dxdiskhashnodeleaf.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: DxDiskHashNodeLeaf.java,v 1.10 2000/11/09 10:43:06 daniela Exp $

package org.ozoneDB.DxLib;

import java.io.*;


/**
 * Knoten als blatt des baumes. Enthaelt keine verzweigungen aber eventuell
 * mehrere key-data-paare.
 */
public class DxDiskHashNodeLeaf extends DxDiskHashNode implements Externalizable {
    
    final static long serialVersionUID = 1;
    
    protected DxDiskHashMap grandParent;
    
    protected DxKeyData element;
    
    
    public DxDiskHashNodeLeaf( DxDiskHashMap _grandParent ) {
        grandParent = _grandParent;
    }
    
    
    public void empty() {
        element = null;
    } 
    
    
    public DxKeyData element() {
        return element;
    } 
    
    
    public boolean addForKey( Object data, Object key ) {
        //es ist noch kein element drin
        if (element == null) {
            element = grandParent.newKeyData();
            element.set( key, data );
            return true;
        } else {
            //es sind schon elemente da
            DxKeyData elem = element;
            while (elem != null) {
                if (elem.key.equals( key )) {
                    break;
                } 
                elem = elem.next;
            } 
            //key ist noch nicht drin
            if (elem == null) {
                DxKeyData newElement = grandParent.newKeyData();
                newElement.set( key, data );
                newElement.next = element;
                element = newElement;
                return true;
            } else {
                //key ist schon da :(
                return false;
            } 
        } 
    } 
    
    
    public Object elementForKey( Object key, int hashCode ) {
        DxKeyData elem = element;
        while (elem != null) {
            if (elem.key.equals( key )) {
                return elem.data;
            } 
            elem = elem.next;
        } 
        return null;
    } 
    
    
    public Object removeForKey( Object key ) {
        DxKeyData elem = element;
        while (elem != null) {
            if (elem.key.equals( key )) {
                break;
            } 
            elem = elem.next;
        } 
        
        Object answer = null;
        if (elem != null) {
            answer = elem.data;
            //daten vom ersten element der liste hier eintragen
            elem.data = element.data;
            elem.key = element.key;
            //erstes element loeschen; evtl gibt es nur noch das eine
            element = element.next;
        } 
        return answer;
    } 
    
    
    public void writeExternal( ObjectOutput out ) throws IOException {
        byte c = 0;
        for (DxKeyData elem = element; elem != null; elem = elem.next) {
            c++;
        } 
        out.writeByte( c );
        
        DxKeyData elem = element;
        while (elem != null) {
            out.writeObject( elem.key );
            out.writeObject( elem.data );
            elem = elem.next;
        } 
    } 
    
    
    public void readExternal( ObjectInput in ) throws IOException, ClassNotFoundException {
        byte c = in.readByte();
        
        element = grandParent.newKeyData();
        element.set( in.readObject(), in.readObject() );
        
        DxKeyData elem = element;
        for (int i = 1; i < c; i++) {
            elem.next = grandParent.newKeyData();
            elem.next.set( in.readObject(), in.readObject() );
            elem = elem.next;
        } 
    } 
}