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Welcome to the JJ commands page. This page introduces you the commands used in JJ.
Each JJ command starts with a JJ command word. JJ command words all start with a capital letter. So, if you are starting an command, remember that the first word always starts with a capital letter.
COMMANDS, COMMENTS, BLANK LINES
JJ allows commands to be combined with comments and blank lines. (Comments and blank lines are allowed for better description and readability of your JJ code.)Every line is either a command, a comment or a blank line.
Comments
Comments start with '--' and are followed with commentary for anybody that may be reading your JJ commands. For example:-- This is a comment. Notice that it starts with '--'Comments are also allowed at the end of a command. For example:
Box rate ofType int --hourly rate
Blank lines
Blank lines are used as a visual aid for your reader. For example, take a look at a list of Box commands written with and without a blank line:
Box studentName ofClass Str
Box studentID ofType int
Box studentAddress ofClass Str
Box teacherName ofClass Str
Box teacherOffice ofClass Str
Box teacherOfficeHours ofClass Str
-- now, with a blank line as a separator
Box studentName ofClass Str
Box studentID ofType int
Box studentAddress ofClass Str
Box teacherName ofClass Str
Box teacherOffice ofClass Str
Box teacherOfficeHours ofClass Str
-- A blank line helped in the above example, but consider
-- a different style and decide for yourself if a blank
-- line would help readability.
Box studentName ofClass Str
Box studentID ofType int
Box studentAddress ofClass Str
Box teacherName ofClass Str
Box teacherOffice ofClass Str
Box teacherOfficeHours ofClass Str
Commands
Command introduction
When you first begin using JJ you are likely writing small programs, consisting of about a dozen commands. When you are writing small programs, your first command can be: Box, Boxes, Output, Outputln, If or Repeat. Once you start writing larger programs, your first command will always be the Import command, and your program will always have a Class and an EndClass command.Commands by Categories
DECLARE YOUR BOXES BEFORE ANY ACTION COMMANDS
- Box
- Boxes
ACTION COMMANDS
ACTION: ASSIGNMENT
- Set
- Inc
- Dec
ACTION: INPUT/OUTPUT
- Input
- Output
- Outputln
ACTION: CHOICE
- If
- ElseIf
- Else
- EndIf
ACTION: LOOPING
- Repeat
- ExitOn
- EndRepeat
Commands by Alphabetized List
Here is an alphabetized list of commands you can use when you are first beginning and do not have any Import, Class or EndClass commands in your program: (Click on a word to jump down to a description of the rules for that command.)Command Rules
Here is an overview of the rules for commands you can use when you are first beginning and do not have any Import, Class or EndClass commands in your program:- Box
In a Box command, you must always supply the NAME for the box and the type(int, real, bool) or class(Str, ...) for the Box.
--EXAMPLES: Box NAME1 ofType int Box NAME2 ofType real Box NAME3 ofType bool Box NAME4 ofClass Str --for now, 'Str' is the only class you know about Box 34 ofType int --bad name --CheckIt error Box X34 ofType BadType --bad type --CheckIt error Box X35 ofType Str --bad type --CheckIt error Box X36 ofClass int --bad class --CheckIt error- Boxes
The Boxes command is much like the Box command. In a Boxes command, you must always supply the NAMEs for the boxes and the type(int, real, bool) or class(Str, ...) for the Boxes. A Boxes command has the exact same effect as a list of Box commands. Only use a Boxes command if your list of boxes do not require commentary to describe what the individual boxes are being used for.
You must have at least two NAMEs in a Boxes command.
--EXAMPLES: Boxes num1, num2, num3 ofType int --three boxes for input numbers Boxes firstName, lastName ofClass Str Boxes middleName ofClass Str --only one box name --CheckIt error- Dec
In a Dec command, you must always supply the NAME for the box that you want to decrement and the amount you want to decrement the box by. Both the NAME and the amount must be of type int.
There are four commands that can change the value in a box (Dec is one of these four):
- Dec
- Inc
- Input
- Set
--EXAMPLES: Dec num1 by 1 -- decrement box 'num1' by 1 Dec num2 by 33 -- decrement box 'num2' by 33 Dec num3 by num1+num2 -- decrement num3 by num1+num2 Dec num1 by 1.5 --bad 'by' value --CheckIt error Dec num1 by "1" --bad 'by' value --CheckIt error Dec 10 by 5 --bad NAME --CheckIt error- Else
An Else command is one of the CHOICE commands (If, ElseIf, Else and EndIf). An Else command must be between an If command and an EndIf command. That is, if you have an Else command at all for an If/EndIf:
- There can only be one Else command (if you decide to have one)
- The Else command must come after any ElseIf commands for this If/EndIf.
