Reddit reviews Borobudur: Golden Tales of the Buddhas (Periplus Travel Guides)

For free overview the wiki and wikivoyage articles should be good enough to print and bring along:

• https://en.wikivoyage.org/wiki/Prambanan
  
• https://en.wikivoyage.org/wiki/Borobudur
  
  For books try these since they have kindle versions (note: I haven't read them):
  
  
• https://www.amazon.com/Java-Revealed-Borobudur-Prambanan-Indonesia-ebook/dp/B004JXVYOK
  
• https://www.amazon.com/Borobudur-Golden-Buddhas-Periplus-travel-ebook/dp/B00ADPQTWK
  
  For Indonesian travel on a wider perspective I can recommend this:
  
  
• https://www.amazon.com/Indonesia-Etc-Exploring-Improbable-Nation-ebook/dp/B00FQUDRVS
  
  Also while in Jogja have a visit to the Ullen Sentalu museum too.