The Java Language Specification, Third Edition

CONVERSIONS AND PROMOTIONS Narrowing Reference Conversions 5.1.6
• byte to char
First, the byte is converted to an int via widening primitive conversion, and then
the resulting int is converted to a char by narrowing primitive conversion.
5.1.5 Widening Reference Conversions
A widening reference conversion exists from any type S to any type T, provided S
is a subtype (§4.10) of T.
Widening reference conversions never require a special action at run time and
therefore never throw an exception at run time. They consist simply in regarding a
reference as having some other type in a manner that can be proved correct at
compile time.
See §8 for the detailed specifications for classes, §9 for interfaces, and §10 for
arrays.
5.1.6 Narrowing Reference Conversions
The following conversions are called the narrowing reference conversions :
• From any reference type S to any reference type T, provided that S is a
proper supertype (§4.10) of T. (An important special case is that there is a narrowing
conversion from the class type Object to any other reference type.)
• From any class type C to any non-parameterized interface type K, provided
that C is not final and does not implement K.
• From any interface type J to any non-parameterized class type C that is not
final.
• From the interface types Cloneable and java.io.Serializable to any
array type T[].
• From any interface type J to any non-parameterized interface type K, provided
that J is not a subinterface of K.
• From any array type SC[] to any array type TC[], provided that SC and TC
are reference types and there is a narrowing conversion from SC to TC.
DRAFT
Such conversions require a test at run time to find out whether the actual reference
value is a legitimate value of the new type. If not, then a ClassCastException is
thrown.
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