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Scala language basics

The Scala language basics summary mind map helps readers comprehensively understand and master the basic concepts and practical skills of the Scala programming language. Whether you are a beginner in programming or an experienced developer, I believe you can get valuable inspiration and gains from this article.

Edited at 2024-11-28 12:53:03

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Scala language basics

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Outline

Scala language basics

Scala language overview

The origin of computers

Lambda calculus is regarded as the smallest general-purpose programming language

programming paradigm

imperative programming

A programming method that executes instructions sequentially

functional programming

A function-based programming paradigm

Introduction to Scala

Scala runs on the Java Virtual Machine and is compatible with existing Java programs

Scala is a pure object-oriented language

Scala is also a functional language

Scala basics

Basic data types and variables

Basic data types

integer type

Byte

Short

Int

Long

string type

String

Boolean type

Boolean

Character type

Char

floating point type

Float

Double

Basic operations

literal

Operator

Arithmetic operators > Relational operators > Logical operators > Assignment operators

Operators are methods in Scala

Rich packaging

Each basic type has a corresponding rich wrapper class

variable

val

Immutable must be initialized when declared

var

variable

I/O

Console input and output statements

Read and write files

control structure

conditional statement

Loop statement

while

for

Exception handling

control over loops

data structure

Array

A mutable, indexable collection of data whose elements are of the same type

Tuple

It is a simple encapsulation of multiple objects of different types.

Container(Collection)

Scala provides a rich set of container libraries, including sequences, collections, mappings, etc.

Sequence

List

An immutable sequence of objects that share the same type

The common way to construct a list is to add elements to the front of an existing list. The operator used is ∷

Once a Scala list is defined, its value cannot be changed. The list must be initialized when declaring it.

Scala also defines an empty list object Ni. With Ni, multiple elements can be connected using the operator "::" to initialize a list.

Vector

All access operations can be implemented in constant time

Range

A special, indexed, immutable arithmetic sequence of numbers

Can support creating numerical sequences of different data types

Set

A container with non-repeating elements that allows you to quickly find an element

Map

A container for a series of key-value pairs

Keys are unique, but values are not necessarily unique

Iterator

It is not a container but a data structure that provides sequential access to the container elements.

Can return the next element of the iterator

hasNext

Used to detect whether there is a next element

Two basic operations

Object-oriented programming basics

kind

Define class

Visibility of class members

public

Public members can be directly accessed from any scope

private

Refers to visible to this type and nested types

protected

Visible to both this type and its inherited types

How methods are defined

Val and var cannot be added before method parameters. All method parameters are immutable types.

The definition of a parameterless method can omit the parentheses

Constructor

The definition body of a Scala class is the constructor of the class, called the main constructor

used to create objects

You can use the val or var keyword before the parameters of the main constructor

Scala will actively create private fields for these parameters internally and provide corresponding access methods.

object

Singleton object

Use object key definition

companion object

When a singleton object appears together with its class of the same name, the singleton object at this time is called a companion object of the class of the same name.

isolated object

There is no singleton object of the same class

The apply method receives the parameters of the constructor and turns them into objects. The unapply method receives an object and extracts the value from it.

inherit

Scala only supports single inheritance, not multiple inheritance

abstract class

Using the keyword abstract, abstract fields in abstract classes must declare types, otherwise compilation errors will occur.

Extended class

Option class

Some

valuable

None

no value

Parameterized types

The definition of a class contains one or several undetermined type parameter information, and its specific type will be determined when the class is instantiated.

Trait

Using "traits" to achieve multiple reuse of code not only realizes the function of the interface, but also has many other features

The characteristic of Scala is that it is the basic unit of code reuse and can have both abstract methods and concrete methods.

A class can only inherit from one superclass, but can implement multiple traits

Traits are similar to abstract classes and can contain both abstract and non-abstract members.

Traits can be mixed into classes using the extends or with keywords

pattern matching

match statement

Used in scenarios where you need to choose from multiple branches

There is no need to use the break statement to jump out of the judgment. When a branch is matched from front to back, the judgment will automatically jump out.

case class

Automatically reload many useful methods

Bag

Different parts of the program can be placed in different packages by adding braces after the keyword Package.

Functional programming basics

higher order function

function as parameter

function returns as result

closure

When a function's immediate dependence depends on one or more variables declared outside the function, the function is called a closure.

Partially applied functions and currying

Generating a new function by retaining some parameters of a known function is called a partial application function

Currying

Operations on containers

Traversal operation

foreach()

Mapping operation

map

one-to-one mapping

flatMap

One-to-many mapping "beat flat"

filter operation

filter

protocol operation

reduce

reduceLeft

reduceRight

fold

foldLeft

foldRight

Perform pairwise operations on container elements