- Every command in this CHOICE must start in the same column
--EXAMPLES: -- BELOW ELSE IS IN THE CORRECT POSITION If (num1 == num2) then --do something here ElseIf (num1 < num2) then --do something different here Else --do something even different here EndIf -- BELOW ELSE IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) If (num1 == num2) then --do something here Else --do something even different here ElseIf (num1 < num2) then --CheckIt error --do something different here EndIf -- BELOW ELSE IS *NOT* IN THE CORRECT COLUMN (ERROR) If (num1 == num2) then --do something here ElseIf (num1 < num2) then --do something different here Else --CheckIt error --do something even different here EndIf- ElseIf
An ElseIf command is one of the CHOICE commands (If, ElseIf, Else and EndIf). An ElseIf command must be between an If command and an EndIf command. If you have any ElseIf command for an If/EndIf:
- There can as many ElseIf command as you like
- The ElseIf commands must all come before an Else commands (if you have an Else command) for this If/EndIf.
- The EXPRESSION in the ElseIf command must be of type bool (it must evaluate to the value of true or false. In other words, it must answer a yes/no question)
- Every command in this CHOICE must start in the same column
--EXAMPLES: -- BELOW ELSEIFS ARE IN THE CORRECT POSITION If (quizAverage < 60) then Outputln "Your average is below 60" ElseIf (quizAverage < 70) then Outputln "Your average is below 70" ElseIf (quizAverage < 85) then Outputln "Your average is below 85" Else Outputln "Your average is 85 or higher!" EndIf -- FINAL ELSEIF IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) If (quizAverage < 60) then Outputln "Your average is below 60" ElseIf (quizAverage < 70) then Outputln "Your average is below 70" ElseIf (quizAverage < 85) then Outputln "Your average is below 85" Else Outputln "Your average is 85 or higher!" ElseIf (quizAverage > 95) then --CheckIt error Outputln "Your average is 95 or higher" EndIf -- FINAL ELSEIF IS *NOT* IN THE CORRECT COLUMN (ERROR) If (quizAverage < 60) then Outputln "Your average is below 60" ElseIf (quizAverage < 70) then Outputln "Your average is below 70" ElseIf (quizAverage < 85) then --CheckIt error Outputln "Your average is below 85" Else Outputln "Your average is 85 or higher!" EndIf -- BELOW ELSEIF IS *NOT* OF TYPE BOOL (ERROR) If (quizAverage < 60) then Outputln "Your average is below 60" ElseIf (quizAverage < 70) then Outputln "Your average is below 70" ElseIf (quizAverage < 85) then Outputln "Your average is below 85" ElseIf (100) then -- 100 is an int, not bool --CheckIt error Outputln "Your average is 100" Else Outputln "Your average is 85 or higher!" EndIf- EndIf
An EndIf command is one of the CHOICE commands (If, ElseIf, Else and EndIf). An EndIf command must match with an earlier If command. Thus, the total number of EndIf commands must equal the total number of If commands.
- There must be one EndIf command for each If command
- The EndIf command must come after its matching If command
- Every command in this CHOICE must start in the same column
--EXAMPLES: -- BELOW ENDIF IS IN THE CORRECT POSITION If ((num1 == num2) and (num2 == num3)) then Outputln "All three numbers are equal" EndIf -- BELOW ENDIF IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) EndIf --CheckIt error If ((num1 == num2) and (num2 == num3)) then Outputln "All three numbers are equal" -- BELOW ENDIF IS MISSING A MATCHING IF COMMAND (ERROR) If ((num1 == num2) and (num2 == num3)) then Outputln "All three numbers are equal" EndIf EndIf --CheckIt error -- BELOW ENDIF IS *NOT* IN THE CORRECT COLUMN (ERROR) If ((num1 == num2) and (num2 == num3)) then Outputln "All three numbers are equal" EndIf --CheckIt error- EndRepeat
An EndRepeat command is one of the LOOPING commands (Repeat, ExitOn and EndRepeat). An EndRepeat command must match with an earlier Repeat command. Thus, the total number of EndRepeat commands must equal the total number of Repeat commands.
