Java程序无法从命令提示符执行

Question

I recently installed a java software in my PC and started writing some simple programs. I didn't face any problem while compiling the programs, but while executing it, it shows this error message -

"Windows can't open this file.

File: HelloWorld.java

To open this file, windows need to know what program you want to open it. Windows can go online to lookup it automatically, or you can manually select from a list of programs that are installed on your computer.

I know all the path settings are correct. In fact, there was no problem at all while compiling the program. What can be the problem of this? I even reinstalled JRE and that didn't help. Can someone help me?

Note: I'm using Windows 7 64 bit architecture OS and I'm using command prompt for compilation and execution of the file.

Answer 1

I'll assume that you've double-clicked the .java file, eg in the file explorer. A java source file isn't a (click-launchable) executable, and - without some acrobatics - neither is a compiled .class file: you shouldn't expect to double-click either and start your program.

In order to get this sort of behavior, you'll need to build a launchable program, and there are a few ways to do this. One is by making a batch file that runs the java VM with your code, another is creating an executable jar file.

To just run your code outside your IDE, you can invoke the java VM on the command line:

c:\> java HelloWorld

As to your specific error message, you haven't associated any program with .java files. Typically, as programmers, we want this Windows file association to be our editor of choice or our IDE. You can create this association by Right-clicking on the file, choosing Properties from the menu and then clicking the Change button beside Opens with: to pick an application.

But this is a side-issue: you still won't use this to make .java file executable. Search around this site for questions and answers about building executable jar files. If you're using a specific IDE like Eclipse or NetBeans, use that to refine your search.

Answer 2

When you want to execute the program, you specifiy the class name rather than the file name:

java HelloWorld

Don't use java HelloWorld.java , for instance.