Kotlin Language Features Related to Null Handling

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Any software engineer with a Java background would find the null handling features in the Kotlin language interesting. Let's summarize this topic with some examples. Nullable types: In Kotlin, types are non-nullable by default. If you want a variable to be able to hold a null value, you need to explicitly declare its type as nullable using the Type? syntax. For example, String? denotes a nullable string, while String represents a non-nullable string. Safe calls (?.): Kotlin introduces the safe call operator (?.) for handling nullable types. It allows you to safely invoke a method or access a property on a nullable object. If the object is null, the expression returns null instead of throwing a NullPointerException. Example: data class Person(val name: String, val age: Int, val address: String?) fun main() {     // Create a person with a nullable address     val person1 = Person("John Doe", 25, "123 Main Street")     val person2 = Person("Jane Doe", 30,...
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A Code Analyzer for a Subset of Java Language (J-) Using ANTLR - PART 1

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Our goal is to write a code analyzer for a language that is called "J minus".

Source code of the whole project can be found here:
https://code.google.com/p/j-minus/

Lets start with the language definition:

Lexical Rules:


Identifiers: Sequence of letters.
Integer literals: A sequence of decimal digits.
Binary operators: && < + - *

Grammar Rules:


Program ->  MainClass ClassDecl*

MainClass ->  class id { public static void main (String [] id) { Statement* }}

ClassDecl ->  class id { VarDecl* MethodDecl* } 

VarDecl ->  Type id ;

MethodDecl -> public Type id ( ( formalParameter (, formalParameter)* )? )
 { varDecl* statement* return exp; } 

FormalParameter ->  Type id

Statement ->  id = Exp;

Exp  ->  AdditionExp | SimpleExp

SimpleExp -> id | int

AdditionExp -> SimpleExp + SimpleExp

Type: 'int' | 'boolean' 
;

We must pass following steps to reach our goal:

1) Implement the lexer and parser for the language. (use ANTLR)
2) Build the Abstract Syntax Tree (AST) using the parser.
3) Create a tree walker for the AST
4) Create and populate a Symbol Table
5) Perform type-checking analysis

-- to be continued

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