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\author{Bochrak}
\pdfinfo{
  /Title (kotlin-fundamentals-for-android-development.pdf)
  /Creator (Cheatography)
  /Author (Bochrak)
  /Subject (Kotlin Fundamentals for Android Development Cheat Sheet)
}

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    {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent
        \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}}
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    \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{Kotlin Fundamentals for Android Development Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{Bochrak} via \textcolor{DarkBackground}{\uline{cheatography.com/200241/cs/46213/}}}
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  \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}}  \\
  \vspace{-2pt}Bochrak \\
  \uline{cheatography.com/bochrak} \\
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  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Not Yet Published.\\
   Updated 27th April, 2025.\\
   Page {\thepage} of \pageref{LastPage}.
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  %\includegraphics[width=48px,height=48px]{dave.jpeg}
  Measure your website readability!\\
  www.readability-score.com
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\begin{multicols*}{2}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Kotlin}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{Kotlin is a {\bf{modern}}, {\bf{statically-typed programming language}} that runs on the {\bf{Java Virtual Machine (JVM)}} and can also be compiled to {\bf{JavaScript}} or {\bf{native code}}.\{\{nl\}\} \{\{fa-info-circle\}\} Developed by {\bf{JetBrains}} (the makers of IntelliJ IDEA) \{\{nl\}\} \{\{fa-info-circle\}\} Officially supported for {\bf{Android app development}} by {\bf{Google}} 2017 \{\{nl\}\} \{\{fa-info-circle\}\} Designed to be {\bf{concise}}, {\bf{safe}} and {\bf{interoperable with Java}}% Row Count 10 (+ 10)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
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\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Key Features}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-check-circle\}\} Concise syntax \{\{nl\}\} \{\{fa-check-circle\}\} Null Safety built-in \{\{nl\}\} \{\{fa-check-circle\}\} Fully interoperable with Java \{\{nl\}\} \{\{fa-check-circle\}\} Coroutines for lightweight concurrency \{\{nl\}\} \{\{fa-check-circle\}\} Multi-platform support (JVM, Android, Web, Native)% Row Count 6 (+ 6)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Variables}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-circle-right\}\} {\bf{var :}}  {\emph{Mutable}} reference. The value can change during runtime. Its value can be reassigned after declaration. \{\{nl\}\}\{\{fa-chevron-circle-right\}\} {\bf{val :}} {\emph{Immutable}} reference. You cannot reassign a value once assigned. Read-only variables. \{\{nl\}\}\{\{nl\}\} \{\{fa-code\}\} {\bf{Immutable variables (val) - values cannot change}} \{\{nl\}\}`val drinkCount: Int`  // ✅ Must specify Type since no initializer \{\{nl\}\} `drinkCount = 12 `   // ✅ Assigned later before usage \{\{nl\}\} `println(drinkCount)`             // Output: 12 \{\{nl\}\} `drinkCount = 15`  // ❌ Error: Val cannot be reassigned \{\{nl\}\}`val popcornBoxes = 5`  // ✅ Kotlin infers Int type \{\{nl\}\}`val hotdogCount: Int = 7` // ✅ Explicitly declared as Int \{\{nl\}\} \{\{fa-code\}\} {\bf{Mutable variable (var) - value can change}} \{\{nl\}\}`var x = 5`  // Mutable variable \{\{nl\}\}  `x += 1`  // ✅ Increments x by 1\{\{nl\}\} `println(x)`  // Output: 6% Row Count 19 (+ 19)
