尝试在命令行上运行时，Java“无法找到或加载主类”

Question

I have a java project with the directory structure as follows:

java 
   | build
   | src
     | gui
         |  Launcher.java

I am compiling the program to a .class file using the command:

find -name "*.java" > src.txt
javac -d build @src.txt
rm $src.txt

After compilation the project directory looks like this

java 
   | build
     | gui
        |   Launcher.class 
   | src
     | gui
         |  Launcher.java

When I try to run the program (main is in Launcher.java) with:

java -cp .:build:**/*.class gui.Launcher

I get an error saying:

Error: Could not find or load main class gui.Launcher

Anyone see whats wrong?

note: I am using cygwin on windows for this

Answer 1

Because your classpath syntax is off.

java -cp .:build:**/*.class gui.Launcher

should be (on Unix)

java -cp .:build/ gui.Launcher

or (on Windows)

java -cp .;build/ gui.Launcher

Answer 2

The other answer is correct for Linux/Unix and for Windows (without Cygwin). However, when working with Java from Cygwin there's a mismatch in that Cygwin is trying to act like Linux/Unix, but Java is a Windows binary and so it doesn't understand the Linux/Unix path syntax.

Here's what you need to do when running java (or javac ) with a class path from Cygwin. First use a semicolon as the path separator, and second put the whole path in quotes:

java -cp 'some/directory;path/to/file.jar;etc' main.class.Name <arguments>

Note that you can also try using the cygpath utility to convert a Linux/Unix style path to a Windows format that Java can understand.