- There must be one EndRepeat command for each Repeat command
- The EndRepeat command must come after its matching Repeat command
- Every matching Repeat/EndRepeat command must start in the same column
--EXAMPLES: -- BELOW ENDREPEAT IS IN THE CORRECT POSITION Repeat Inc total by 1 ExitOn (total > 100) EndRepeat -- BELOW ENDREPEAT IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) EndRepeat --CheckIt error Repeat Inc total by 1 ExitOn (total > 100) -- BELOW ENDREPEAT IS MISSING A MATCHING REPEAT COMMAND (ERROR) Repeat Inc total by 1 ExitOn (total > 100) EndRepeat EndRepeat --CheckIt error -- BELOW ENDREPEAT IS *NOT* IN THE CORRECT COLUMN (ERROR) Repeat ExitOn (total > 100) EndRepeat- ExitOn
An ExitOn command is one of the LOOPING commands (Repeat, ExitOn and EndRepeat). An ExitOn command must be between a Repeat and an EndRepeat insruction. An ExitOn command must match with an earlier Repeat command and a later EndRepeat command. Thus, the total number of ExitOn commands must equal the total number of EndRepeat commands as well as the total number of Repeat commands.
- There must be one ExitOn command for each Repeat/EndRepeat
- The ExitOn command must come between its matching Repeat/EndRepeat
- The EXPRESSION in the ExitOn command must be of type bool (it must evaluate to the value of true or false. In other words, it must answer a yes/no question)
--EXAMPLES: -- BELOW EXITON IS IN THE CORRECT POSITION Repeat Outputln "Enter a number, or zero to exit" Input num ExitOn (num == 0) Inc total by num EndRepeat -- BELOW EXITON IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) Repeat Outputln "Enter a number, or zero to exit" Input num Inc total by num EndRepeat ExitOn (num == 0) --CheckIt error -- BELOW EXITON IS *NOT* OF TYPE BOOL (ERROR) Repeat Outputln "Enter a number, or zero to exit" Input num ExitOn (0) -- 0 is an int, not bool --CheckIt error Inc total by num EndRepeat- If
An If command is one of the CHOICE commands (If, ElseIf, Else and EndIf). An If command must match with a later EndIf command. Thus, the total number of If commands must equal the total number of EndIf commands.
- There must be one If command for each EndIf command
- The If command must come before its matching EndIf command
- The EXPRESSION in the If command must be of type bool (it must evaluate to the value of true or false. In other words, it must answer a yes/no question)
- Every command in this CHOICE must start in the same column
--EXAMPLES: -- BELOW IF IS IN THE CORRECT POSITION If ((num1 == num2) and (num2 == num3)) then Outputln "All three numbers are equal" EndIf -- BELOW IF IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) If ((num1 == num2) and (num2 == num3)) then Outputln "All three numbers are equal" --no matching EndIf, so either the end of JJ code or end method EndRoutine --CheckIt error -- BELOW IF IS *NOT* OF TYPE BOOL (ERROR) If ("Hello") then -- "Hello" is a Str, not bool --CheckIt error EndIf- Inc
In an Inc command, you must always supply the NAME for the box that you want to increment and the amount you want to increment the box by. Both the NAME and the amount must be of type int.
There are four commands that can change the value in a box: (Inc is one of these four):
- Inc
- Dec
- Input
- Set
--EXAMPLES: Inc num1 by 1 -- increment box 'num1' by 1 Inc num2 by 33 -- increment box 'num2' by 33 Inc num3 by num1+num2 Inc num1 by 1.5 --bad 'by' value --CheckIt error Inc num1 by "1" --bad 'by' value --CheckIt error Inc 10 by 5 --bad NAME --CheckIt error- Input
In an Input command, you must always supply one NAME for the box that you want to set to be value of the input read in from the keyboard.
There are two commands that can put an initial value into an empty box (Input is one of these two):
- Input
- Set
- Input
- Set
- Inc
- Dec
--EXAMPLES: Input num -- computer waits for you to enter a value Input 14 -- bad NAME --CheckIt error Input "hello" -- bad NAME --CheckIt error Input num1, num2 -- more than one NAME --CheckIt error- Output
In an Output command, you must always supply one EXPRESSION for the value that you want sent to the screen. The Output command does not conclude with a new line. The Outputln commands, on the other hand, does start a new line of output.
--EXAMPLES: Output "Hello" Output " from JJ" -- outputs 'Hello from JJ' to the screen Output num1, num2 -- more than one value --CheckIt error Output -- value is missing --CheckIt error- Outputln
In an Outputln command, you must always supply one EXPRESSION for the value that you want sent to the screen. The Outputln command concludes with a new line. The Output commands, on the other hand, does not start a new line of output.
--EXAMPLES: Outputln "" Outputln "Hello" Outputln "" Outputln " from JJ" Outputln "" -- outputs the following to the screen (without the '--'s): -- -- Hello -- -- from JJ -- Outputln total, num -- more than one value --CheckIt error Outputln -- value is missing --CheckIt error- Repeat
A Repeat command is one of the LOOPING commands (Repeat, ExitOn and EndRepeat). A Repeat command must match with an later EndRepeat command. Thus, the total number of Repeat commands must equal the total number of EndRepeat commands.