} \tn 
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\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{lateinit}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\} Allows initializing a non-null variable later\{\{nl\}\} \{\{fa-chevron-up\}\} Used when you cannot initialize a variable at the time of declaration, often for classes or Android views.\{\{nl\}\} \{\{fa-exclamation-triangle\}\} Must be a var (NOT val) \{\{nl\}\} \{\{fa-exclamation-triangle\}\} Must be a non-primitive type (no Int, Double, etc.) \{\{nl\}\} \{\{fa-exclamation-triangle\}\} Must be initialized before use\{\{nl\}\}\{\{nl\}\}  \{\{fa-code\}\} {\bf{Basic Syntax}} \newline % Row Count 9 (+ 9)
`lateinit var variableName: Type` \{\{nl\}\} \{\{fa-code\}\} `lateinit var count: Int` // ❌ Compile-time error \{\{nl\}\} \{\{fa-code\}\} `lateinit var count: String` // ✅ Valid% Row Count 13 (+ 4)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Nullable types}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\} A nullable type means a variable can hold a null value. \{\{nl\}\} \{\{fa-chevron-up\}\}  Enhances null safety, reducing runtime crashes due to NullPointerException (NPE) from Java.\{\{nl\}\}  \{\{fa-exclamation-triangle\}\} Must explicitly allow a variable to be null by adding {\bf{?}} to its type.\{\{nl\}\} \{\{nl\}\} \{\{fa-code\}\} `var studentName: String? = "Sarah" ` \{\{nl\}\} `studentName = null` // ✅  Allowed because of the "?" in String? \{\{nl\}\} \{\{fa-code\}\} `var teacherName: String = "John" `\{\{nl\}\}`teacherName = null` // ❌ Error: Null can not be a value of a ~	nonnull type String% Row Count 12 (+ 12)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Safe Call}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\}  {\bf{The Safe Call Operator ?.}} allows you to {\bf{safely access}} properties or methods {\bf{only if the variable is NOT null}}. \{\{nl\}\}\{\{fa-chevron-up\}\} If the variable is {\bf{null}}, the call{\bf{ returns null}} instead of throwing a crash. \{\{nl\}\}\{\{nl\}\} \{\{fa-code\}\} {\bf{Basic Syntax}} \newline % Row Count 6 (+ 6)
` \seqsplit{nullableVariable?.methodOrProperty} ` \{\{nl\}\}\{\{fa-code\}\} `var name: String? = "Sarah"` \{\{nl\}\} `println(name?.length)` // Output: 5 \{\{nl\}\} `name = null`  \{\{nl\}\}`println(name?.length)` // Output: null (no crash!) \{\{nl\}\}\{\{fa-code\}\} \seqsplit{`student?.school?.address?.city`} // Chain safe calls. Each ?. checks at every level safely% Row Count 13 (+ 7)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Elvis operator}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\}  {\bf{The Elvis Operator ?: }} is used to {\bf{provide a default value}} when an expression on the left is {\bf{null}}. \{\{nl\}\} \{\{fa-chevron-up\}\}  If the left side is {\bf{not null}}, it returns the left side.\{\{nl\}\} \{\{fa-chevron-up\}\} If the left side is {\bf{null}}, it returns the right side (the default). \{\{nl\}\}\{\{nl\}\} \{\{fa-code\}\} {\bf{Basic Syntax}} \newline % Row Count 8 (+ 8)
`val result = nullableVariable ?: defaultValue`\{\{nl\}\} \{\{fa-code\}\} `var name: String? = "Sarah"` \{\{nl\}\}  `val finalName = name ?: "Unknown" ` \{\{nl\}\} `println(finalName)` // Output: Sarah \{\{nl\}\}\{\{fa-code\}\} `var name: String? = null `\{\{nl\}\}  `val finalName = name ?: "Unknown"` \{\{nl\}\} `println(finalName) `// Output: Unknown% Row Count 15 (+ 7)
} \tn 
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Classes}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\}  A {\bf{class}} is a {\bf{blueprint}} for creating objects (instances) with {\bf{properties}} and {\bf{functions}} (methods). \newline % Row Count 3 (+ 3)
