脑血管畸形头痛怎么办:jdk问题，求助

我安装了jdk，变量什么的都设好了，
在dos下输入 javac 显示
Usage: javac <options> <source files>
where possible options include:
-g Generate all debugging info
-g:none Generate no debugging info
-g:{lines,vars,source} Generate only some debugging info
-nowarn Generate no warnings
-verbose Output messages about what the compiler is doing
-deprecation Output source locations where deprecated APIs are us
ed
-classpath <path> Specify where to find user class files
-sourcepath <path> Specify where to find input source files
-bootclasspath <path> Override location of bootstrap class files
-extdirs <dirs> Override location of installed extensions
-d <directory> Specify where to place generated class files
-encoding <encoding> Specify character encoding used by source files
-source <release> Provide source compatibility with specified release
-target <release> Generate class files for specific VM version
-help Print a synopsis of standard options

但我输入javac HelloWorld.java 时显示：

error: cannot read: HelloWorld.java
1 error

大小写也没什么问题，我把安装程序放在c盘，编的记事本文挡放在e盘的，有什么问题啊？