プログラミング言語の比較 > クラスとインスタンス

値を変更できる（mutable）人物クラス

名前と年齢を保持するクラスを定義して、インスタンス化し、名前と年齢をセットして文字列に変換する。

Java

class Person {
private String name;
private int age;
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public int getAge() { return age; }
public void setAge(int age) { this.age = age; }
@Override
public String toString() {
return String.format("%s (%d years old)", name, age);
}
}

Person p = new Person();
p.setName("Taro");
p.setAge(20);
String s = p.toString();

Groovy

class Person {
String name
int age
@Override String toString() { "${name} (${age} years old)" }
}

def p = new Person(name: 'Taro', age: 20)
def s = p.toString()

Kotlin

class Person {
var name: String? = null
var age = 0
override fun toString() = "$name ($age years old)"
}

val p = Person()
p.name = "Taro"
p.age = 20
val s = p.toString()

Scala

class Person {
var name: String = _
var age: Int = _
override def toString = "%s (%d years old)".format(name, age)
}

class Person(var name: String, var age: Int) {
def this() = this(null, 0)
override def toString = "%s (%d years old)".format(name, age)
}

val p = new Person
p.name = "Taro"
p.age = 20
val s = p.toString

F#

type Person() =
member val Name = "" with get, set
member val Age = 0 with get, set
override this.ToString() = sprintf "%s (%d years old)" this.Name this.Age

let p = new Person()
p.Name <- "Taro"
p.Age <- 20
let s = p.ToString()

C#

class Person {
public string Name { get; set; }
public int Age { get; set; }
public override string ToString() {
return $"{Name} ({Age} years old)";
}
}

var p = new Person { Name = "Taro", Age = 20 };
string s = p.ToString();

C++

#include <strstream>
class person {
public:
string name;
int age;
operator string();
};
// person クラスから文字列への変換関数
person::operator string() {
strstream ss;
ss << name << " (" << age << " years old)";
return ss.str();
}

person p;
p.name = "Taro";
p.age = 20;
string s = p;

person p;
p.name = "Taro";
p.age = 20;
string s = static_cast<string>(p);

Go

type Person struct {
Name string
Age int
}
func (this *Person) String() string {
return fmt.Sprintf("%s (%d years old)", this.Name, this.Age)
}

p := Person{"Taro", 20}
s := p.String()

p := Person{Name: "Taro", Age: 20}
s := p.String()

var p Person
p.Name = "Taro"
p.Age = 20
s := p.String()

Rust

pub struct Person<'a> {
pub name: &'a str,
pub age: i32,
}
impl<'a> fmt::Display for Person<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{} ({} years old)", self.name, self.age)
}
}

let mut p = Person {
name: "",
age: 0,
};
p.name = "Taro";
p.age = 20;
let s = format!("{p}");

Dart

class Person {
String? _name;
String? get name => _name;
set name(String? name) => _name = name;
int? _age;
int? get age => _age;
set age(int? age) => _age = age;
toString() => '$name ($age years old)';
}

var p = Person();
p.name = 'Taro';
p.age = 20;
var s = p.toString();

TypeScript

class Person {
name: string;
age: number;
toString() {
return `${this.name} (${this.age} years old)`
}
}

let p = new Person();
p.name = 'Taro';
p.age = 20;
let s = p.toString();

JavaScript

class Person {
name;
age;
toString() {
return `${this.name} (${this.age} years old)`;
}
}

let p = new Person();
p.name = 'Taro';
p.age = 20;
let s = String(p);

CoffeeScript

class Person
constructor: (@name, @age) ->
toString: -> "#{@name} (#{@age} years old)"

p = new Person 'Taro', 20
s = String p

Ruby

class Person
attr_accessor :name, :age
def to_s
"#{name} (#{age} years old)"
end
end

p = Person.new
p.name = 'Taro'
p.age = 20
s = p.to_s

Python

class Person:
name = None # 省略可
age = None # 省略可
def __str__(self):
return '%s (%d years old)' % (self.name, self.age)

p = Person()
p.name = 'Taro'
p.age = 20
s = str(p)

PHP

class Person {
public $name;
public $age;
public function __toString() {
return "{$this->name} ({$this->age} years old)";
}
}

$p = new Person();
$p->name = 'Taro';
$p->age = 20;
$s = (string)$p;

PHP

PHP 7.4以降

class Person {
public string $name;
public int $age;
public function __toString() {
return "{$this->name} ({$this->age} years old)";
}
}

Perl

package Person;
use overload q/""/ => sub { # 文字列への変換関数
my $self = shift;
"$self->{name} ($self->{age} years old)";
};
sub new {
my $class = shift;
bless {}, $class;
}

