在我的代码中，我有这个代码
void selectRoot() {
JFileChooser ch = new JFileChooser();
ch.showOpenDialog((JFrame)this);
}
抛出该异常:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.io.Win32FileSystem.normalize(Win32FileSystem.java:164)
at java.io.Win32FileSystem.getUserPath(Win32FileSystem.java:296)
at java.io.Win32FileSystem.resolve(Win32FileSystem.java:312)
at java.io.File.getAbsolutePath(File.java:501)
at sun.awt.shell.Win32ShellFolder2.<init>(Win32ShellFolder2.java:291)
at sun.awt.shell.Win32ShellFolderManager2.createShellFolderFromRelativePIDL(Win32ShellFolderManager2.java:66)
at sun.awt.shell.Win32ShellFolderManager2.createShellFolder(Win32ShellFolderManager2.java:56)
at sun.awt.shell.Win32ShellFolderManager2.getRecent(Win32ShellFolderManager2.java:114)
at sun.awt.shell.Win32ShellFolderManager2.get(Win32ShellFolderManager2.java:251)
at sun.awt.shell.ShellFolder.get(ShellFolder.java:227)
at sun.swing.WindowsPlacesBar.<init>(WindowsPlacesBar.java:64)
at com.sun.java.swing.plaf.windows.WindowsFileChooserUI.updateUseShellFolder(WindowsFileChooserUI.java:505)
at com.sun.java.swing.plaf.windows.WindowsFileChooserUI.installComponents(WindowsFileChooserUI.java:196)
at javax.swing.plaf.basic.BasicFileChooserUI.installUI(BasicFileChooserUI.java:136)
at com.sun.java.swing.plaf.windows.WindowsFileChooserUI.installUI(WindowsFileChooserUI.java:129)
at javax.swing.JComponent.setUI(JComponent.java:673)
at javax.swing.JFileChooser.updateUI(JFileChooser.java:1763)
at javax.swing.JFileChooser.setup(JFileChooser.java:360)
at javax.swing.JFileChooser.<init>(JFileChooser.java:333)
at javax.swing.JFileChooser.<init>(JFileChooser.java:286)
at my.pack.Main.selectRoot(Main.java:184)
查看java.io.Win32FileSystem.normalize()的源代码，似乎(当前)路径为null:
public String normalize(String path) {
int n = path.length(); // Line: 164
char slash = this.slash;
char altSlash = this.altSlash;
如果我从程序的另一点运行selectRoot()，它将运行良好...
更新
伙计们，这真是编写编程陷阱的好书!
在我的原始代码中，有一个JTextField可以保存实际路径并以这种方式进行初始化:
root = new JTextField();
root.setToolTipText("Root folder");
root.setText(System.clearProperty("user.dir"));
System.clearProperty()清除系统属性(为空)，而返回旧值(arrrghhhhhhh)。 clearProperty()可能会从自动完成中滑入。
谢谢你们。会给你一些票...
最佳答案
也许这会有所帮助
new JFileChooser(System.getProperty("user.home"));