如何使用JFilechooser检查文件是否已保存？

Question

我一直在编写文本编辑器，我创建了一个菜单，可以保存文件。我能够编写保存文件所需的代码，但是如何检查该特定文件是否已保存？如果已保存，则只保存对该文件的任何更改，但如果尚未保存，请使用新名称保存该文件。任何帮助都将非常感谢，因为我已经阅读了java api以及已经发布在此处的类似问题，似乎对我没有任何帮助。这就是我所拥有的：

            JFileChooser saveAsChooser = new JFileChooser();
            saveAsItem.addActionListener(event -> {
            int saveResult = saveAsChooser.showSaveDialog(this);
            File myFile = saveAsChooser.getSelectedFile();
            String fileName = myFile.getName().toString();
            setMyTitle("Swing Text Editor [" + fileName + "]");

            if(saveResult == JFileChooser.APPROVE_OPTION)
            {
                try {
                PrintWriter file = new PrintWriter(new File(myFile.getName()));
                file.close();
                } catch (IOException e) {
                        e.printStackTrace();
                }
            }
    });


    JFileChooser saveChooser = new JFileChooser();
    saveItem.addActionListener(event -> {
        int saveResult = saveChooser.showSaveDialog(this);
        File myFile = saveAsChooser.getSelectedFile();
        File myFileName = new File(myFile.getName());
        String fileName = myFile.getName().toString();
        setMyTitle("Swing Text Editor [" + fileName + "]");

        if(saveResult == JFileChooser.APPROVE_OPTION)
        {
            if(myFileName.exists() == false)
            {
                try {
                PrintWriter file = new PrintWriter(new File(myFile.getName()));
                file.close();
                } catch (IOException e) {
                        e.printStackTrace();
                }
            }
        }
        else if(saveResult == JFileChooser.APPROVE_OPTION)
        {
            if(myFileName.exists() == true)
            {
                try {
                PrintWriter file = new PrintWriter(myFile.getName());
                } catch (IOException e) {
                        e.printStackTrace();
                }
            }
        }
    });

这就是崩溃时所说的内容：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at MyFrame.lambda$new$3(Editor.java:146)
    at     javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
    at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:833)
    at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:877)
    at java.awt.Component.processMouseEvent(Component.java:6533)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6298)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)