# use Person;
my $p = Person->new;
$p->{name} = 'Taro';
$p->{age} = 20;
my $s = "$p";

CPAN の Class::Accessor::Lvalue を使った場合

package Person;
use base qw/Class::Accessor::Lvalue::Fast/;
use overload q/""/ => sub { # 文字列への変換関数
my $self = shift;
"$self->{name} ($self->{age} years old)";
};
__PACKAGE__->mk_accessors(qw/name age/); # ゲッター・セッターを作る

# use Person;
my $p = Person->new;
$p->name = 'Taro';
$p->age = 20;
my $s = "$p";

CPAN の Class::MethodMaker を使った場合

package Person;
use overload q/""/ => sub { # 文字列への変換関数
my $self = shift;
"$self->{name} ($self->{age} years old)";
};
use Class::MethodMaker [
new => [qw/new/], # コンストラクタを作る
scalar => [qw/name age/], # ゲッター・セッターを作る
];

# use Person;
my $p = Person->new;
$p->name('Taro');
$p->age(20);
my $s = "$p";

値を変更できない（immutable）人物クラス

インスタンス化の際に引数で名前と年齢を指定し、その後それらの値を読み出す。

Java

class Person {
private final String name;
private final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() { return name; }
public int getAge() { return age; }
}

Person p = new Person("Taro", 20);
String name = p.getName();
int age = p.getAge();

Java 16以降

record Person(String name, int age) {}

Person p = new Person("Taro", 20);
String name = p.name();
int age = p.age();

Groovy

class Person {
private final name
private final age
Person(name, age) {
this.name = name
this.age = age
}
String getName() { name }
int getAge() { age }
}

def p = new Person("Taro", 20)
def name = p.name
def age = p.age

Kotlin

class Person(val name: String, val age: Int)

val p = Person("Taro", 20)
val name = p.name
val age = p.age

Scala

class Person(val name: String, val age: Int)

val p = new Person("Taro", 20)
val name = p.name
val age = p.age

case class Person(name: String, age: Int)

val p = Person("Taro", 20)
val name = p.name
val age = p.age

Haskell

data Person = Person {name :: String, age :: Integer}
instance Show Person where
show = \ p -> (name p) ++ " (" ++ (show $ age p) ++ " years old)"

let p = Person "Taro" 20
let name' = name p
let age' = age p

F#

type Person(name : string, age: int) =
member val Name = name with get
member val Age = age with get

let p = new Person("Taro", 20)
let name = p.Name
let age = p.Age

C#

C# 6.0以降

class Person {
public string Name { get; }
public int Age { get; }
public Person(string name, int age) {
Name = name;
Age = age;
}
}

var p = new Person("Taro", 20);
string name = p.Name;
int age = p.Age;

C# 7.0以降

class Person {
public string Name { get; }
public int Age { get; }
public Person(string name, int age) => (Name, Age) = (name, age);
}

C# 9.0以降

record Person(string Name, int Age);

C++

class person {
public:
person(const string name, const int age) : _name(name), _age(age) {}
string name() const { return _name; }
int age() const { return _age; }
private:
const string _name;
const int _age;
};

person p("Taro", 20);
string name = p.name();
int age = p.age();

person* p = new person("Taro", 20);
string name = p->name();
int age = p->age();
delete p;

Go

type Person struct {
name string // 小文字で始まるフィールドは private になるので外から見えない
age int
}
func (this *Person) Name() string { // public なゲッター
return this.name
}
func (this *Person) Age() int {
return this.age
}

p := Person{"Taro", 20}
name := p.Name()
age := p.Age()

p := Person{name: "Taro", age: 20}
name := p.Name()
age := p.Age()

Rust

pub struct Person<'a> {
name: &'a str,
age: i32,
}
impl<'a> Person<'a> {
fn name(&self) -> &'a str {
self.name
}
fn age(&self) -> i32 {
self.age
}
}

let p = Person {
name: "Taro",
age: 20,
};
let name = p.name();
let age = p.age();

Dart

class Person {
final String _name;
get name => _name;
final int _age;
get age => _age;
Person(this._name, this._age);
}

var p = new Person('Taro', 20);
var name = p.name;
var age = p.age;

TypeScript

class Person {
constructor(readonly name: string, readonly age: number) {}
}

let p = new Person('Taro', 20);
let name = p.name;
let age = p.age;

JavaScript

class Person {
#name;
#age;
constructor(name, age) {
this.#name = name;
this.#age = age;
}
get name() {
return this.#name;
}
get age() {
return this.#age;
}
}

let p = new Person('Taro', 20);
let name = p.name;
let age = p.age;