\{\{nl\}\} \{\{fa-code\}\} {\bf{Basic Syntax}} \newline % Row Count 4 (+ 1)
`class User (` \newline % Row Count 5 (+ 1)
 `var firstName: String,` \newline % Row Count 6 (+ 1)
 `var lastName: String,` \newline % Row Count 7 (+ 1)
 `var address: String? = null` \newline % Row Count 8 (+ 1)
`)` \newline % Row Count 9 (+ 1)
\{\{fa-code\}\} `class Car(val brand: String, var speed: Int) \{` \newline % Row Count 11 (+ 2)
    `fun drive() \{` \newline % Row Count 12 (+ 1)
       ` println("Driving \$brand at \$speed km/h")` \newline % Row Count 14 (+ 2)
   ` \}` \newline % Row Count 15 (+ 1)
`\}` \newline % Row Count 16 (+ 1)
\{\{fa-code\}\} `val myCar = Car("Toyota", 120)` \newline % Row Count 17 (+ 1)
`myCar.drive()` // Output: Driving Toyota at 120 km/h% Row Count 19 (+ 2)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Data classes}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\}  A {\bf{Data Class}} is a special class designed to {\bf{hold data}}. \newline % Row Count 2 (+ 2)
\{\{fa-chevron-up\}\}  To declare a data class, use the keyword {\bf{data}}. \newline % Row Count 4 (+ 2)
\{\{fa-chevron-up\}\} Kotlin {\bf{automatically generates}} useful {\bf{methods}} for you: toString() \newline % Row Count 6 (+ 2)
equals(), hashCode(), copy()... \newline % Row Count 7 (+ 1)
\{\{nl\}\} \{\{fa-code\}\} {\bf{Basic Syntax}} \newline % Row Count 8 (+ 1)
`data class ClassName(val prop1: Type, val prop2: Type)` \newline % Row Count 10 (+ 2)
\{\{fa-code\}\} `data class User(val name: String, val age: Int)` \newline % Row Count 12 (+ 2)
`val u = User("Sarah", 25)` \newline % Row Count 13 (+ 1)
`println(u)` // Output: User(name=Sarah, age=25) \newline % Row Count 14 (+ 1)
`val u2 = u.copy(age = 26)` \newline % Row Count 15 (+ 1)
`println(u2)` \newline % Row Count 16 (+ 1)
 // Output: User(name=Sarah, age=26)% Row Count 17 (+ 1)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-exclamation-triangle\}\} Must have at least one property inside primary constructor. \newline \{\{fa-exclamation-triangle\}\} Properties should be val or var Otherwise not allowed.}  \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Collections}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\} {\bf{Groups of related elements}} you can store, manage, and manipulate together. \{\{nl\}\} \{\{fa-chevron-circle-right\}\} {\bf{List:}} Ordered collection, allows duplicates. {\bf{listOf(1, 2, 2, 3)}}\{\{nl\}\} \{\{fa-chevron-circle-right\}\} {\bf{Set:}} Unordered, unique elements. {\bf{setOf(1, 2, 3)}}\{\{nl\}\} \{\{fa-chevron-circle-right\}\} {\bf{Map:}} Key-value pairs. {\bf{mapOf("name" to "Sarah")}}\{\{nl\}\}\{\{nl\}\}  🟢 {\bf{Mutable Collections:}} Collections that allow modifications (add/remove/update) after creation. Useful when the data structure needs to change dynamically.\{\{nl\}\} ✅ {\bf{mutableListOf, mutableMapOf, mutableSetOf()}}\{\{nl\}\}\{\{nl\}\}  \{\{fa-code\}\} {\bf{Mutable list with explicit type declaration}}\{\{nl\}\} `val shapes: MutableList\textless{}String\textgreater{} = mutableListOf("tri", "squ")`\{\{nl\}\} `shapes.add("cir")`\{\{nl\}\} `println(shapes)` // {[}tri, squ, cir{]}\{\{nl\}\}\{\{nl\}\}  🔴 {\bf{Immutable Collections:}} Immutable collections that cannot be modified after creation. They provide safety by ensuring your data remains unchanged.\{\{nl\}\} ⭕ {\bf{listOf, mapOf, emptyListOf, emptyMapOf}}\{\{nl\}\}\{\{nl\}\}  \{\{fa-code\}\} {\bf{Read-only list}}\{\{nl\}\} `val readOnlyShapes = listOf("triangle", "square")`\{\{nl\}\} \seqsplit{`println(readOnlyShapes)`} // {[}triangle, square{]}\{\{nl\}\} `println("First item is: \$\{readOnlyShapes{[}0{]}\}")` // triangle \{\{nl\}\} \{\{nl\}\}% Row Count 26 (+ 26)
