# Scala導入ティップス
**URL:** https://forum.ficusonline.com/t/topic/385
**Category:** Programming
**Created:** [2020 年 10 月 3 日午後 2:15 UTC](https://forum.ficusonline.com/t/topic/385 "2020-10-03T14:15:15Z")
**Posts on this page:** 11
**Page:** 2
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 26 日午前 8:42 UTC](https://forum.ficusonline.com/t/topic/385/21 "2020-10-26T08:42:09Z")
### ABSTRACT CLASSES
**Trait** ではパラメータを定義できないため、パラメータを定義できる **Trait** として利用。
**Java** コードから呼び出す際にも使用。
拡張クラスは、 **abstract class** を一つだけしか利用できない。
> **[Abstract Classes](https://docs.scala-lang.org/overviews/scala-book/abstract-classes.html)**
>
> This page shows how to use abstract classes, including when and why you should use abstract classes.
以下 **Trait** では変数を定義できない。
```auto
trait Animal(name: String) --->コンパイルエラー
```
**abstract class** により変数を定義。
```auto
abstract class Animal(name: String)
```
**Ex) Pet(name)** が **abstract class** であることを示す。
```auto
abstract class Pet (name: String) {
def speak: Unit = println(s"My name is $name")
}
class Dog(name: String) extends Pet(name)
val d = new Dog("Fido")
d.speak
```
クラスメンバーに **abstract type** を含む場合（具体的な値やメソッドが定義されていない）にも **abstract class** を使用。
> **[Abstract Classes in Scala - GeeksforGeeks](https://www.geeksforgeeks.org/scala/abstract-classes-in-scala/)**
>
> Your All-in-One Learning Portal: GeeksforGeeks is a comprehensive educational platform that empowers learners across domains-spanning computer science and programming, school education, upskilling, commerce, software tools, competitive exams, and...
```java
// Scala program to illustrate how to
// create an abstract class
// Abstract class
abstract class myauthor
{
// abstract method
def details()
}
// GFG class extends abstract class
class GFG extends myauthor
{
def details()
{
println("Author name: Ankita Saini")
println("Topic name: Abstract class in Scala")
}
}
object Main
{
// Main method
def main(args: Array[String])
{
// objects of GFG class
var obj = new GFG()
obj.details()
}
}
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 26 日午後 3:07 UTC](https://forum.ficusonline.com/t/topic/385/22 "2020-10-26T15:07:13Z")
### ABSTRACT TYPE MEMBERS
具体的な型のタイプ、値、メソッドなどを定義していないクラスメンバー
> **[Abstract Type Members](https://docs.scala-lang.org/tour/abstract-type-members.html)**
> **[Scala | Abstract Type members - GeeksforGeeks](https://www.geeksforgeeks.org/scala/scala-abstract-type-members/)**
>
> Your All-in-One Learning Portal: GeeksforGeeks is a comprehensive educational platform that empowers learners across domains-spanning computer science and programming, school education, upskilling, commerce, software tools, competitive exams, and...
