Why does primitive conversion involving "char" always require explicit cast?

[Thomas Markl]

Why does primitive conversion involving "char" always require explicit cast?
When I do a conversion from byte->char and vice versa it always requires cast.
If I had done this with byte->int and vice versa
then only conversion "int to byte" would have reqired explicit cast (as narrowing primitive conversion):
Conversion char to byte and vice versa

public class Question02d {
public static void main(String[] args){
char j = 'c';
byte i = j;                //line 2
                             System.out.println(i);
}
}
//Error at line 2 - Possible loss of precicion -> explicit cast neccessary!!

C:\Java\EigeneJavaProgramme>javac Question02d.java
Question02d.java:6: possible loss of precision
found : char
required: byte
byte i = j; //line 2
corrected :

public class Question02d {
public static void main(String[] args){
char j = 'c';
byte i = (byte)j;//line 1
//byte i = j; //Error at line 2 - Possible loss of precicion -> explicit cast neccessary!!
                             System.out.println(i);
}
}
[CODE]

result
C:\Java\EigeneJavaProgramme>java Question02d 
99

Conversion byte => char
[CODE]
public class Question02d {
public static void main(String[] args){
byte j = 124;
char i = (char)j;//line 1
//char i = j; ////Error at line 2 - Possible loss of precicion -> explicit cast neccessary!!
                System.out.println(i);
}
}
//Error at line 2 - Possible loss of precicion -> explicit cast neccessary!!

C:\Java\EigeneJavaProgramme>java Question02d

[Thomas Markl]

Sorry, I forgot the rest:

result
C:\Java\EigeneJavaProgramme>java Question02d
99

Conversion byte => char

public class Question02d {
public static void main(String[] args){
byte j = 124;
char i = (char)j;//line 1
//char i = j; ////Error at line 2 - Possible loss of precicion -> explicit cast neccessary!!
                System.out.println(i);
}
}
//Error at line 2 - Possible loss of precicion -> explicit cast neccessary!!

C:\Java\EigeneJavaProgramme>java Question02d

[Thomas Paul]

Since a char is unsigned, casting a byte or short can cause a loss of precision.

[Thomas Markl]

Hello Paul,
I tried out to convert long to char and vice versa. It seems that all conversions involving a number and char reqire explicit cast.
Is it so?
Ciao
Thomas

[Marilyn de Queiroz]

The general rules for primitive assignment conversion can be stated as follows:

A boolean may not be converted to any other type

a non-boolean may be converted to another non-boolean type provided the conversion is a widening conversion.

A non-boolean may not be converted to another non-boolean type if the conversion would be a narrowing conversion.

Diagram of widening conversions:

        char  \
                  int -> long -> float -> double
byte -> short /
  

[Marilyn de Queiroz]

It seems that all conversions involving a number and char reqire explicit cast.

A long is too big to fit into a char.

Conversions assigning a number variable to a char require an explicit cast. However, you can assign the int literal '45' to a char.

[Ron Newman]

A byte is not too long to fit in a char, but a byte is signed while a char is unsigned. If the value of your byte is between -128 and -1, it will be changed into some positive number.
The compiler is trying to draw your attention to this fact -- by writing an explicit cast, you can tell the compiler that you're aware of it.

[Thomas Paul]

Originally posted by Thomas Markl:
Hello Paul,
I tried out to convert long to char and vice versa. It seems that all conversions involving a number and char reqire explicit cast.
Is it so?
Ciao
Thomas

Yes it is.
Here is the chart:
byte - short - int - long - float - double
Any movement towards the right does not require a cast. Any movement towards the left requires a cast. Any movement to char (which isn't in the list) requires a cast.
[ August 31, 2002: Message edited by: Thomas Paul ]