} \tn 
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\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Common Collection Operations}}  \tn
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{\bf{Add}} & fruits.add("Mango") \tn 
% Row Count 1 (+ 1)
% Row 1
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{\bf{Remove}} & fruits.remove("Banana") \tn 
% Row Count 2 (+ 1)
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{\bf{Loop List}} & for (item in list) \{\} \tn 
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\SetRowColor{white}
{\bf{Loop Map}} & for ((k,v) in map) \{\} \tn 
% Row Count 4 (+ 1)
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{\bf{Contains}} & list.contains(2) \tn 
% Row Count 5 (+ 1)
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{\bf{Size}} & list.size \tn 
% Row Count 6 (+ 1)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Conditional expressions}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\} In Kotlin, many control structures like if, when are {\bf{expressions}}, {\bf{they return a value}} (not just perform actions like in Java or C++).  \newline % Row Count 4 (+ 4)
\{\{fa-chevron-up\}\}You can assign the result of an if or when directly to a variable! \newline % Row Count 6 (+ 2)
\{\{fa-arrow-circle-right\}\} {\bf{if :}}  \newline % Row Count 7 (+ 1)
\{\{fa-code\}\} `val max = if (a \textgreater{} b) a else b` // if (a \textgreater{} b) returns a, otherwise b, and assigns the result to max. No need to create extra variables manually. \newline % Row Count 11 (+ 4)
There is {\bf{no ternary operator}} condition ? then : else in Kotlin. \newline % Row Count 13 (+ 2)
\{\{fa-arrow-circle-right\}\} {\bf{when :}}  \newline % Row Count 14 (+ 1)
\{\{fa-code\}\} `val result = when (score) \{` \newline % Row Count 15 (+ 1)
   ` in 90..100 -\textgreater{} "Excellent"` \newline % Row Count 16 (+ 1)
   ` in 75..89 -\textgreater{} "Good"` \newline % Row Count 17 (+ 1)
   ` in 60..74 -\textgreater{} "Pass"` \newline % Row Count 18 (+ 1)
   ` else -\textgreater{} "Fail"` \newline % Row Count 19 (+ 1)
\}  // All branch conditions are checked sequentially until one of them is satisfied. So only the first suitable branch is executed.% Row Count 22 (+ 3)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Loops}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-circle-right\}\} {\bf{for :}} Iterate over a range of values,array, list, etc and perform an action. \newline % Row Count 3 (+ 3)
\{\{fa-code\}\}  {\bf{Iterating a list}} \newline % Row Count 4 (+ 1)
`val fruits = listOf("Apple", "Banana", "Cherry")` \newline % Row Count 6 (+ 2)
`for (fruit in fruits) \{` \newline % Row Count 7 (+ 1)
`    println(fruit) \}` \newline % Row Count 8 (+ 1)
\{\{fa-code\}\} {\bf{Iterating a range}} \newline % Row Count 9 (+ 1)
`for (i in 1..5) \{` \newline % Row Count 10 (+ 1)
    `println(i)` // Prints 1 2 3 4 5`\}` \newline % Row Count 11 (+ 1)
\{\{fa-chevron-circle-right\}\} {\bf{While :}} To execute a code block while a conditional expression is true. \newline % Row Count 14 (+ 3)
\{\{fa-code\}\} `var x = 5` \newline % Row Count 15 (+ 1)
`while (x \textgreater{} 0) \{` \newline % Row Count 16 (+ 1)
    `println(x)` \newline % Row Count 17 (+ 1)
   ` x-{}- \}` // Repeats while x \textgreater{} 0. \newline % Row Count 18 (+ 1)
\{\{fa-chevron-circle-right\}\} {\bf{do...while :}} To execute the code block first and then check the conditional expression. \newline % Row Count 21 (+ 3)
\{\{fa-code\}\} `var y = 0` \newline % Row Count 22 (+ 1)