CoffeeScript

class Person
constructor: (name, age) ->
Object.defineProperty @, 'name', value: name
Object.defineProperty @, 'age', value: age

p = new Person 'Taro', 20
name = p.name
age = p.age

Ruby

class Person
attr_reader :name, :age
def initialize name, age
@name = name
@age = age
end
end

p = Person.new 'Taro', 20
name = p.name
age = p.age

Python

class Person:
def __init__(self, name, age):
self.__name = name
self.__age = age
def name(self): return self.__name
def age(self): return self.__age

p = Person('Taro', 20)
name = p.name()
age = p.age()

Python 3.7以降

# import dataclasses
@dataclasses.dataclass(frozen=True)
class Person:
name: str
age: int

p = Person('Taro', 20)
name = p.name
age = p.age

PHP

class Person {
private $_name;
private $_age;
public function __construct($name, $age) {
$this->_name = $name;
$this->_age = $age;
}
public function name() {
return $this->_name;
}
public function age() {
return $this->_age;
}
}

$p = new Person('Taro', 20);
$name = $p->name();
$age = $p->age();

Perl

package Person;
sub new {
my $class = shift;
my $self;
$self->{$_} = shift for qw/name age/;
bless $self, $class;
}
sub name {
shift->{name};
}
sub age {
shift->{age};
}

# use Person;
my $p = Person->new('Taro', 20);
my $name = $p->name;
my $age = $p->age;

CPAN の Class::Accessor::Lvalue を使った場合

package Person;
use base qw/Class::Accessor::Lvalue::Fast/;
our @keys = qw/name age/;
__PACKAGE__->mk_ro_accessors(@keys); # ゲッターを作る
sub new {
my $class = shift;
my $self = $class->SUPER::new; # コンストラクタをオーバーライドする
$self->{$_} = shift for @keys;
$self;
}

# use Person;
my $p = Person->new('Taro', 20);
my $name = $p->name;
my $age = $p->age;

クラス名の文字列を元にインスタンスを生成する

Java

String className = "Person";
Object p = Class.forName(className).getConstructors()[0].newInstance("Taro", 20);

Groovy

def className = 'Person'
def p = Class.forName(className).getConstructors()[0].newInstance('Taro', 20)

Kotlin

val className = "Person"
val p = Class.forName(className).getConstructors()[0].newInstance("Taro", 20)

Scala

val className = "Person"
val p = Class.forName(className).getConstructors()(0).newInstance("Taro", 20.asInstanceOf[AnyRef])

val className = "Person"
val args = List("Taro", 20).map(_.asInstanceOf[AnyRef]).toArray
val p = Class.forName(className).getConstructors()(0).newInstance(args: _*)

F#

let className = "Person"
let p = System.Type.GetType(className).GetConstructors().[0].Invoke [|"Taro"; 20|]

C#

string className = "Person";
object p = Type.GetType(className).GetConstructors()[0].Invoke(new object[] { "Taro", 20 });

TypeScript

let className = 'Person';
let p = new (eval(className))('Taro', 20);

JavaScript

let className = 'Person';
let p = new (eval(className))('Taro', 20);

CoffeeScript

className = 'Person'
p = new (eval className) 'Taro', 20

Ruby

class_name = 'Person'
p = eval(class_name).new('Taro', 20)

Python

class_name = 'Person'
p = eval(class_name)('Taro', 20)

PHP

$className = 'Person';
$p = new $className('Taro', 20);

Perl

my $class_name = 'Person';
my $p = $class_name->new('Taro', 20);

文字列クラスの3世代親のクラスを取得する（なければ null）

Java

Class<?> clazz = "".getClass();
for (int i = 0; i < 3; i++) {
clazz = clazz.getSuperclass();
if (clazz == null) break;
}

Groovy

def clazz = ''.class
3.times { clazz = clazz?.superclass }

Kotlin

var clazz: Class<*>? = "".javaClass
(1..3).forEach { clazz = clazz?.getSuperclass() }

Scala

var clazz = "".getClass
(1 to 3).foreach(_ => if (clazz != null) clazz = clazz.getSuperclass)

F#

let f (typ : Type) _ =
match typ with
| null -> null
| typ -> typ.BaseType
let typ = Seq.fold f ("".GetType()) [1..3]

let f = function
| null -> null
| (typ : Type) -> typ.BaseType
let typ = Seq.fold (fun typ _ -> f typ) ("".GetType()) [1..3]

let mutable typ = "".GetType()
for i = 1 to 3 do
match typ with
| null -> ()
| t -> typ <- t.BaseType

C#

Type type = "".GetType();
for (int i = 0; i < 3; i++) {
type = type.BaseType;
if (type == null) break;
}

