Building jtreg is currently a two-step process:

1. download or otherwise determine all the necessary dependencies
2. run `make` to perform the build, using the dependencies found in the step 1

Step 1 is normally accomplished using the shell script `make/build.sh`.

To improve long-term maintainability, it would be good to replace it with an equivalent Java program, particularly one that can be run by the Java source launcher, available in all recent versions of JDK (since 9).