```java
// Scala program of abstract type member
// Declaring an abstract class
abstract class vehicle (name:String)
{
// This is an abstract member
// with undefined implementation
val category: String
// A function that is used to print
// the value of the abstract member
def car_type{ println(category) }
override def toString = s" The vehicle type is $category"
}
// Now extend the classes bike, car,
// truck and bus and provide values
// for the variable type
class car (name:String) extends vehicle (name)
{
// assigning the value of
// the abstract member as car
val category = "car"
}
class bike (name:String) extends vehicle (name)
{
// assigning the value of
// the abstract member as bike
val category = "bike"
}
class bus (name:String) extends vehicle (name)
{
// assigning the value of
// the abstract member as bus
val category = "bus"
}
class truck (name:String) extends vehicle (name)
{
// assigning the value of
// the abstract member as truck
val category = "truck"
}
object AbstractFieldsDemo extends App
{
// assigning the name as Honda in the abstract
// class where the category value is car
val car = new car("Honda")
// assigning the name as Yamaha in the abstract
// class where the category value is bike
val bike = new bike("Yamaha")
// assigning the name as Tata in the abstract
// class where the category value is bus
val bus = new bus("Tata")
// assigning the name as Ashok_Leyland in the
// abstract class where the category value is truck
val truck = new truck("Ashok_Leyland")
// implementing the function
// car_type for the object car
car.car_type
// implementing the function
// car_type for the object bus
bus.car_type
// implementing the function
// car_type for the object truck
truck.car_type
// implementing the function
// car_type for the object bus
bike.car_type
println(car)
println(bus)
println(truck)
println(bike)
}
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 27 日午前 9:05 UTC](https://forum.ficusonline.com/t/topic/385/23 "2020-10-27T09:05:09Z")
### Keywords/reserved symbols
> **[Redirecting…](https://docs.scala-lang.org/tutorials/FAQ/finding-symbols.html)**
```
// Keywords
<- // Used on for-comprehensions, to separate pattern from generator
=> // Used for function types, function literals and import renaming
// Reserved
( ) // Delimit expressions and parameters
[] // Delimit type parameters
{ } // Delimit blocks
. // Method call and path separator
// /* */ // Comments
# // Used in type notations
: // Type ascription or context bounds
<: >: // Upper and lower bounds
<% // View bounds (deprecated)
" """ // Strings
' // Indicate symbols and characters
@ // Annotations and variable binding on pattern matching
` // Denote constant or enable arbitrary identifiers
, // Parameter separator
; // Statement separator
_* // vararg expansion
_ // Many different meanings
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 30 日午前 7:17 UTC](https://forum.ficusonline.com/t/topic/385/24 "2020-10-30T07:17:26Z")
### MODIFIERS
Method modifiers should be given in the following order (when each is applicable):
Annotations, each on their own line
Override modifier ( **override** )
Access modifier ( **protected, private** )
Implicit modifier ( **implicit** )
Final modifier ( **final** )
```auto
def
@Transaction
@throws(classOf[IOException])
override protected final def foo(): Unit = {
...
}
```
## Override
サブクラスによる元クラスの内容（メソッド）を上書き（変数の定義は不変）
> **[Method Overriding in Scala - GeeksforGeeks](https://www.geeksforgeeks.org/scala/method-overriding-in-scala/)**
>
> Your All-in-One Learning Portal: GeeksforGeeks is a comprehensive educational platform that empowers learners across domains-spanning computer science and programming, school education, upskilling, commerce, software tools, competitive exams, and...
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 30 日午後 2:35 UTC](https://forum.ficusonline.com/t/topic/385/25 "2020-10-30T14:35:38Z")
## Self Reference(this)
On the inside of a class, the name **this** represents the object on which the current method is executed.
Add the functions less and max to the class Rational.
```auto
class Rational(x: Int, y: Int) {
...
def less(that: Rational) =
numer * that.denom < that.numer * denom
def max(that: Rational) =
if (this.less(that)) that else this
}
```
Note that a simple name x, which refers to another member of the class, is an abbreviation of **this.x**. Thus, an equivalent way to formulate less is as follows.
```auto
def less(that: Rational) =
this.numer * that.denom < that.numer * this.denom
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 30 日午後 3:02 UTC](https://forum.ficusonline.com/t/topic/385/26 "2020-10-30T15:02:09Z")
## Predef
> **[Predef](https://www.scala-lang.org/api/current/scala/Predef$.html)**
### Assertions
These methods support program verification and runtime correctness.
```java
final def assert(assertion: Boolean, message: => Any): Unit
Tests an expression, throwing an AssertionError if false.
def assert(assertion: Boolean): Unit
Tests an expression, throwing an AssertionError if false.
final def assume(assumption: Boolean, message: => Any): Unit
Tests an expression, throwing an AssertionError if false.
def assume(assumption: Boolean): Unit
Tests an expression, throwing an AssertionError if false.
final def require(requirement: Boolean, message: => Any): Unit
Tests an expression, throwing an IllegalArgumentException if false.
def require(requirement: Boolean): Unit
Tests an expression, throwing an IllegalArgumentException if false.