C# 6.0以降

Type type = "".GetType();
for (int i = 0; i < 3; i++) {
type = type?.BaseType;
}

Ruby

clazz = ''.class
3.times { clazz = clazz.superclass unless clazz.nil? }

Python

文字列クラスが多重継承をしていない前提でなら

# import inspect
t = type('')
try:
t = inspect.getmro(t)[3]
except IndexError:
None

オブジェクトの内容（メンバー変数の名前と値）を文字列で表す

Java

Commons Lang を使った場合

// import org.apache.commons.lang3.builder.ToStringBuilder;
Object = ... // 任意のオブジェクト
String s = ToStringBuilder.reflectionToString(obj);

Groovy

def obj = ... // 任意のオブジェクト
def s = obj.dump()

Scala

case class の場合。名前は含まれないが…

val obj = ... // case class のオブジェクト
val s = obj.toString

Go

obj := ... // 任意の値
s := fmt.Sprint(obj)

TypeScript

Node.js の場合

// import * as util from 'util';
let obj = ...
let s = util.inspect(obj);

JavaScript

Node.js の場合

// const util = require('util');
let obj = ...
let s = util.inspect(obj);

CoffeeScript

Node.js の場合

# util = require 'util'
obj = ...
s = util.inspect obj

Ruby

obj = ... # 任意のオブジェクト
s = obj.inspect

Python

obj = ... # 任意のオブジェクト
s = repr(obj.__dict__)

もう少し見栄えを良くしたければ

# import re
obj = ... # 任意のオブジェクト
r = re.compile('^_.+__')
s = ', '.join(r.sub('__', name) + ': ' + repr(value) for name, value in obj.__dict__.items())

PHP

$obj = ... // 任意のオブジェクト
$s = var_export($obj, true);

もう少し見栄えを良くしたければ

$obj = ... // 任意のオブジェクト
$vars = get_object_vars($obj);
foreach ($vars as $name => &$value) {
$value = $name . ': ' . var_export($value, true);
}
$s = implode(', ', $vars);

Perl

# use Data::Dumper;
my $obj = ...; # 任意のオブジェクト
my $s = Dumper($obj);

既存のクラスにメソッドを追加する

Groovy

メタクラスを使う方法

String.metaClass.up = { delegate.toUpperCase() }

カテゴリーを使う方法

class StringCategory {
static up(String s) {
s.toUpperCase()
}
}

use (StringCategory.class) {
println 'abc'.up() // StringCategory.up('abc') と解釈される
}

Kotlin

fun String.up() = this.toUpperCase()

println("abc".up())

Scala

Scala 3.0以降

extension (s: String)
def up = s.toUpperCase

println("abc".up) // new StringEx("abc").up() と解釈される

C#

public static class StringEx {
public static string Up(this string s) {
return s.ToUpper();
}
}

TypeScript

declare global {
interface String {
up(): string;
}
}
String.prototype.up = function() {
return this.toUpperCase();
};

JavaScript

String.prototype.up = function() { return this.toUpperCase(); };

CoffeeScript

String::up = -> @toUpperCase()

Ruby

class String
def up
upcase
end
end

module StringEx
refine String do
def up
upcase
end
end
end

using StringEx
puts 'abc'.up

目次
値を変更できる（mutable）人物クラス	Java	Groovy	Kotlin	Scala	Erlang	Haskell	PowerShell	F#	C#	C++	Go	Rust	Dart	TypeScript	JavaScript	CoffeeScript	Ruby	Python	PHP	Perl
値を変更できない（immutable）人物クラス	Java	Groovy	Kotlin	Scala	Erlang	Haskell	PowerShell	F#	C#	C++	Go	Rust	Dart	TypeScript	JavaScript	CoffeeScript	Ruby	Python	PHP	Perl
クラス名の文字列を元にインスタンスを生成する	Java	Groovy	Kotlin	Scala	Erlang	Haskell	PowerShell	F#	C#	C++	Go	Rust	Dart	TypeScript	JavaScript	CoffeeScript	Ruby	Python	PHP	Perl
文字列クラスの3世代親のクラスを取得する（なければ null）	Java	Groovy	Kotlin	Scala	Erlang	Haskell	PowerShell	F#	C#	C++	Go	Rust	Dart	TypeScript	JavaScript	CoffeeScript	Ruby	Python	PHP	Perl
オブジェクトの内容（メンバー変数の名前と値）を文字列で表す	Java	Groovy	Kotlin	Scala	Erlang	Haskell	PowerShell	F#	C#	C++	Go	Rust	Dart	TypeScript	JavaScript	CoffeeScript	Ruby	Python	PHP	Perl
既存のクラスにメソッドを追加する	Java	Groovy	Kotlin	Scala	Erlang	Haskell	PowerShell	F#	C#	C++	Go	Rust	Dart	TypeScript	JavaScript	CoffeeScript	Ruby	Python	PHP	Perl