source: josm/src/org/openstreetmap/josm/actions/DiskAccessAction.java@ 78

package org.openstreetmap.josm.actions;

import java.io.File;

import javax.swing.JFileChooser;
import javax.swing.JOptionPane;
import javax.swing.KeyStroke;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.osm.OsmPrimitive;

/**
 * Helper class for all actions, that access the disk
 */
abstract public class DiskAccessAction extends JosmAction {

        public DiskAccessAction(String name, String iconName, String tooltip, String shortCutName, KeyStroke shortCut) {
                super(name, iconName, tooltip, shortCutName, shortCut);
        }
        
        
        /**
         * Check the data set if it would be empty on save. It is empty, if it contains
         * no objects (after all objects that are created and deleted without beeing 
         * transfered to the server have been removed).
         *  
         * @return <code>true</code>, if a save result in an empty data set.
         */
        protected boolean isDataSetEmpty() {
                for (OsmPrimitive osm : Main.main.ds.allNonDeletedPrimitives())
                        if (osm.id > 0)
                                return false;
                return true;
        }
        
        protected JFileChooser createAndOpenFileChooser(boolean open, boolean multiple) {
                String curDir = Main.pref.get("lastDirectory");
                if (curDir.equals(""))
                        curDir = ".";
                JFileChooser fc = new JFileChooser(new File(curDir));
                fc.setMultiSelectionEnabled(multiple);
                for (int i = 0; i < ExtensionFileFilter.filters.length; ++i)
                        fc.addChoosableFileFilter(ExtensionFileFilter.filters[i]);
                fc.setAcceptAllFileFilterUsed(true);
        
                int answer = open ? fc.showOpenDialog(Main.main) : fc.showSaveDialog(Main.main);
                if (answer != JFileChooser.APPROVE_OPTION)
                        return null;
                
                if (!fc.getCurrentDirectory().getAbsolutePath().equals(curDir))
                        Main.pref.put("lastDirectory", fc.getCurrentDirectory().getAbsolutePath());

                if (!open) {
                        File file = fc.getSelectedFile();
                        if (file == null || (file.exists() && JOptionPane.YES_OPTION != 
                                        JOptionPane.showConfirmDialog(Main.main, "File exists. Overwrite?", "Overwrite", JOptionPane.YES_NO_OPTION)))
                                return null;
                }
                
                return fc;
        }}