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 10 月 31 日午前 9:41 UTC](https://forum.ficusonline.com/t/topic/385/27 "2020-10-31T09:41:40Z")
## def, val, var
>
**def** - defines an immutable label for the right side content which is lazily evaluated - evaluate by name.
**val** - defines an immutable label for the right side content which is eagerly/immediately evaluated - evaluated by value.
**var** - defines a mutable variable, initially set to the evaluated right side content.
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 11 月 9 日午前 6:32 UTC](https://forum.ficusonline.com/t/topic/385/28 "2020-11-09T06:32:19Z")
### LazyLists " #:: "
> **[Concrete Immutable Collection Classes](https://docs.scala-lang.org/overviews/collections-2.13/concrete-immutable-collection-classes.html)**
以下のようなフィボナッチ数列の演算で、 **#::** とすることで結果を呼び出さない限り演算しないようにする。
```auto
scala> def fibFrom(a: Int, b: Int): LazyList[Int] = a #:: fibFrom(b, a + b)
def fibFrom(a: Int, b: Int): LazyList[Int]
```
パラメータ入力しても演算結果を返さない。
```auto
scala> val fibs = fibFrom(1, 1).take(7)
val fibs: scala.collection.immutable.LazyList[Int] = LazyList()
```
**toList** メソッドによる呼び出し
```auto
scala> fibs.toList
val res0: List[Int] = List(1, 1, 2, 3, 5, 8, 13)
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 11 月 12 日午前 2:39 UTC](https://forum.ficusonline.com/t/topic/385/29 "2020-11-12T02:39:49Z")
### POLYMORPHIC METHODS
> **[def listOfDuplicates\[A\](x: A, length: Int): List\[A\] = { if (length \< 1) Nil... -...](https://docs.scala-lang.org/tour/polymorphic-methods.html#inner-main)**
>
> Methods in Scala can be parameterized by type as well as by value. The syntax is similar to that of generic classes. Type parameters are enclosed in square brackets, while value parameters are enclosed in parentheses.
型をパラメータとする場合 **[]** 、変数は **( )** を用います。型をパラメータと定義することでメソッドの自由度が大幅に増加します。 **println** 等による具体的な値を入力して呼び出しする際には **[]** は省略できます（Scalaコンパイラーによる自動認識）。
```auto
def listOfDuplicates[A](x: A, length: Int): List[A] = {
if (length < 1)
Nil
else
x :: listOfDuplicates(x, length - 1)
}
println(listOfDuplicates[Int](3, 4)) // List(3, 3, 3, 3)
println(listOfDuplicates("La", 8)) // List(La, La, La, La, La, La, La, La)
```
> **[Scala School - Type & polymorphism basics](http://twitter.github.io/scala_school/type-basics.html)**
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 11 月 20 日午前 2:15 UTC](https://forum.ficusonline.com/t/topic/385/30 "2020-11-20T02:15:23Z")
### コンパイラオプション
> **[Scala Compiler Options](https://docs.scala-lang.org/overviews/compiler-options/index.html#Standard_Settings)**
**scala.sbt**
```auto
scalaVersion := "2.13.3"
scalacOptions ++= Seq(
"-encoding", "utf8", // Option and arguments on same line
"-Xfatal-warnings", // New lines for each options
"-deprecation",
"-unchecked",
"-language:implicitConversions",
"-language:higherKinds",
"-language:existentials",
"-language:postfixOps"
)
```
---
### Author:  [@tk-fuse](https://forum.ficusonline.com/u/tk-fuse)
#### Post date: [2020 年 11 月 30 日午前 5:55 UTC](https://forum.ficusonline.com/t/topic/385/31 "2020-11-30T05:55:48Z")
## ScalaTest
**ScalaTestホーム**
> **[ScalaTest](https://www.scalatest.org/)**
**バージョン別ドキュメント**
> **[ScalaTest](https://www.scalatest.org/scaladoc)**
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