initializing primitive variables with numeric literals

[Richard Legué]

If I initialize a byte or short variable with a numeric literal - for instance 'byte x = 100', the compiler doesn't complain although a numeric literal is seen by de compiler as an int-type. I don't need a cast to make this initialization work. But when I'm passing a numeric literal as a parameter to a method that takes a byte, the compiler complains about 'incompatible types'. for instance - 'public void takeArgs(byte x){ }' called by 'takeArgs(100);' makes the compiler complain. Changing the method call in 'takeArgs (byte 100) makes the code compile. I'm confused; both examples have to do with initialization (right?) but are treated differenly. Can somebody tell me why this is? Thanks

[Pete Letkeman]

/*
this works because you are setting the value to a number which is in the byte range and you are casting the value to a byte type
if you tried byte x = 300; you would get an error
*/
byte x = 100; 

public void takeArgs(byte x){ }


/*
// unless otherwise stated all whole numbers are treated as type integer, so this doesn't work 
takeArgs(100); //you are not casting the value to type byte here, so the compiler treats it as an integer
*/

/* 
you are casting the value to type byte
*/
takeArgs ((byte) 100) 

What is the value  that is passed to the method when you do this? You may be surprised.

takeArgs((byte) 300);

[Henry Wong]

Conversions for assignments are defined by section 5.2 of the Java Language Specification ... https://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.2

Conversions for Method calls (passed values) are defined by section 5.3 of the JLS ... https://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.3

Noticed that there is a part regarding "compile time constants" in section 5.2, but this part does not exist in section 5.3?

Anyway, it does make sense right? If you are the compiler, and you are generating code for the method, how the heck are you going to detect that it is a compile time constant? The calling code may be in a completely different class, may be in many classes, and may even be in classes that haven't been written yet.

Henry

[Richard Legué]

Thanks for you help. Learning all the time!

[Junilu Lacar]

Pete Letkeman wrote:

/*
this works because you are setting the value to a number which is in the byte range and you are casting the value to a byte type
if you tried byte x = 300; you would get an error
*/
byte x = 100;

There is no casting happening on line 5: You're simply declaring a byte type variable and initializing it with a literal value. The conversion for assignments that Henry referred to above is what determines whether the line will compile or not. The compile-time error that occurs if you tried to initialize it with the literal 300 is because the compiler recognizes that 300 can't be represented as a byte, not because it can't cast it to a byte.

If you cast the value, it will compile but it won't necessarily give you the same value:

byte x;

x = (byte) 300;         // compiles but chops off significant bits
System.out.println(x);  // 44 - what's left after casting

x = (byte) 100;         // only zeros chopped off
System.out.println(x);  // 100