Android development with Kotlin programming language - basic data types

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I. Introduction

Kotlin: A programming language widely used by Android developers around the world

Second, variable declaration

1. Kotlin uses two different keywords

• val : for variables whose value never changes.Variables declared with val cannot be reassigned.
• var : for variables whose value can be changed.

2. Examples

//num is a variable of type Int, the initial value is 10var num: Int = 10//The value of num can be changed from 10 to 15num=15

Int is a type that represents integers and is one of many numeric types that can be represented in Kotlin.Similar to other languages, you can also use Byte, Short, Long, Float, and Double, depending on your numeric data.

• Assume there is a String named name.If you want to ensure that the value of name is always "Kotlin", you can declare name using the val keyword:

val name: String = "Kotlin"

These keywords allow you to specify which variables can have their values ​​changed.Please use it as needed.If the referenced variable must be reassignable, declare it as var.Otherwise, use val.

Third, type inference

val name= "Kotlin"

Since the value of "Kotlin" is of type String, the compiler infers that name is also String.Note that Kotlin is a statically typed language.This means, the type will be resolved at compile time and will never change.

Using Kotlin's type inference to ensure code simplicity and type safety

Four. Null Safety

In some languages, it is possible to declare a reference type variable without explicitly providing an initial value.In such cases, the variable usually contains a null value.By default, Kotlin variables cannot hold null values.This means that the following code snippet is invalid:

val name:String= null

• For a variable to hold a null value, it must be of a nullable type.You can designate a variable as nullable by suffixing the variable type with a ?, as shown in the following example:

val name:String? = null

• After specifying the String? type, you can assign a String value or null to name.

Nullable variables must be handled with care or the dreaded NullPointerException may occur.For example, in Java, if you try to call a method on a null value, the program will crash.