According to my knowledge in Java, in narrowing type conversion if source in any constant which is in range of byte than the following is allowed:
byte b=10; // allowed because 10 is in range of byte and 10 is a constant
but when I type this:
byte b=10l; // this is not allowed although 10 is in range of byte and is a constant
Why so ? Can you please tell the exact rule by which these narrowing conversions take place in Java.
The technical answer is — because the spec says so. §5.2 "Assignment Contexts" of The Java Language Specification, Java SE 8 Edition, states in part:
In addition, if the expression [on the right-hand-side of an assignment statement] is a constant expression (§15.28) of type
byte,short,char, orint:
- A narrowing primitive conversion may be used if the type of the variable is
byte,short, orchar, and the value of the constant expression is representable in the type of the variable.
As for why it doesn't allow the constant expression to be of type long, I suppose it's that you never "accidentally" end up in type long. It is very convenient to be able to write byte b = 127 as a shorthand for byte b = (byte) 127 while having the compiler prevent you from erroneously writing byte b = 128 as shorthand for byte b = (byte) 128; it is not so useful to able to write byte b = 127L, specifically, because why would you need that?