Any of those will do all that you need in Java coding. (and a lot more besides).
Of the 3, I'd probably chose the HP based on cost savings, based on what you say you're going to use it for.
HP DM1 - best available price is now $370
It's not the lightest but is the lowest price, has a 7200rpm HDD and longest running battery. HP Pavilion dm1z Review
Acer TimelineX 1830T has the more powerful ULV CPU and is the lightest of the 3 you listed. Acer Aspire TimelineX 1830T Review
Asus UL20FT didn't get an especially good review from LaptopMag so you'll want to check the article over closely. Asus UL20FT-A1 Review