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Java Primitive Literals

Randy Johnson

Joined: Apr 17, 2002
Posts: 22
I have verified the following statements and results:
float f1 = 1.0 --> compile error
byte b1 = 2 --> compiles and runs
byte b1 = 129 --> compile error
I understand that a literal of:
1 --> is interpreted as an int
1.0 --> is interpreted as a double
and further, that 'downcasting' requires a 'cast' opertion.
Why then, does the statement: byte b1 = 2
not generate a compile error also?
Corey McGlone
Ranch Hand

Joined: Dec 20, 2001
Posts: 3271
In the case that you use a literal to initialize a variable smaller than an int (in this case, a byte), the compiler will check to see if that literal is within the range of the variable and only cause a compiler error if the value is out of range. This is why, when yo assign the value 1 to a byte, it works and when you assign 128 to a byte, it fails (128 is outside the valid range of a byte). Java does the same thing with final variables. This code causes a compiler error:

While this code compiles and runs perfeectly:

I hope this helps,

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Valentin Crettaz
Gold Digger

Joined: Aug 26, 2001
Posts: 7610
Because as long as the literal fits within the range of the primitive type (2 is within the byte range -128,127) the compiler won't complain.
[ April 17, 2002: Message edited by: Valentin Crettaz ]

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Corey McGlone
Ranch Hand

Joined: Dec 20, 2001
Posts: 3271
As per the JLS, §5.2 Assignment Conversion:

In addition, a narrowing primitive conversion may be used if all of the following conditions are satisfied:
- The expression is a constant expression of type byte, short, char or int.
- The type of the variable is byte, short, or char.
- The value of the expression (which is known at compile time, because it is a constant expression) is representable in the type of the variable.

So, there's your answer in black and white.
Val Pecaoco
Ranch Hand

Joined: Dec 05, 2001
Posts: 156
Hi Randy,
float f1 = 1.0 --> compile error

Just for formality, from Sun's Java tutorial: "A series of digits with a decimal point is of type double. You can specify a float by putting an 'f' or 'F' after the number."
byte b1 = 129 --> compile error

Ditto with Corey and Valentin. But let's just reminisce about the basics: how do you determine the range? Since a byte has a size of 8 bits, you can determine it manually by multiplying 2 (a bit has 2 possible values, "1" or a "0", or "true" or "false") eight times (or 2 raised to the power of eight), which equals 256. Thus the range of values for the byte data type is -128 to 127 inclusive, which does not include 128. Why just 127? because you have to sneak in the special number "0" to the range (...,-1, 0, 1,...).
Ex Animo Java!
-- Val
[ April 17, 2002: Message edited by: Val Pecaoco ]

"Knowledge is power, but enthusiasm is the key." -- Lavern Barn
I agree. Here's the link:
subject: Java Primitive Literals
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