IMO, HP anything is a non-starter. Carly Fiorina may be gone from the company, but her legacy of driving the computer business into the ground quality wise still remains. It was after her reign that someone in HP had the brilliant idea of stuffing desktop CPUs into laptops, then the things were literally melting the cases from the heat they generated. They're far from alone on idiotic stunts like that, but HP's computer business is one of a bottom feeder. Ever since HP and Compaq merged, ending their epic struggle to be the world's worst computer manufacturer, Acer stepped in to challenge them for the toilet bowl crown and that race to the bottom has been going on for the past 11 years or so.
You can always write Java code on a Mac, you just won't be able to test it outside of the conditions I outlined unless something changes.
I've worked as a hardware tech for the past couple of years, and I'll just share my personal opinions with you on the various brands.
Acer/Gateway/eMachines: Pure garbage. Wouldn't touch them with a stolen 10ft pole. If you buy an Acer system, expect to do any and all support yourself, including hardware. Your warranty will be of more use as toilet paper than it will in getting your system fixed.
HP/Compaq: Also pure garbage, wouldn't touch with a stolen 10ft pole. Systems made pre-2000ish might not be too bad, but obviously aren't going to be the best for use today. HP is big on using odd proprietary bits of hardware like a HDD docking bay that only accepts drives with a special connector that naturally only HP licenses. You will probably get your system fixed under warranty... Eventually. If their computer business is anything like their printer business, expect to wait 1-2 weeks, maybe more, for the warranty part to even arrive.
Lenovo: They still have a little ways to go before reaching the levels of HP and Acer, but not for a lack of trying. They've done an admirable job of taking IBM's computer business, which was probably the #2 in quality at the time of sale, and driving it into the ground. Word has it, even IBM has finally dumped Lenovo in favor of Toshiba to outfit everyone with laptops in the company. One particular example I like to give for Lenovo, is I was working on a ThinkPad one time, and they literally taped (with scotch tape) one of the wireless card antenna cables to the CPU heatsink. That one was a real head scratcher for me, and I still haven't figured out *** they were thinking. Assuming the cable doesn't one day melt, the shielding of the insulation is likely not going to be sufficient to block out all the noise generated by the CPU.
Toshiba: If you avoid their low and high end units, they're not bad. They're not great, but they're not bad. Getting warranty repairs is another story. I've literally waited about a month to get warranty parts from Toshiba... On NUMEROUS occasions. The good news is that their build quality is usually good enough that repairs should be infrequent.
Sony and Fujitsu I have no experience with, so can't really comment.
Dell: Like Toshiba, except they have much better warranty support. Dell doesn't tend to screw around with warranty repairs. They do a good job of stocking repair parts, and parts usually arrive within 2-3 business days. You take a system in for repair, it'll probably be back in your hands within a week.
Apple: By far and away the best I've seen. Design and build quality coming together in a very nice symbiotic way. While other companies all use plastic, most Apple models use metal cases. Even the MacBook, which has a plastic case, feels like a higher quality of plastic compared to other computers. I do have some gripes about the screws used internally on some models, which tend to strip out very easily, but odds are that won't be your problem. Apple does not screw around with warranty repairs either, and Apple has financial incentives in place for repair shops to turn things around quickly, but also making sure they get the job done right the first time. Repair parts usually ship out within 24 hours, they arrive within 2-3 business days (most of the time it's because FedEx screwed up if things take longer) and like Dell, you'll likely be in and out within a week.
Again, these are just my opinions, take them for whatever they're worth to you.