What's the best value Java object database?

What's the best value Java object database out there that has:

• Ease of use: one line of code to store any object.
• Efficient memory usage: i.e. only loads the things that are called for, not the whole object every time (i.e. "Transparent Activation").
• Automatically change objects when manipulated (i.e. "Transparent Постоянство ").
• Собственные запросы (нет необходимости в SQL, JDOQL etc.)
• Free

where anybody has experience with the following:

• Neodatis
• db4o
• JODB
• joafip
• MyOODB

?