java - spring difference between value and ref -

https://www.tutorialspoint.com/spring/constructor_based_dependency_injection.htm

my question in last sentence of tutorial.

 final note, in case passing reference object,   need use ref attribute of <constructor-arg> tag ,   if passing value directly should use value      attribute shown above. 

i little bit confused reference of object , value.

can primary types value, java class , beans references?

what else might used reference here?

thank much

a reference points spring bean.

a value true value being inputted. e.g. "foo" or "1"