Java - why does char get implicitly cast to byte (and short) primitive, when it shouldn't?

Question

Certain functionality of the compiler puzzles me (Oracle JDK 1.7 using Eclipse).

So I\'ve got this book that says char primitive needs to be explicitly cast to short

Answer 1

This is called compile-time narrowing of constants. It is described in section 5.2 of the Java Language Specification:

The compile-time narrowing of constants means that code such as:

byte theAnswer = 42;

is allowed. Without the narrowing, the fact that the integer literal 42 has type int would mean that a cast to byte would be required.

Same goes for character literals: if its value fits in a byte, no conversion is required; if the value does not fit, you must put in a cast, or you would get a compile error.

For example, this would not compile:

byte bc = '\uff12'; // Does not compile without a cast

but this compiles fine:

byte bc = (byte)'\uff12';