This is from https://ctan.org/pkg/javatex
The files there (on CTAN) are dated 1998-October-05.
To quote the author, Timothy Murphy:
javatex – A Java implementation of TEX
At root, this is a ‘small’ TEX (memmax=64K), but a larger version may be built.
The implementation was in essence an experiment, and performance proved so poor that the author considers it unusable in practice.
But a review there (by HeikoTheissen, dated 2017-01-27) says:
I have adapted the package in three places and find the result perfectly usable:
Fixed an error in mlist_to_hlist
Fixed an error that prevented hyphenation
Enlarged javaTEX.memoryword.maxHalfword= 1073741823 and built a `big' TEX with memmax = 10000000
Looking at the files, it appears that the author performed an automatic translation from the WEB sources into initex.java and virtex.java (and other files, all in the jtex-java directory), using the files in the jtex-src directory. Would be useful to study.