Variables and parameters

Local variables

Local variables can be defined at the beginning of the J "block" (method body or anonymous methods). Their scope and life span are limited to their method definition. Their definition syntax takes the following form:

class_name variable_name; // or

class_name variable_name =initial_value;

A variable defined without any explicit initial value is initialized according to its type.

Type	Initial value
int	0
float	0.0
boolean	false
String	""
inStream, outStream	a stream in the closed state
other (non primitive)	empty

An explicit initial value can be a literal value, a variable already defined (local variable, attribute parameter) or an expression:

int i = 5;

int j = i;

String s = i.toString();

String n = Name;

Class c = this;

Feature[] som = PartFeature;

Predefined variables

Predefined variables are as follows:

The ... variable	represents ...
this	the current object.
StdOut, StdFile	the "standard screen" file for normal messages
StdErr	the "error standard exit" file.
NL	(New Line) String representing the passing to a new line.
Tab	(Tabulation) String representing the tabulation character.

Method parameters

Methods can have parameters. Parameters behave in the same way as local variables, and are defined as follows:

return_class class_name:method_name (in class1_name Parameter1_name,

inout class2_name parameter2_name);

In general, their form is:

Passing_mode Class_name parameter_name

Passing modes

Passing modes indicate whether the caller (the emitter of messages) should provide parameter values or whether he must wait for the resulting value.

The ... mode	defines a parameter as ...
in	input (provided by the caller).
inout	input/output (received by the caller).

Note: Techniques such as Java "wrappers" are not necessary with J.

Actual parameter types

Passing modes determine the actual parameter types that are compatible with those of formal parameters.

With the ... mode	the type of actual parameter must ...
in	be compatible (like the simple assignment) with the type of the formal parameter
inout	be identical to the formal parameter type.

Return instruction

As in Java, "return" exits the current method, with a value as parameter.

boolean Package : Generate()

{

boolean Result;//false by default

...

return Result;

"return" is also used to exit a method which returns nothing. In this case, there is no expression after "return".