JavaBasic Help

Batch Mode | Commands | Functions | Constants | Type Conversion | Operators

Welcome to JavaBasic

JavaBasic is a line command interpreter, loosely using the BASIC command set. The upper text box in the screen is the output area. The lower the input area. By default, the interpreter operates in the single line mode. Each command you enter will be executed immediately after the <ENTER> is pressed. Try to type following command:

              
              a = "Hello "
              ?  a, " World!", newline

"Hello World!" will be displayed in the output box. To run these two commands again, highlight both lines, and press <ENTER>.

You can defer the execution by press <CTRL>-<ENTER>, the cursor will move to the next line. After all commands are typed in, highlight all lines, and press <ENTER>.

Use command "Set Batch On" to switch to batch mode.

Use command "Set Batch Off" to switch back to single line mode.

! NOTE ! Click anywhere outside the JavaBasic Applet after the first command is entered if you are using NetScape Navigator 2.0, and if the system seems hang up.

JavaBasic Command

A command, or statement has following format:

      [label ] [verb ] [attributes] [;remark]

Label is an optional integer constant. It does not require to be sequential or in any order. Warning! Duplication of label is not checked.

Verb specifies the command to be executed. If no verb is specified, command let is used.

Attributes is command dependent. There are explained in detail in section Command List

Remark is an optional comment to the command. It does not affect the command in any way.

Some quick notes on the JavaBasic Command:

JavaBasic commands and variables are not case-sensitive, LET, leT, lEt are all same as let.
JavaBasic variables are type free unless you declare a variable with type restriction (see Dim). Two traditional type forcing rules are still held. Any variable ends with $ is a string type, % an integer. Please note, $, and % are considered as a part of the variable name. So, var, var$, var% are three different variables. Variable type conversion is done implicitly.

See also Dim, Type Conversion, Command List

Batch Mode

If you prefer to run a set of commands together, switch to batch mode. The other situation that you need batch mode is to use JavaBasic composite commands, such as for and if. For example:

              sum = 0
              FOR  j = 1 TO  100 
                  sum = sum + j
              NEXT

It would be much easier to work in batch mode than single line mode.

Use Set Batch On to switch to batch mode. Here is a summary of batch mode:

<ENTER> is interpreted as normal new line key.
Press <CTRL>-<ENTER> to start executing a batch program. JavaBasic will mark the end of the program with mark ";;;---". This is also the start point of next batch command. Don't remove this line unless you need combine two batch programs together.
Alternatively, you can select (highlight) the command you wish to run, and press <CTRL>- <ENTER>. Selection across the boundary of programs is allowed.
One statement per line. Multiple statements in one line are not supported, neither one statement in multiple lines.
Use command "Set Batch Off" to switch to single line mode.
Use command "Clear Command" to clear the input area.

Command List

?
;
clear
data
dim
for ... to ... step ... next
gosub
goto
if ... then ... else ... endif
input
let
load
print
rem
return
run
set

clear

Syntax:

clear [screen | name | data | command | all | variable-name-list]

clear screen (default) clears output area.
clear data clears the data declared by data statement
clear name clears all variables from the memory.
clear command clears the input area.
clear all clears screen, command and data.
clear variable-name-list clears the definition of all variables specified in the name list. Names are separated by comma(,). If a variable name is not defined, clear will ignore it.

See also Command List

data

Syntax:

data value-list

Define the data for input command. Data will be arranged in the order the data statements appear in the command set, regardless the program control.
Use clear data to remove all data loaded.

See also Command List, Input

dim

Syntax:

dim varname [[ '['[size [, base] ] ']' ]...] [as type] [, varname [as type] ...]

Declare one or more variables. type must a pre-defined variable type. Current available types are integer, double, boolean and string.
Only one dimension array is directly supported. However, you can recursively define array of array to make it multiple dimensions. For example

              dim a[2][3]

defines a two dimension array. If the size is omitted, the array will be treat as a free size array, i.e., its size will expanded automatically as necessary. For a given size array, out of range error occurs when index in not inside the range. Array base is always 1.

See also Command List

for ... to ... step ... next

Syntax:

for control-variable = initial-expression to upper-bound-expression [step step-expression] do

command-list

next [control-variable]

Control-variable is always considered as type integer;
Initial-expression, upper-bound-expression, step-expression are all considered as integer type. upper-bound-expression and step-expression will be evaluated every time after the loop is performed.
If initial-expression > upper-bound expression, and step-expression is >0, no command will be executed.
Default step is 1
The next statement always matches the closest open for statement. The control-variable is the next statement will be checked against the for statement if presented.
For-next must either all in, or all out of if -endif block.
Jump into a for loop is not allowed.

