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👉 Singleton パターン - Wikipedia 
■ "java singleton"
In Java, a singleton is a design pattern that ensures that a class has only one instance and provides a global point of access to it. This is useful when you need to have only one instance of a class for the entire application, such as for managing a shared resource.
To implement a singleton in Java, you would typically create a static member in the class that holds the sole instance of the class, and provide a static method that returns the instance. This method is typically called getInstance(). Here is an example:
public class Singleton {
private static Singleton instance;
private Singleton() {
// Private constructor to prevent instantiation
}
public static Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
To use the singleton, you would call the getInstance() method, like this:
Singleton instance = Singleton.getInstance();
It is important to note that a singleton in Java is not thread-safe by default. If multiple threads can access the getInstance() method simultaneously, it is possible for two or more instances of the class to be created. To make the singleton thread-safe, you can use synchronization in the getInstance() method, like this:
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
This ensures that only one thread can execute the getInstance() method at a time, which prevents multiple instances of the class from being created.
■ "javaでシングルトン"
Javaでシングルトンとは、あるクラスが1つのインスタンスだけを持ち、そのインスタンスに対するグローバルなアクセスポイントを提供するデザインパターンです。これは、アプリ全体で1つのクラスのインスタンスだけが必要な場合に役立ちます。例えば、共有リソースの管理などです。
Javaでシングルトンを実装するには、通常はクラス内にクラスの唯一のインスタンスを保持するための静的メンバーを作成し、そのインスタンスを返す静的メソッドを提供します。このメソッドは通常、getInstance()と呼ばれます。以下に例を示します。
public class Singleton {
private static Singleton instance;
private Singleton() {
// Private constructor to prevent instantiation
}
public static Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
シングルトンを使用するには、getInstance()メソッドを呼び出します。以下はその例です。
Singleton instance = Singleton.getInstance();
Javaでのシングルトンはデフォルトでスレッドセーフではありません。複数のスレッドが同時にgetInstance()メソッドにアクセスできる場合、クラスの2つ以上のインスタンスが作成される可能性があります。シングルトンをスレッドセーフにするには、getInstance()メソッド内で同期を使用します。以下に例を示します。
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
これにより、1つのスレッドだけがgetInstance()メソッドを実行できるようになり、クラスの複数のインスタンスが作成されることを防ぎます。
■ "java で singleton"
Javaでのシングルトンとは、あるクラスが1つのインスタンスだけを持ち、そのインスタンスに対するグローバルなアクセスポイントを提供するデザインパターンです。これは、アプリ全体で1つのクラスのインスタンスだけが必要な場合に役立ちます。例えば、共有リソースの管理などです。
Javaでシングルトンを実装するには、通常はクラス内にクラスの唯一のインスタンスを保持するための静的メンバーを作成し、そのインスタンスを返す静的メソッドを提供します。このメソッドは通常、getInstance()と呼ばれます。以下に例を示します。
public class Singleton {
private static Singleton instance;
private Singleton() {
// Private constructor to prevent instantiation
}
public static Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
シングルトンを使用するには、getInstance()メソッドを呼び出します。以下はその例です。
Singleton instance = Singleton.getInstance();
Javaでのシングルトンはデフォルトでスレッドセーフではありません。複数のスレッドが同時にgetInstance()メソッドにアクセスできる場合、クラスの2つ以上のインスタンスが作成される可能性があります。シングルトンをスレッドセーフにするには、getInstance()メソッド内で同期を使用します。以下に例を示します。
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
これにより、1つのスレッドだけがgetInstance()メソッド
■ "kotlin singleton"
In Kotlin, a singleton is a design pattern that ensures that a class has only one instance and provides a global point of access to it. This is useful when you need to have only one instance of a class for the entire application, such as for managing a shared resource.
To implement a singleton in Kotlin, you can use the object keyword. This keyword is used to create a single instance of a class. Here is an example:
object Singleton {
fun doSomething() {
// Code to perform some operation
}
}
To use the singleton, you can simply call its methods like any other object, without the need to call a getInstance() method:
Singleton.doSomething()
One advantage of using the object keyword to implement a singleton in Kotlin is that it is thread-safe. Because the object keyword creates a single instance of the class, and because this instance is created when the class is loaded, multiple threads cannot access the getInstance() method simultaneously, and so it is not possible for multiple instances of the class to be created. This means you do not need to use synchronization to make the singleton thread-safe.
