将选定的文件调整为文件JFileChooser中的文件过滤器

我正在用java编写一个图表编辑器。此应用程序可以选择导出为各种标准图像格式，例如.jpg，.png等。当用户单击 File->Export 时，您将获得 一个 包含多个 s 的 for 等。JFileChooserFileFilter.jpg.png

现在这是我的问题：

有没有办法让默认的扩展名调整为选定的文件过滤器？例如，如果文档被命名为“lolcat”，那么当选择png过滤器时，默认选项应该是“lolcat.png”，当用户选择jpg文件过滤器时，默认值应该自动更改为“lolcat.jpg”。

这可能吗？我该怎么做？

编辑：根据下面的答案，我写了一些代码。但它还没有完全起作用。我已经在 中添加了一个，但似乎在此方法中返回 null。下面是代码。propertyChangeListenerFILE_FILTER_CHANGED_PROPERTYgetSelectedFile()

package nl.helixsoft;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.filechooser.FileFilter;

public class JFileChooserTest {
    public class SimpleFileFilter extends FileFilter {
        private String desc;
        private List<String> extensions;
        private boolean showDirectories;

        /**
         * @param name example: "Data files"
         * @param glob example: "*.txt|*.csv"
         */
        public SimpleFileFilter (String name, String globs) {
            extensions = new ArrayList<String>();
            for (String glob : globs.split("\\|")) {
                if (!glob.startsWith("*.")) 
                    throw new IllegalArgumentException("expected list of globs like \"*.txt|*.csv\"");
                // cut off "*"
                // store only lower case (make comparison case insensitive)
                extensions.add (glob.substring(1).toLowerCase());
            }
            desc = name + " (" + globs + ")";
        }

        public SimpleFileFilter(String name, String globs, boolean showDirectories) {
            this(name, globs);
            this.showDirectories = showDirectories;
        }

        @Override
        public boolean accept(File file) {
            if(showDirectories && file.isDirectory()) {
                return true;
            }
            String fileName = file.toString().toLowerCase();

            for (String extension : extensions) {   
                if (fileName.endsWith (extension)) {
                    return true;
                }
            }
            return false;
        }

        @Override
        public String getDescription() {
            return desc;
        }

        /**
         * @return includes '.'
         */
        public String getFirstExtension() {
            return extensions.get(0);
        }
    }

    void export() {
        String documentTitle = "lolcat";

        final JFileChooser jfc = new JFileChooser();
        jfc.setDialogTitle("Export");
        jfc.setDialogType(JFileChooser.SAVE_DIALOG);
        jfc.setSelectedFile(new File (documentTitle));
        jfc.addChoosableFileFilter(new SimpleFileFilter("JPEG", "*.jpg"));
        jfc.addChoosableFileFilter(new SimpleFileFilter("PNG", "*.png"));
        jfc.addPropertyChangeListener(JFileChooser.FILE_FILTER_CHANGED_PROPERTY, new PropertyChangeListener() {
            public void propertyChange(PropertyChangeEvent arg0) {
                System.out.println ("Property changed");
                String extold = null;
                String extnew = null;
                if (arg0.getOldValue() == null || !(arg0.getOldValue() instanceof SimpleFileFilter)) return;
                if (arg0.getNewValue() == null || !(arg0.getNewValue() instanceof SimpleFileFilter)) return;
                SimpleFileFilter oldValue = ((SimpleFileFilter)arg0.getOldValue());
                SimpleFileFilter newValue = ((SimpleFileFilter)arg0.getNewValue());
                extold = oldValue.getFirstExtension();
                extnew = newValue.getFirstExtension();
                String filename = "" + jfc.getSelectedFile();
                System.out.println ("file: " + filename + " old: " + extold + ", new: " + extnew);
                if (filename.endsWith(extold)) {
                    filename.replace(extold, extnew);
                } else {
                    filename += extnew;
                }
                jfc.setSelectedFile(new File (filename));
            }
        });
        jfc.showDialog(frame, "export");
    }

    JFrame frame;

    void run() {
        frame = new JFrame();
        JButton btn = new JButton ("export");
        frame.add (btn);
        btn.addActionListener (new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                export();
            }
        });
        frame.setSize (300, 300);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {     
            public void run() {
                JFileChooserTest x =  new JFileChooserTest();
                x.run();
            }
        });     
    }
}