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What I really want to know is: say I would create a class called "Family" in Java, and each family would have a number of "familyMembers" as member variables, would it cost any more memory to also declare for each of the "familyMembers" what "Family" they are part of? in other words, say the family Smith has 3 members, Dad, Mom and Kid, would it cost any more memory to make Family "Smith" a member variable of each familyMember: Dad, Mom and Kid?
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As has been mentioned, it will use either 32-bits or 64-bits, however if the reference is only placed in a register, it might not use any memory.
Yes, two or more references, say from parameters and/or local variables and/or instance variables and/or static variables can all reference the same object.
References have a typical size of 4 bytes on 32-bit platforms and on 64-bits platforms with heap boundary less than 32Gb (-Xmx32G), and 8 bytes for this boundary above 32Gb. This means that a 64-bit JVM usually requires 30-50% more heap space.
In a 64-bit system, object references are typically 8-byte long.
Everything costs something. If adding another class variable, it will cost in two ways. First some bytes for your declaration in the class when it is loaded and then for each reference another 4 bytes. This is because you class definition must be loaded into memory (permanent, permgen space) and because every reference is unique on your stack the 4 bytes per reference.
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unless you use the new keyword or primitive type, you only use memory needed to store the reference
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