How do you compile against a jar file in Java 9?

Question

Java 9 introduced the concept of modules, which do not explicitly replace jar files, but the old --classpath option seems to be gone.

The command javac --help no longer mentions the classpath.

I am trying to compile some student work against JUnit:

> javac *.java --classpath junit.jar

But I get a variety of errors, depending on what I try. For the example above:

javac: invalid flag: --classpath

My Java version is:

> java --version
java 9
Java(TM) SE Runtime Environment (build 9+181)
Java HotSpot(TM) 64-Bit Server VM (build 9+181, mixed mode)

I'm not trying to use a module, just a .jar file that I could include in IntelliJ by specifying a libs folder.

Edit: My real problem was that I was not including the correct jars. Compiling against IntelliJ's default JUnit5 configuration worked:

 javac -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2017.2.5\plugins\junit\lib\junit-jupiter-api-5.0.0.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2017.2.5\plugins\junit\lib\opentest4j-1.0.0.jar" *.java

Answer 1

You misspelled the option. According to the javac options page for Java 9:

--class-path path , -classpath path, or -cp path

Specifies where to find user class files and annotation processors. This class path overrides the user class path in the CLASSPATH environment variable.

For some reason, if you use the two hyphens option --, there is a hyphen in "classpath": --class-path. The one hyphen option - has no hyphen in "classpath": -classpath.

Any of these are valid:

javac *.java --class-path junit.jar

javac *.java -classpath junit.jar

javac *.java -cp junit.jar