Build them for what? Does Travis create an executable JAR as a package?
I use Jenkins; not familiar with Travis. For any CI tool, you will need to execute a script.
Can you just create them?
Oh sure. If you want to ask Travis to run javac for you, be sure to do it using any hooks that he will give you.
Otherwise, how would I convert the project to ANT or Maven?
If you are confused, start with Ant. You would build.xml using the <javac> task. You do not have to change anything with your current project.
I would recommend Maven, except that you are confused. Maven helps you manage your dependencies and the life cycle. You will need to modify your project to match the standard Maven directory structure and create pom.xml .