Narrowing down of values while assigning

[Anonymous]

Hello All,

I have a very basic question, which is often confuses me. This is about Narrowing down of the literal values.

for eg;,

Byte b=127; // No error

Byte b=new Byte(127); //Compile error , byte expected but used int

If my assumption is correct, in the first case, value 127 is a integer literal and probably compiler would have narrowed it down to byte and autoboxed into Byte object.

But why is this not happening in the second case. Is my assumption about autoboxing and Narrowing down is wrong. Please correct me if possible.

[Anup Jadhav]

Hi Chandra,

The simple rule to remember is that Byte constructor will take a byte or a string literal of byte value.

When you say
Byte arg = new Byte(127);

you're passing the Byte constructor an int literal which it cannot autobox to a Byte wrapper.

Anup

[Zhia-zhia Xiu Bai]

but you could say
Byte b2 = new Byte(b);

[marc weber]

I think the "rules" applying to this situation have to do with conversions, as described in the Java Language Specification.

Assignment conversion occurs when the value of an expression is assigned (�15.26) to a variable...

...if the expression is a constant expression (�15.28) of type byte, short, char or int ... a narrowing primitive conversion may be used if the type of the variable is byte, short, or char, and the value of the constant expression is representable in the type of the variable.

Ref: 5.2 Assignment Conversion.

Method invocation conversion is applied to each argument value in a method or constructor invocation...

Method invocation conversions specifically do not include the implicit narrowing of integer constants which is part of assignment conversion (�5.2).

Ref: 5.3 Method Invocation Conversion.