`do \{` \newline % Row Count 23 (+ 1)
    `println(y)` \newline % Row Count 24 (+ 1)
    `y++` \newline % Row Count 25 (+ 1)
`\} while (y \textless{} 3)` //  Runs at least once, even if condition is false after first execution.% Row Count 27 (+ 2)
} \tn 
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\begin{tabularx}{8.4cm}{X}
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\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Functions}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\}  A function groups reusable code.  \newline % Row Count 2 (+ 2)
\{\{fa-chevron-up\}\} Can be defined in a class (method) or directly in a package. \newline % Row Count 4 (+ 2)
\{\{fa-chevron-up\}\} You can declare your own functions in Kotlin using {\bf{fun}} keyword. \newline % Row Count 6 (+ 2)
\{\{nl\}\} \{\{fa-code\}\} Basic Syntax \newline % Row Count 7 (+ 1)
`fun functionName(param1: Type, param2: Type): ReturnType`  \newline % Row Count 9 (+ 2)
`\{` \newline % Row Count 10 (+ 1)
    // function body \newline % Row Count 11 (+ 1)
`\} ` \newline % Row Count 12 (+ 1)
\{\{fa-code\}\} `fun add(a: Int, b: Int): Int \{` \newline % Row Count 13 (+ 1)
    `return a + b` \newline % Row Count 14 (+ 1)
`\}` // add(2, 3) returns 5. \newline % Row Count 15 (+ 1)
\{\{fa-code\}\} `fun multiply(a: Int, b: Int) = a * b`  \newline % Row Count 17 (+ 2)
// No \{\} or return needed if it's one expression.% Row Count 18 (+ 1)
} \tn 
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\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Lambda expressions}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{fa-chevron-up\}\}  A {\bf{Lambda}} is an {\bf{anonymous function}}, a "function literal". \newline % Row Count 2 (+ 2)
\{\{fa-chevron-up\}\} A function that is not declared, but passed immediately as an expression.  \newline % Row Count 4 (+ 2)
\{\{fa-chevron-up\}\} {\bf{Lambda expressions}} can be assigned to variables, passed as \newline % Row Count 6 (+ 2)
arguments, or returned from functions.  \newline % Row Count 7 (+ 1)
\{\{nl\}\}\{\{fa-code\}\} {\bf{Basic Syntax}} \newline % Row Count 8 (+ 1)
\{ `parameter1: Type, parameter2: Type -\textgreater{} body `\} \newline % Row Count 9 (+ 1)
//  \{\} : Lambda block \newline % Row Count 10 (+ 1)
// -\textgreater{} : Separates parameters from body \newline % Row Count 11 (+ 1)
\{\{fa-code\}\} {\bf{Simple Lambda}} \newline % Row Count 12 (+ 1)
`val greet = \{ println("Hello, World!") \}` \newline % Row Count 13 (+ 1)
`greet()` // Prints "Hello, World!" \newline % Row Count 14 (+ 1)
\{\{fa-code\}\} {\bf{Lambda with parameters}} \newline % Row Count 15 (+ 1)
`val add = \{ a: Int, b: Int -\textgreater{} a + b \}` \newline % Row Count 16 (+ 1)
`println(add(3, 5))` // Output: 8 \newline % Row Count 17 (+ 1)
\{\{fa-code\}\} {\bf{Lambda passed to a function}} \newline % Row Count 18 (+ 1)
`fun calc(a: Int, b: Int, op: (Int, Int) -\textgreater{} Int): Int \{` \newline % Row Count 20 (+ 2)
    `return op(a, b)` \newline % Row Count 21 (+ 1)
\}` \newline % Row Count 22 (+ 1)
`val res = calc(2, 3) \{ x, y -\textgreater{} x * y \}; println(res)`  \newline % Row Count 24 (+ 2)
// 6% Row Count 25 (+ 1)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{8.4cm}}{{\bf{it keyword :}} When there's only one parameter, it is used automatically. \newline \{\{fa-code\}\} `val square: (Int) -\textgreater{} Int = \{ it * it \} ` \newline `println(square(4))` // Output: 16. No need to name the parameter explicitly if there's only one.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}


% That's all folks
\end{multicols*}

\end{document}