Reputation: 5959

type casting of byte and int

I'd a code snippet:

class AutoTypeCast{
    public static void main(String...args){
        int x=10;
        byte b=20;//no compilation error
        byte c=x;//compilation error
    }
}

Why 20 is automatically type-casted to byte while x not?

Upvotes: 0

Answers (8)

Santosh

Reputation: 17923

Up-casting is automatic where as down-casting or narrowing (byte c=x;) should be explicit as it might cause loss of precision which a programmer should be aware of explicitly. To correct it you need to put an explicit cast byte c=(byte)x;

Upvotes: 0

JProgrammer

Reputation: 1135

Because compiler is not able to figure out the value of X at compile time. So it assume that X can contain value which is greater than byte range. If you make variable X as final then it will not give you compile time error.

        final int x=10;
        byte b=20;//no compilation error
        byte c=x;//no compilation error

Upvotes: 3

Foggzie

Reputation: 9821

When the compiler looks at the line

byte b=20;

it knows it's looking for a byte after b=. When it finds a constant numeric value it knows at compile time that it will definitely be in the range of byte so it will automatically cast it.

When is sees the line

byte c=x;

it's once again looking for a byte after c= but instead of finding a numeric constant, finds a variable that already has a defined type and, at compile time, can't be sure that it will be in the range of byte so you get an error.

Upvotes: 1

Alex D

Reputation: 30465

In this case x is initialized to 10, so there will be no data loss in the conversion from a 32-bit int to an 8-bit byte. But in general, when converting from int to byte, there can be data loss, so the rules of the Java language forbid assigning int values to a byte without a cast. This rule is designed to make it more difficult to write buggy code. By inserting the (byte) cast, you are effectively telling the compiler: "Yes, I have thought about the possibility of data loss, and it is not a problem here (or, that's actually what I want)."

Upvotes: 1