listFiles 方法 遍历文件夹时报空指针异常的原因

错误信息  

Exception in thread "main" java.lang.NullPointerException

public static void test02(File file){
        System.out.println("当前file = " + file);
        File[] files = file.listFiles();
        for (File file1 : files) {
            if (file1.isDirectory()){
                test02(file1);
            }else {
                if (file1.getName().endsWith(".java")){
                    System.out.println("file1 = " + file1.getName());
                }
            }
        }
    }
}

输出

......
当前file = D:System Volume Information
Exception in thread "main" java.lang.NullPointerException
	at dayTest.test08.JavaCode08.test02(JavaCode08.java:34)
	at dayTest.test08.JavaCode08.test02(JavaCode08.java:36)
	at dayTest.test08.JavaCode08.main(JavaCode08.java:16)

可见,当遍历到系统文件且没有权限时,遍历的file对象是null,此时会抛出空指针异常