See also Command List

gosub

Syntax:

gosub label

label is an integer constant. Program control will transfer to the statement specified by the label, and running until the end of program is reached, or a return statement reached. Then, the program will return back to the next statement following the gosub statement.
Note : if ... gosub is not currently supported.

See also Command List, Goto, if...endif, for...next

goto

Syntax:

goto label

label is an integer constant. Program control will unconditionally transfer to the statement specified by the label.

Jumping into a if-endif block, or for-next loop is not allowed.

Note : if ... goto is not currently supported.

See also Command List, Gosub

if ... then ... else ... endif

Syntax

if Boolean-expression then

command-list-1

[ else

command-list-2]

endif

or

if Boolean-expression-1 then

command-list-1

else if Boolean-expression-2 then

command-list-2

[ else

command-list-3]

endif

See also Command List

input

Syntax:

input variable-name-list

variable-name-list is a comma separated list of variables. This statement will read data from the data statement. If it reaches the end of the data statement, it will start back from the beginning.

See also Command List, Data

let

Syntax:

[ let] left-value = expression

Assign the value of the expression to a variable specified by left value. In JavaBasic, the behavior of the assignment operator is defined by the left value.
Left value can be:

a non-array variable name, for example a = 1, a$ = "hello world"
a function, for example, button("OK", "color") = red
a component of an array, customer[editing] = "Hello World, Inc."

See also Command List

load

Sorry, not implemented yet!

See also Command List

print / ?

print expression-list

or

? expression-list

Print the value of all expressions onto the screen.

See also Command List

rem / ;

Syntax:

rem [any thing]

or

; [any thing]

Make a remark or comment. Only ; is allowed as the end of line comment. Anything after the ";" in a line will be discarded by command interpreter.
Example:

              rem this line doing nothing
              ; this line doing nothing either
              j = j + 1 ; increase the counter

See also Command List

return

Syntax:

return

Return from a subroutine. If there is no gosub call before reaching a return statement, the program ends.

See also Command List, Gosub

run

Syntax:

run url-string

Run a JavaBasic script file specified by the url-string. A relative url-string is accepted, which is related to the HTML document locations. The script will be loaded and executed if no error is found.

See also Command List

set

Syntax:

set batch on / off

Set the system variables.
Set batch on/off turns on/off the batch processing mode. In the batch process mode, command will be executed together when user pressed <CTRL>-<ENTER>. In the single line mode, command will be executed line by line immediately after it is typed in.

See also Command List

Function List

abs(double)	Returns the absolute double value of a.
acos(double)	Returns the arc cosine of a, in the range of 0.0 through Pi.
asin(double)	Returns the arc sine of a, in the range of -Pi/2 through Pi/2.
atan(double)	Returns the arc tangent of a, in the range of -Pi/2 through Pi/2.
cos(double)	Returns the trigonometric cosine of an angle.
exp(double)	Returns the exponential number e(2.718...) raised to the power of a.
log(double)	Returns the natural logarithm (base e) of a.
random(double)	Generates a random number between 0.0 and the given range.
sin(double)	Returns the trigonometric sine of an angle.
sqrt(double)	Returns the square root of a.
tan(double)	Returns the trigonometric tangent of an angle.

Constants

Note, all constants can be overridden by assigning a new value to it, or declare a variable with the same name.

newline New line ("\n")

tab Tab ("\t")

pi Mathematical constant

e Mathematical constant

true Boolean constant

false Boolean constant

Type Conversion

Types are automatically converted where necessary and possible. In the calculation, generally speaking, right operand is converted to the type of left operand. For example

              ? 1 + "23 "  ;will produce 24
              ? "23" + 1  ;will produce "231"
              ? 1-"23"  ;will produce -22
              ? "23"-1  ;will produce an error message.

Other rules in conversion:

Boolean type only can be converted to string type, with value "false" and "true"

String type can be converted to a Boolean value true of it is "true", otherwise always false.

Operators

Arithmetic Operator

+  (addition)            - (subtraction)
*  (multiplication)      / (division)
^  (power)

Logic Operator (List in order of preference)

> (greater than)         >= (not less than)     < (less than)
>= (not greater than)    = (equal)              != (not equal)
& (And)                  | (Or)