The Language

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UsingHolonJ

Variables

The JVM stores data in fields. For every variable and constant a field record is created in the class file together with a field reference in the constant pool. Methods access the field via the field reference and address the field reference via its index in the constant pool.

Variables

You can create class fields (static = global for the class) and instance fields (accessible in objects).

A variable has a type. There are basic Java types and class types.

HolonJ creates a public instance field, if no attributes are given.

Syntax: (attributes) type identifier

int xxx
private Point origin
static long sum

Constants

Constants are final static fields with a fixed value.

Syntax: value final type identifier

88 final int Maximum

Arrays

The use of arrays in HolonJ is best described with some examples.

int [] [] intarray

defines a two dimensional array.

2 3 new intarray

creates an instance of intarray with lengths 2 and 3

77 is 0 1 intarray

stores a value at component 0,1

0 1 intarray

retrieves the value at component 0,1

obj intarray

delivers the object reference, e.g. for passing the array as an argument to another word.

length intarray

delivers the number of components of a one dim. array

\ Print all components of the string array args
: main ( string [] args -- )
length args times i args type loop ;

Local Variables

Syntax: type name.

: startFrame ( -- )
     frame myframe       \ defines the local variable myframe of type frame
     new myframe ( -- )   \ creates an instance of myframe
     new Calculator () myframe addComponent
     myframe packWindow ;

"()" can be used in place of "( -- )". Some constructors accept initial values. Example:

10 new myList ( int -- )

Local Arrays

Local arrays are defined and used like other arrays.

Using Fields in external packages

Fields in external packages are imported.