■ kotlin で singleton
Kotlinでのシングルトンとは、あるクラスが1つのインスタンスだけを持ち、そのインスタンスに対するグローバルなアクセスポイントを提供するデザインパターンです。これは、アプリ全体で1つのクラスのインスタンスだけが必要な場合に役立ちます。例えば、共有リソースの管理などです。
Kotlinでシングルトンを実装するには、objectキーワードを使用します。このキーワードは、クラスの1つのインスタンスを作成するために使用されます。以下は例です。
object Singleton {
fun doSomething() {
// Code to perform some operation
}
}
シングルトンを使用するには、getInstance()メソッドを呼ぶ必要がないので、他のオブジェクトのように単にそのメソッドを呼び出します。以下はその例です。
Singleton.doSomething()
Kotlinでシングルトンを実装する際に、objectキーワードを使用する利点の1つは、それがスレッド
■ "dagger singleton"
Dagger is a dependency injection framework for the Java and Android platform. It is not itself a singleton, but rather a framework for creating and managing objects that are singletons or have other specific scope.
To create a singleton with Dagger, you would first define a class that provides the singleton instance. This class is called a "module" in Dagger terminology. Here is an example of a singleton module in Dagger:
@Module
public class SingletonModule {
private static Singleton instance;
@Provides
@Singleton
public Singleton provideSingleton() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
Next, you would define a "component" that uses the module to provide the singleton instance to other classes. Here is an example of a component that uses the above module:
@Component(modules = {SingletonModule.class})
public interface SingletonComponent {
Singleton getSingleton();
}
To use the singleton in your code, you would create an instance of the component and use it to get the singleton instance. Here is an example:
SingletonComponent component = DaggerSingletonComponent.create();
Singleton singleton = component.getSingleton();
In this example, the DaggerSingletonComponent class is generated by Dagger at compile time, based on the SingletonComponent interface. The create() method is a static factory method that creates an instance of the component.
By using Dagger to manage the singleton, you can avoid the need to use synchronization to make the singleton thread-safe, as Dagger takes care of this for you. Additionally, Dagger allows you to easily replace the singleton instance with a mock or test double in unit tests, which can make your tests more robust and easier to write.
■ "dagger2 singleton"
Dagger 2 is a dependency injection framework for the Java and Android platform. It is not itself a singleton, but rather a framework for creating and managing objects that are singletons or have other specific scope.
To create a singleton with Dagger 2, you would first define a class that provides the singleton instance. This class is called a "module" in Dagger terminology. Here is an example of a singleton module in Dagger 2:
@Module
public class SingletonModule {
private static Singleton instance;
@Provides
@Singleton
public Singleton provideSingleton() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
Next, you would define a "component" that uses the module to provide the singleton instance to other classes. Here is an example of a component that uses the above module:
@Component(modules = {SingletonModule.class})
public interface SingletonComponent {
Singleton getSingleton();
}
To use the singleton in your code, you would create an instance of the component and use it to get the singleton instance. Here is an example:
SingletonComponent component = DaggerSingletonComponent.builder().singletonModule(new SingletonModule()).build();
Singleton singleton = component.getSingleton();
In this example, the DaggerSingletonComponent class is generated by Dagger at compile time, based on the SingletonComponent interface. The builder() method is a static factory method that creates a builder for the component, which you can use to specify the module(s) to use.
By using Dagger 2 to manage the singleton, you can avoid the need to use synchronization to make the singleton thread-safe, as Dagger takes care of this for you. Additionally, Dagger 2 allows you to easily replace the singleton instance with a mock or test double in unit tests, which can make your tests more robust and easier to write.
■ "hilt singleton"
Hilt is a dependency injection framework for the Android platform, built on top of Dagger. It is not itself a singleton, but rather a framework for creating and managing objects that are singletons or have other specific scope.
