[jiggy2011]

One obvious reason for this would be that colleges/universities very often teach Java as the main language and will usually encourage students to buy at least one or two books on the subject.

Another reason is that Java projects will often use some fairly heavy frameworks like hibernate, which can be great to work with if you really understand how they work. The best way to do this is to make sure you have the definitive book on your shelf as you are in for a world of pain if you just try to "wing it" like you would with PHP.

[efa]

And also Java is very popular in large corporations (at least in my experience in the Financial Services sector). These companies have large staffs and lots of money. They'll send whole teams to training classes (which includes books).

While working for these large companies I thought the whole world was Java/Spring/Hibernate. Now that I work on my own (and have started spending more time on HN) I see there is a totally different picture for the startup/consulting world.

BTW, scanning GitHub to determine language popularity seems ridiculous to me. What percent of larger corporations use GitHub (less then 5% I would guess).