What is Singleton?
Restricts a class to instantiate its multiple objects and allows only one instance that has a control throughout the execution
Required properties: (1) should have only one instance and (2) should be globally accessible
Initialization
- Early Initialization – initialize when the class gets loaded
- Advantage: Simplicity
- Disadvantage: it’s always initialized whether it is being used or not.
class SingletonClass {
private static SingletonClass object = new SingletonClass();
private SingletonClass() {}
public static SingletonClass getInstance() {
return object;
}
}
- Lazy Initialization – initialize only when it is required (general way to create a singleton class)
class SingletonClass {
private static SingletonClass object;
private SingletonClass() {}
public static SingletonClass getInstance() {
if(object == null) {
object = new SingletonClass();
}
return object;
}
}
Examples of Singleton class
- Java.lang.Runtime – every app has a singleton instance of class Runtime to interface
- Logger – suitable for single log file generation that can prevent concurrent access
- Cache – client apps are able to use in-memory object with global point of reference.
References
- https://www.geeksforgeeks.org/singleton-design-pattern-introduction/
- https://stackoverflow.com/questions/19068468/what-is-meant-by-early-initialization-of-a-singleton-class-in-java
Xamarin, ReactNative and Titanium are similar but using different languages. Flutter is the latest framework from Google, and its key feature is providing full UI stack implementation without using native UI components. This means UIs will be exactly the same on different platforms. Other three frameworks link with original framework, and that means UIs will be slightly different on different platforms. Also, Flutter is fast and smooth because of no need for linking with original frameworks.