- There must be one Repeat command for each EndRepeat command
- The Repeat command must come before its matching EndRepeat command
- Every matching Repeat/EndRepeat command must start in the same column
--EXAMPLES: -- BELOW REPEAT IS IN THE CORRECT POSITION Repeat Input num ExitOn (num == 0) Inc total by num EndRepeat -- BELOW REPEAT IS *NOT* IN THE CORRECT COMMAND POSITION (ERROR) Repeat Input num ExitOn (num == 0) Inc total by num --no matching EndRepeat, so either the end of JJ code or end method EndRoutine --CheckIt error- Set
In a Set command, you must always supply both the NAME for the box that you want to set and the value you want to set the box equal to. Both the NAME and the amount must be of the same type (int, real, or bool) or be of the string class (Str).
- The type or class of the NAME must match the type or class of the value.
- The NAME is often called LHS, which stands for Left Hand Side of the '='
- The value is often called RHS, which stands for Right Hand Side of the '='
There are two commands that can put an initial value into an empty box (Set is one of these two):
- Set
- Input
- Set
- Input
- Inc
- Dec
--EXAMPLES: Set total = 0 -- total box now has a zero in it Set total = num1 + num2 -- total box now has value of num1 + num2 Set total = total + 1 -- total box now has value of total + 1 --Note that the previous command has the same effect as -- the command: Inc total by 1 -- BELOW, THE RHS(REAL) DOES *NOT* MATCH LHS(INT) (ERROR) Box b ofType int Set b = 1.5 --CheckIt errorCommand Order
Commands usually must be in a specific order. For example, if you have a Box command, it must come before any action commands. Sometimes, related commands are not order specific. For example, Box and Boxes commands can usually be in any order.The below categories discuss the specific command order for the organization constructs. So far, you have only learned about the beginner's examples--examples that do not have any Import, Class or EndClass commands. If you are curious, you can look now at classes and their various methods (Constructor, Routine and Function); otherwise, you may return here later to read about the required command order of these organizational constructs.
- beginner's order rules (short programs)
- Class
- Constructor
- Routine
- Function
- beginner's order rules (short programs)
When writing your first programs, you will not use Import, Class and EndClass commands. These initial programs consists of only two groups:
- Box and Boxes commands (if any)
- action instuctions (have their own ordering requirements)
Note that certain action commands have their own ordering requirements. For example, an EndIf command must come after its matching If command (see command rules above).
- class command order
If your JJ code begins with any Import commands, you are required to have a Class command as the next command and a matching EndClass command as the final command.
Here is a list of the command order requirements for a class:
- Import commands (at least one required)
- Class command (required)
-- Name: yourId goes here(required)-- Does: a description goes here(optional)- Constant commands (if any)
- Box and Boxes commands (if any)
- Constructor method (required)
- Function and Routine methods (if any)
- EndClass command (required)
A class starts with one of two Import commands. A JJ program must either import JJIO (to gain access to Input, Output and Outputln commands) or import JJGui (in gain access to JJ Graphical user interface features such as JJButton and JJGridPanel).
A class starts with a Class command. This is followed with a
-- Name:comments and an optional-- Does:comment. This is followed by Constant commands if you have any. This is followed by Boxes and Box commands (which will need to specifyis publicoris private) if you have any. This is followed by one Constructor method. You must have a constructor, even if it is empty (consists of only the Constructor and the EndConstructor commands). This is followed by any number of Routines and Functions. The class concludes with an EndClass command.- constructor command order
A class is required to have one constructor. The class constructor is called when you create a new object of this class with a New command. (This is a relatively advanced concept. The New command is an action command, it will be in a different class, and it is used to put an object of this class into a (previously) empty box.)
Here is a list of the command order requirements for a constructor:
- Constructor command (required)
- Slot commands (if any)
- Box and Boxes commands (if any)
-- Does: a description goes here(optional)- action commands
- EndConstructor command (required)
A constructor starts with a Constructor command. This is followed by any number of Slot commands. A constructor could accept values passed into slots. If this is the case, you need one slot command for each slot (in which the constructor is expecting a value to be passed into it). These slot commands, if any, are followed by any number of Boxes and Box commands (which are only seen within this constructor, so you do not specify
is publicoris private). This is followed by an optional comment describing what this constructor does. This is followed by any number of action commands. The constructor concludes with an EndConstructor command.
- beginner's order rules (short programs)
- Boxes
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