scrollable.java

java 数据库 功能强大 效率高 SmallSQL Database is a free DBMS library for the Java(tm) platform. It runs on

/* =============================================================
 * SmallSQL : a free Java DBMS library for the Java(tm) platform
 * =============================================================
 *
 * (C) Copyright 2004-2007, by Volker Berlin.
 *
 * Project Info:  http://www.smallsql.de/
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------
 * Scrollable.java
 * ---------------
 * Author: Volker Berlin
 * 
 * Created on 05.07.2004
 */
package smallsql.database;

/**
 * Scrollable is a RowSource wrapper to add the feature of scrollable to any RowSource.
 * @author Volker Berlin
 */
class Scrollable extends RowSource {

	/** The internal not scrollable RowSource */
	private final RowSource rowSource;
	
	/** The current row number */
	private int rowIdx;
		
	/** A map of row number to the RowPositions of the internal RowSource */ 
	private final LongList rowList = new LongList();
	
	/** Detect if on any previous scrolling the last row was reached. */
	//private boolean lastIsFound;
	

	Scrollable(RowSource rowSource){
		this.rowSource = rowSource;
	}
	
	
	final boolean isScrollable(){
		return true;
	}
	
	
	void beforeFirst() throws Exception {
		rowIdx = -1;
		rowSource.beforeFirst();
	}


	boolean isBeforeFirst(){
		return rowIdx == -1 || rowList.size() == 0;
	}


	boolean isFirst(){
		return rowIdx == 0 && rowList.size()>0;
	}
	
	
	boolean first() throws Exception {
		rowIdx = -1;
		return next();
	}


	boolean previous() throws Exception{
		if(rowIdx > -1){
			rowIdx--;
			if(rowIdx > -1 && rowIdx < rowList.size()){
				rowSource.setRowPosition( rowList.get(rowIdx) );
				return true;
			}
		}
		rowSource.beforeFirst();
		return false;
	}
	
	
	boolean next() throws Exception {
		if(++rowIdx < rowList.size()){
			rowSource.setRowPosition( rowList.get(rowIdx) );
			return true;
		}
		final boolean result = rowSource.next();
		if(result){
			rowList.add( rowSource.getRowPosition());
			return true;
		}
        rowIdx = rowList.size(); //rowIdx should be never larger as row count
		return false;
	}


	boolean last() throws Exception{
		afterLast();
		return previous();
	}
	
	
	boolean isLast() throws Exception{
        if(rowIdx+1 != rowList.size()){
            // there are more rows after the current row (rowIdx+1 < rowList.size())
            // or we are after the last row (rowIdx+1 > rowList.size())
            return false; 
        }
		boolean isNext = next();
        previous();
        return !isNext && (rowIdx+1 == rowList.size() && rowList.size()>0);
	}

	boolean isAfterLast() throws Exception{
		if(rowIdx >= rowList.size()) return true;
        if(isBeforeFirst() && rowList.size() == 0){
            next();
            previous();
            if(rowList.size() == 0) return true;
        }
        return false;
	}
    

	void afterLast() throws Exception {
		if(rowIdx+1 < rowList.size()){
			rowIdx = rowList.size()-1;
			rowSource.setRowPosition( rowList.get(rowIdx) );
		}
		while(next()){/* scroll after the end */}
	}


	boolean absolute(int row) throws Exception{
		if(row == 0)
			throw Utils.createSQLException("The call absolute(0) is invalid.");
		if(row < 0){
			afterLast();
			rowIdx = rowList.size() + row;
			if(rowIdx < 0){
				beforeFirst();
				return false;
			}else{
				rowSource.setRowPosition( rowList.get(rowIdx) );
				return true;
			}
		}
		if(row <= rowList.size()){
			rowIdx = row-1;
			rowSource.setRowPosition( rowList.get(rowIdx) );
			return true;
		}
		
		rowIdx = rowList.size()-1;
		if(rowIdx >= 0)
			rowSource.setRowPosition( rowList.get(rowIdx) );
		boolean result;
		while((result = next()) && row-1 > rowIdx){/* scroll forward */}
		return result;
	}
	
	
	boolean relative(int rows) throws Exception{
		int newRow = rows + rowIdx + 1;
		if(newRow <= 0){
			beforeFirst();
			return false;
		}else{
			return absolute(newRow);
		}
	}
	
	
	int getRow() throws Exception {
        if(rowIdx >= rowList.size()) return 0;
		return rowIdx + 1;
	}


	long getRowPosition() {
		return rowIdx;
	}


	void setRowPosition(long rowPosition) throws Exception {
		rowIdx = (int)rowPosition;
	}


	final boolean rowInserted(){
		return rowSource.rowInserted();
	}
	
	
	final boolean rowDeleted(){
		return rowSource.rowDeleted();
	}
	
	
	void nullRow() {
		rowSource.nullRow();
		rowIdx = -1;
	}


	void noRow() {
		rowSource.noRow();
		rowIdx = -1;
	}

	
	void execute() throws Exception{
		rowSource.execute();
		rowList.clear();
		rowIdx = -1;
	}
}