hf-kotlin-griffiths

Practical part of the "Head First Kotlin" book.

Chapter 1. Getting started: A Quick Dip

Key points:

Use fun to define a function.
Every application needs a function named main.
Use // to denote a single-lined comment.
A String is a string of characters. You denote a String value by enclosing its characters in double quotes.
Code blocks are defined by a pair of curly braces { }.
The assignment operator is one equals sign =.
The equals operator uses two equals signs ==.
Use var to define a variable whose value may change.
Use val to define a value whose value will stay the same.
A while loop runs everything within its block so long as the conditional test is true.
If the conditional test is false, the while loop code block won’t run, and execution will move down to the code immediately after the loop block.
Put a conditional test inside parentheses ( ).
Add conditional branches to your code using if and else. The else clause is optional.
You can use if as an expression so that it returns a value. In this case, the else clause is mandatory.

Key points:

In order to create a variable, the compiler needs to know its name, its type, and whether it can be reused.
If the variable’s type isn’t explicitly defined, the compiler infers it from its value.
A variable holds a reference to an object.
An object has state and behavior. Its behavior is exposed through its functions.
Defining the variable with var means the variable’s object reference can be replaced. Defining the variable with val means the variable holds a reference to the same object forever.
Kotlin has a number of basic types: Byte, Short, Int, Long, Float, Double, Boolean, Char and String.
Explicitly define a variable’s type by putting a colon after the variable’s name, followed by the type: var tinyNum: Byte
You can only assign a value to a variable that has a compatible type.
You can convert one numeric type to another. If the value won’t fit into the new type, some precision is lost.
Create an array using the arrayOf function: var myArray = arrayOf(1, 2, 3)
Access an array’s items using, for example, myArray[0]. The first item in an array has an index of 0.
Get an array’s size using myArray.size.
The compiler infers the array’s type from its items. You can explicitly define an array’s type like this: var myArray: Array<Byte>
If you define an array using val, you can still update the items in the array.
String templates provide a quick and easy way of referring to a variable or evaluating an expression from inside a String.

Key points:

Use functions to organize your code and make it more reusable.
A function can have parameters, so you can pass more than one value to it.
The number and type of values you pass to the function must match the order and type of the parameters declared by the function.
A function can return a value. You must define the type of value (if any) it returns.
A Unit return type means that the function doesn’t return anything.
Choose for loops over while loops when you know how many times you want to repeat the loop code.
The readLine() function reads a line of input from the standard input stream. It returns a String value, the text entered by the user.
If the input stream has been redirected to a file and the end of the file has been reached, the readLine() function returns null. null means it has no value, or it’s missing.
&& means “and”. || means “or”. ! means “not”.