To create a singleton with Hilt, you would first define a class that provides the singleton instance. This class is called a "module" in Hilt terminology. Here is an example of a singleton module in Hilt:
@Module
@InstallIn(ApplicationComponent.class)
public class SingletonModule {
private static Singleton instance;
@Provides
@Singleton
public Singleton provideSingleton() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
Next, you would annotate the class that wants to use the singleton with the @Inject annotation. Here is an example:
public class MyClass {
@Inject Singleton singleton;
// Code that uses the singleton goes here
}
To use the singleton in your code, you would create an instance of the class and use the singleton. Hilt will automatically inject the singleton into the class when it is created. Here is an example:
MyClass myClass = new MyClass();
Singleton singleton = myClass.singleton;
By using Hilt to manage the singleton, you can avoid the need to use synchronization to make the singleton thread-safe, as Hilt takes care of this for you. Additionally, Hilt allows you to easily replace the singleton instance with a mock or test double in unit tests, which can make your tests more robust and easier to write.
■ "Flutter singleton"
In Flutter, a singleton is a design pattern that ensures that a class has only one instance and provides a global point of access to it. This is useful when you need to have only one instance of a class for the entire application, such as for managing a shared resource.
To implement a singleton in Flutter, you can use the Singleton class from the singleton_pattern package. Here is an example of how to use it:
import 'package:singleton_pattern/singleton_pattern.dart';
class MySingleton extends Singleton<MySingleton> {
// Code for your singleton goes here
}
To use the singleton in your code, you would call the instance property of the class, like this:
MySingleton singleton = MySingleton.instance;
The Singleton class uses Dart's Isolates feature to ensure that the singleton is initialized only once and is thread-safe. This means you do not need to use synchronization to make the singleton thread-safe.
■ "Dart singleton"
In Dart, a singleton is a design pattern that ensures that a class has only one instance and provides a global point of access to it. This is useful when you need to have only one instance of a class for the entire application, such as for managing a shared resource.
To implement a singleton in Dart, you can use the Singleton class from the singleton_pattern package. Here is an example of how to use it:
import 'package:singleton_pattern/singleton_pattern.dart';
class MySingleton extends Singleton<MySingleton> {
// Code for your singleton goes here
}
To use the singleton in your code, you would call the instance property of the class, like this:
MySingleton singleton = MySingleton.instance;
The Singleton class uses Dart's Isolates feature to ensure that the singleton is initialized only once and is thread-safe. This means you do not need to use synchronization to make the singleton thread-safe.
Alternatively, you can implement a singleton in Dart using a static property and a private constructor. Here is an example:
class MySingleton {
static final MySingleton instance = MySingleton._();
MySingleton._(); // Private constructor
// Code for your singleton goes here
}
To use the singleton, you would call the instance property, like this:
MySingleton singleton = MySingleton.instance;
This implementation is not thread-safe, so you would need to use synchronization if multiple threads can access the instance property simultaneously. For example:
class MySingleton {
static final MySingleton _instance = MySingleton._();
static MySingleton get instance {
return _instance;
}
MySingleton._(); // Private constructor
// Code for your singleton goes here
}
In this example, the instance property is a getter that uses synchronization to ensure that only one thread can access it at a time. This prevents multiple instances of the class from being created.
■ "swift singleton"
In Swift, a singleton is a design pattern that ensures that a class has only one instance and provides a global point of access to it. This is useful when you need to have only one instance of a class for the entire application, such as for managing a shared resource.
To implement a singleton in Swift, you would typically create a static constant property in the class that holds the sole instance of the class, and provide a static method that returns the instance. This method is typically called shared or sharedInstance. Here is an example:
class Singleton {
static let shared = Singleton()
private init() {
// Private initializer to prevent instantiation
}
// Code for your singleton goes here
}
To use the singleton, you would call the shared property, like this:
let singleton = Singleton.shared
It is important to note that a singleton in Swift is not thread-safe by default. If multiple threads can access the shared property simultaneously, it is possible for two or more instances of the class to be created. To make the singleton thread-safe, you can use synchronization in the shared property, like this:
class Singleton {
static let shared: Singleton = {
let instance = Singleton()
return instance
}()
private init() {
// Private initializer to prevent instantiation
}
// Code for your singleton goes here
}
This ensures that only one thread can execute the shared property at a time, which prevents multiple instances of the class from being created.
■ まとめ
日本語で技術的なことを問う場合、英語、カタカナ、区切りなど複雑なので困ったりします。
コードについては、分かる人が見ればすぐに分かります。
どこかで見たような微妙なコードも含まれています。
｢とりあえずそれっぽい」ので分からない人には分かりません。
逆に、Google検索と同じように使う側の技量が問われることになりそうです。
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👉 Kotlin で書きたい「正しいシングルトン(Singleton)」 
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