Download to read offline
Compose #1.pptx
- 1. This work islicensed under the Apache 2.0 License Kotlin Fundamentals
- 2. This work islicensed under the Apache 2.0 License Compose apps are written in the Kotlin programming language. Kotlin is the language that the majority of professional Android developers use to build apps.
- 3. This work islicensed under the Apache 2.0 License Kotlin Playground Write and run Kotlin code in the browser. https://play.kotlinlang.org/
- 4. This work islicensed under the Apache 2.0 License Program A series of instructions for a computer to perform some action. fun main() { println("Hello, world!") } Output: Hello, world!
- 5. Functions A function isa segment of a program that performs a specific task. You can have many functions in your program
- 6. This work islicensed under the Apache 2.0 License main Function The main function is the entry point, or starting point, of the program. Start here fun main() { println("Hello, world!") } Output: Hello, world!
- 7. This work islicensed under the Apache 2.0 License Defining a function Functions begin with the fun keyword. fun displayIntroduction() { }
- 8. This work islicensed under the Apache 2.0 License Defining a function Functions have a name so that they can be called. fun displayIntroduction() { }
- 9. This work islicensed under the Apache 2.0 License Defining a function Functions need a set of parentheses after the function name in order to surround the function inputs or parameters. fun displayIntroduction() { }
- 10. This work islicensed under the Apache 2.0 License Defining a function The curly braces make up the function body and contain the instructions needed to execute a task. fun displayIntroduction() { // Body }
- 11. This work islicensed under the Apache 2.0 License Putting it together fun main() { firstFunction() // Call a function } // Define a function fun firstFunction() { // Function Body }
- 12. This work islicensed under the Apache 2.0 License Basic data types Kotlin Data type What kind of data it can contain Example literal values String Text “Add contact” “Search” Int Whole integer number 32 -59873 Double Decimal number 2.0 -37123.9999 Float Decimal number (less precise than a Double). Has an f or F at the end of the number. 5.0f -1630.209f Boolean true or false. Use this data type when there are only two possible values. true false
- 13. This work islicensed under the Apache 2.0 License A container for a single piece of data. Variables
- 14. This work islicensed under the Apache 2.0 License val keyword Use when you expect the variable value will not change. Example: name var keyword Use when you expect the variable value can change. Example: age Defining a variable
- 15. This work islicensed under the Apache 2.0 License Defining a variable Variables start with a var or val keyword. fun main() { val name: String = "Bhavye" var age: Int = 20 }
- 16. This work islicensed under the Apache 2.0 License Defining a variable All variables must have a name. fun main() { val name: String = "Meghan" var age: Int = 28 }
- 17. This work islicensed under the Apache 2.0 License Defining a variable Data type is the type of data that the variable holds. fun main() { val name: String = "Meghan" var age: Int = 28 }
- 18. This work islicensed under the Apache 2.0 License Defining a variable The initial value is the value that is stored in the variable. fun main() { val name: String = "Meghan" var age: Int = 28 // val name = “Meghan” // var age = 28 }
- 19. This work islicensed under the Apache 2.0 License Defining a variable If we want to define a variable with no initial value. fun main() { val name: String var age: Int // var age => Error }
Editor's Notes
- #4 To make it easier for you to learn, you’ll be writing your code in the Kotlin Playground which you can access via the web browser. The site looks something like this. You can write your code in this window and run it by hitting the green Run button. The result of your code (known as the output) will show up at the bottom of the window (where it says “Hello, world!”). To illustrate a few important concepts that you’ll learn in this pathway, we will go through a short code demo to create a program in Kotlin.
- #5 In Kotlin Playground, you will learn to explore and modify simple programs in Kotlin. You can think of a program as a series of instructions for a computer or mobile device to perform some action. In this program, the action is printing “Hello, world!”.
- #6 A function is a segment of a program that performs a specific task. You can have many functions in your program or only a single one. Creating separate functions for specific tasks has a number of benefits. Reusable code: Rather than copying and pasting code that you need to use more than once, you can simply call a function wherever needed. Readability: Ensuring functions do one and only one specific task helps other developers and teammates, as well as your future self to know exactly what a piece of code does.
- #7 A Kotlin program is required to have a main function, which is the entry point, or starting point, of the program. You may be asking what a function is…
- #8 We will demonstrate how to define a function with a function called displayIntroduction() that we will use to print our name and age. A function definition starts with the fun keyword. A keyword is a reserved word that has a special meaning in Kotlin, in this case the fun keyword tells Kotlin that you are going to make a function.
- #9 Functions need to have a descriptive name so that they can be called from other parts of the program.
- #10 Functions need a set of parentheses which you can use to optionally pass information into the function. displayIntroduction() won’t need information passed in. You will learn more about passing in inputs into functions later in the course.
- #11 Functions need curly braces that contain the instructions needed to execute a task.
- #12 Finally, we will replace the contents of the main() function with a call to the displayIntroduction() function when we run it, “Hi I’m Meghan and I am 28 years old” will print to the output. In this lecture we went over functions and variables and how to put them together to create a function that introduces you. Soon you will go deeper into these concepts and try them out for yourself in the codelabs.
- #13 When you decide what aspects of your app can be variables, it's important to specify what type of data can be stored in those variables. In Kotlin, there are some common basic data types. This table shows a different data type in each row. For each data type, there's a description of what kind of data it can hold and example values. A String holds text so you will use it to store your name, and an Int holds an integer number so you will use it to store your age.
- #14 In computer programming, a variable is a container for a single piece of data. You can envision it as a box that contains a value. The box has a label, which is the name of the variable. By referring to the box by its name, you have access to the value it holds.
- #15 Now, let’s jump into how you define a variable. You can declare a variable using either val or var. With val, the variable is read-only, which means you can only read, or access, the value of the variable. Once the value is set, you cannot edit or modify its value. With var, the variable is mutable, which means the value can be changed or modified. The value can be mutated. In Kotlin, it's preferred to use val over var when possible. We will store your name as a val because that will not change. We will store your age as a var because it changes every year.
- #16 To demonstrate how to define a variable we will define both name and age variables. Before you use a variable, you must declare it. To declare a variable, start with the val or var keyword.
- #17 All variables must have a name that they can be referenced by.
- #18 The data type specifies the type of data that the variable holds. Note that a colon separates the name and data type.
- #19 In the variable declaration, the equal sign symbol (=) follows the data type. The equal sign symbol is called the assignment operator. The assignment operator assigns a value to the variable. The variable’s initial value is the data stored in the variable.
- #20 In the variable declaration, the equal sign symbol (=) follows the data type. The equal sign symbol is called the assignment operator. The assignment operator assigns a value to the variable. The variable’s initial value is the data stored in the variable.