Boxing and Widening

Question

What is the difference between these two. I know Boxing is converting primitive values to reference. What is widening. Also what should be the sequence first boxing should be done or widening should be done?

Answer 1

1. Widening wins over boxing and var-args
2. Boxing wins over var-args
3. Widening of reference variable depends on inheritance(so, Integer cannot be widened to Long. But, Integer widened to Number).
4. Widen and boxing is not possible
5. Boxing and widening is possible
6. var-args can be combined with either boxing or widening

Answer 2

Widening is transforming a variable in another with a wider type.
Widening can be done with primitive or reference types.

For example :

String -> Object
int -> long

As the JLS states :

a boxing conversion (§5.1.7) [is] optionally followed by a widening reference conversion

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Resources :

• JLS - Widening Primitive Conversion
• JLS - Widening Reference Conversions