Boxing refers to a conversion of a non-nullable-value type into a reference type or the conversion of a value type to some interface that it implements (say int to IComparable<int>). Further, the conversion of an underlying value type to a nullable type is also a boxing conversion. (Caveat: Most discussions of this subject will ignore … Read more
It looks like the language in section 5.5 Casting Conversion of Java 7 JLS was updated in comparison to the same section in the Java 5/6 JLS, probably to clarify the allowed conversions. Java 7 JLS says An expression of a reference type may undergo casting conversion to a primitive type without error, by unboxing … Read more
Boxed values are data structures that are minimal wrappers around primitive types*. Boxed values are typically stored as pointers to objects on the heap. Thus, boxed values use more memory and take at minimum two memory lookups to access: once to get the pointer, and another to follow that pointer to the primitive. Obviously this … Read more
Clearly the machine code the JIT compiler can generate for the first case is much more efficient. One rule that really helps there is that an object can only be unboxed to a variable that has the same type as the boxed value. That allows the JIT compiler to generate very efficient code, no value … Read more