how to compile multiple java files when there are

问题:

I am compiling multiple files in a directory (javac *.java) but I have a problem when I try to do this:

I get compile errors saying that say javac cannot find a symbol of an object.

I have multiple packages that contain java files that are needed to run the main program. But it seems that trying to compile these one by one won't work. It runs fine in my IDE but I'm interested in learning how it's done via Command Prompt.

The main program is in the drivers folder.

I have tried compiling the files in order of dependency but that didn't work out.

回答1:

Javac documentation provides all the necessary information. However, it might be useful to use Ant or Maven for command line builds.

This page provides a good example of using first javac and then Ant for building a simple project.

---

Here is an example project and how can it be compiled with javac.

The tree structure of the project is this:

   .
    ├── build
    └── src
        ├── attacks
        ├── drivers
        │   └── Driver.java
        └── exceptions
            └── MyException.java

There are two special directories -- build for containing compiled classes and src to contain source files (could be in different subdirectories -- packages).

The following command compiles the whole project and puts the result into the build directory.

javac -sourcepath src -d build src/**/*.java

The -sourcepath src specifies directory src as the place where all the source can be found by the compiler. The -d build options tells the compiler where to place the compiled files.

Option src/**/*.java tells the compiler what files to actually compile. In this specific case it tells javac to look two levels down and pick all *.java at that level.

If there are *.java files at different levels than a list of files needs to be specified. For this, one could create such listing as an external file and pass this files as in input option for javac.

Here is how this could be done under Linux/Unix:

find -name "*.java" > source.txt

The above command creates file source.txt that contains full paths for the found *.java files. For this example it contains:

./src/drivers/Driver.java
./src/exceptions/MyException.java

In order to compile the project with the list of source files flushed into source.txt, the following command can be used:

javac -d build @source.txt

Please note that @source.txt specified at the end that tells the compiler where to look for a list of source files. Please also note that the -sourcepath option can be omitted.

Here is how the directory structure changed after running the above command.

.
├── build
│   ├── drivers
│   │   └── Driver.class
│   └── exceptions
│       └── MyException.class
└── src
    ├── attacks
    ├── drivers
    │   └── Driver.java
    └── exceptions
        └── MyException.java

As can be observed the build directory now contains the compiled class files in respective packages.

And, if you'd like to run it, assuming, for example, that Driver has method main, the following command executes the program.

java -cp .:build:**/*.class drivers.Driver

Please note that file separator : (colon) is used under Unix, for Windows change it to ; (semicolon).

回答2:

I am compiling multiple files in a directory (javac *.java)

Wrong already. That will only work correctly if the Java classes aren't in packages. The correct way to do this is as follows, where src is the name of the directory at which all your package directories are rooted:

cd src
javac package1/package2/*.java
javac package3/package4/package5/*.java

etc for whatever your package/directory layout is. Each javac command line will compile all the files in the named directory and all the .java files in other packages/directories that it depends on that aren't already compiled or that are out of date.

See the Tool documentation for javac.

回答3:

two options:

1) Use the command line to specify all files to compile

2) Create a file with all the filenames (output from find, perhaps), and run javac @argfile