Think in java, notes

Where storage lives1.Registers2.The stack3.The heap4.Constant storage5.Non-RAM storage
java Primitive type:  Wrapper type1.boolean Boolean2.char 16 bits Character3.byte 8 bits Byte4.short 16 bits Short5.int 32 bits Integer6.long 64 bits Long7.float 32 bits Float8.double 64 bits Double9.void Void
High-precision numbersBigIntegerBigDecimal
---------------------------------------The key difference between Java SE5 and earlier versions of Java is that the earlier 
versions would force the overridden verion of process() to return Grain, rather than Wheat, even though Wheat is derived from Grain and thus is still a legitimate return type. Covariant return types allow the more specific Wheat return type.
Covariant 协变
legitimate   
adj.  合情合理的; 合法的