Conversions and Promotions - The Java Language Specification - page 95

• If T is byte , short , or int , then use new Integer( x ) .
• If T is long , then use new Long( x ) .
• If T is float , then use new Float( x ) .
• If T is double , then use new Double( x ) .
This reference value is then converted to type String by string conversion.
Now only reference values need to be considered:
• If the reference is null , it is converted to the string “ null ” (four ASCII characters n ,
u , l , l ).
• Otherwise, the conversion is performed as if by an invocation of the toString meth-
od of the referenced object with no arguments; but if the result of invoking the
toString method is null , then the string “ null ” is used instead.
The toString method is defined by the primordial class Object (§ 4.3.2 ). Many
classes override it, notably Boolean , Character , Integer , Long , Float , Double , and
String .
See § 5.4 for details of the string conversion context.
5.1.12. Forbidden Conversions
Any conversion that is not explicitly allowed is forbidden.
5.1.13. Value Set Conversion
Value set conversion is the process of mapping a floating-point value from one value set to
another without changing its type.
Within an expression that is not FP-strict (§ 15.4 ) , value set conversion provides choices to
an implementation of the Java programming language:
• If the value is an element of the float-extended-exponent value set, then the imple-
mentation may, at its option, map the value to the nearest element of the float value
set. This conversion may result in overflow (in which case the value is replaced by
an infinity of the same sign) or underflow (in which case the value may lose preci-
sion because it is replaced by a denormalized number or zero of the same sign).
• If the value is an element of the double-extended-exponent value set, then the im-
plementation may, at its option, map the value to the nearest element of the double
value set. This conversion may result in overflow (in which case the value is re-
placed by an infinity of the same sign) or underflow (in which case the value may