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https://github.com/soundlygifted/scriptlanguage

This is an educational console app that executes a script written on a custom script language from an external text file
https://github.com/soundlygifted/scriptlanguage

ant java javacollections javacore javaexceptionhandling javaio javase scripting-language

Last synced: 26 days ago
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This is an educational console app that executes a script written on a custom script language from an external text file

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README 

        
# Script Language Interpreter

### Project description

This Java console app is a script language interpreter that interprets and executes a script written on a custom script language.



### Purpose

The project is made to practice Java Collections, I/O, and other Java SE standard package features.



### Key feature description

The script is loaded from a text file (.txt) and **_executed line by line_**. The name of the file to be loaded is passed either as a command line argument or entered by the user from the keyboard (if there is no argument provided).

The **key features** are:

- perform calculations using whole numbers

- save numbers or calculation results in user-defined variables

- use variables in calculations (resolving variables into numbers stored in the variables)

- print text strings or values of user-defined variables on the screen

- use script documenting comments that are ignored by the script interpreter

- check the script and print errors with the problem description



#### Calculation operations

Calculations are performed in whole numbers. The following operations can be performed:

- addition

- subtraction

- multiplication

- division



The expression for evaluation can contain **opening `(` and closing `)` brackets** to determine the order of operations.



#### Script operators

The user script should contain the following operators (each one on a separate line):

- `set` operator calculates the given expression and assigns result to the named variable. The variable name must start with “`$`” and can include Latin letters, numbers and underscore mark only. The expression must be a number, other variable or must consist of numbers, other variable(s) and calculation operations named above

- `print` operator prints the specified list of strings and variables to the screen: strings and variables in the list are separated by commas; strings are enclosed in double quotes

- `#` operator determines a comment. Any line that starts with `#` will be ignored

- blank lines are ignored



### Usage example

The demo script file can be found in the root directory of the project (**DemoScript.txt**). It contains the following script.

```

# Printing some string

print "Hi, Alexey!"



# Performing "set" operations

set $n1 = 21

set $n2 = 121

set $sum = ($n1 - ($n2 - 42)) * (4 - 42 / $n1)



# Printing the script

print

print "You entered this script:"

print "set $n1 = ", $n1

print "set $n2 = ", $n2

print "$sum = ", "($n1 - ($n2 - 42)) * (4 - 42 / $n1) = ", $sum

```

The user passes the file name as a command line argument when launching the jar-file, or enters it from the keyboard after the corresponding request from the program (if the argument was not entered). The program displays the following result on the screen:

```

Hi, Alexey!



You entered this script:

set $n1 = 21

set $n2 = 121

$sum = ($n1 - ($n2 - 42)) * (4 - 42 / $n1) = -116



[ScriptLanguage] Program finished running. Press Enter to finish...

```

After the user presses Enter, the program will exit.

### Project structure

This is a simple Ant-based Java application. The diagram of modules and classes is shown in the figure below.



![](images/ScriptLanguage_Classes.PNG)



- `main` package contains `ScriptLanguage.java` class which is the main Application class. It addresses to the classes of the underlying packages (to read and interpret a script) and handles the incoming exceptions

  - `main.io` package contains classes that read external data from different sources

    - `KeyboardInputReader.java` class reads user keyboard input (e.g., when user inputs script file name)

    - `ScriptReader.java` class reads script file for further script interpretation / execution

    - `main.io.exceptions` package contains custom exception class (`FileReadingException.java`) that is used to throw exceptions connected with I/O operations

  - `main.process` package contains classes for the script interpretation which includes script parsing and validation, as well as performing related calculations and processing

    - `ScriptInterpreter.java` class is designed to interpret the script and return the final result. It addresses to other classes contained in the sub-packages of `main.process` package to perform the job.

    - `main.process.operations` package contains classes each one of which performs a separate script operation

      - `OperationPeformer.java` is an abstract class that represents performance of an abstract operation

      - `PrintOperationPerformer.java` class extends `OperationPeformer.java` class. It is designed to perform `print` script operation

      - `SetOperationPerformer.java` class extends `OperationPeformer.java` class. It is designed to perform `set` script operation

    - `main.process.exceptions` package contains custom exception classes (`UnsupportedScriptOperationException.java`, `WrongScriptExpressionExeption.java`) that are used to throw exceptions connected with the script interpretation and execution