The Java® Language Specification, Java SE 7 Edition, Fourth Edition

5.2. Assignment Conversion

Assignment conversion occurs when the value of an expression is assigned (§15.26) to a variable: the type of the expression must be converted to the type of the variable.

Assignment contexts allow the use of one of the following:

• an identity conversion (§5.1.1)

• a widening primitive conversion (§5.1.2)

• a widening reference conversion (§5.1.5)

• a boxing conversion (§5.1.7) optionally followed by a widening reference conversion

• an unboxing conversion (§5.1.8) optionally followed by a widening primitive conversion.

If, after the conversions listed above have been applied, the resulting type is a raw type (§4.8), unchecked conversion (§5.1.9) may then be applied.

It is a compile-time error if the chain of conversions ...