoneDB.util.*;
import org.ozoneDB.DxLib.*;


public class DeathObjectBuffer extends Object {
    
    /** all objects ordered by their ObjectID */
    public DxMap objects;
    
    /** head and tail of the double linked list */
    DeathObject head;
    DeathObject tail;
    
    int bufferSize = 0;
    
    
    /** the constructor */
    public DeathObjectBuffer() {
        objects = new DxHashMap();
        head = new DeathObject();
        tail = new DeathObject();
        head.previous = tail;
        tail.next = head;
    }
    
    
    /** returns the current size of the buffer */
    public final int size() {
        return bufferSize;
    } 
    
    
    /** returns the current count of objects of the buffer */
    public final int count() {
        return objects.count();
    } 
    
    
    /**
     */
    public void updateSize( DeathObject obj, boolean sub ) {
        bufferSize += sub ? -obj.size() : obj.size();
    } 
    
    
    /**
     * adds the object to the bottom of the stack
     */
    public boolean add( DeathObject obj ) {
        boolean result = objects.addForKey( obj, obj.objID() );
        if (result) {
            popOnTop( obj );
            bufferSize += obj.size();
        } 
        return result;
    } 
    
    
    /**
     * removes the object from the stack
     */
    public DeathObject remove( ObjectID oid ) {
        //env.logWriter.newEntry ("DeathObjectBuffer.remove: " + oid, LogWriter.DEBUG3);
        DeathObject obj = (DeathObject)objects.removeForKey( oid );
        if (obj != null) {
            removeFromStack( obj );
            bufferSize -= obj.size();
        } 
        return obj;
    } 
    
    
    /**
     * moves the specified object to the top of the stack
     */
    public boolean moveToTop( ObjectID oid ) {
        DeathObject obj = (DeathObject)objects.elementForKey( oid );
        if (obj != null) {
            removeFromStack( obj );
            popOnTop( obj );
        } 
        return obj != null;
    } 
    
    
    /**
     * removes and returns the object at the bottom
     */
    public DeathObject pushFromBottom() {
        DeathObject obj = tail.next;
        if (obj == head) {
            return null;
        } 
        return remove( obj.objID() );
    } 
    
    
    /**
     * returns the DeathObject for the specified ObjectID
     */
    public DeathObject objectForId( ObjectID oid ) {
        return (DeathObject)objects.elementForKey( oid );
    } 
    
    
    /**
     * pops the object on the top of the stack
     */
    private void popOnTop( DeathObject obj ) {
        head.previous.next = obj;
        obj.previous = head.previous;
        obj.next = head;
        head.previous = obj;
    } 
    
    
    /**
     * pops the object on the bottom of the stack
     */
    private void popOnBottom( DeathObject obj ) {
        tail.next.previous = obj;
        obj.next = tail.next;
        obj.previous = tail;
        tail.next = obj;
    } 
    
    
    /**
     * removes the object from the stack
     */
    private void removeFromStack( DeathObject obj ) {
        obj.previous.next = obj.next;
        obj.next.previous = obj.previous;
    } 
}