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Static classes in C#, which can't be instantiated. Inner classes in Java implicitly carry a this reference to the outer class object and must exist in the context of an outer class instance. By declaring an inner class to be static, it does not carry such a reference and can be used independently to an outer class instance. The static keyword ...
Inner class – The following categories are called inner classes. Each instance of these classes has a reference to an enclosing instance (i.e. an instance of the enclosing class), except for local and anonymous classes declared in static context. Hence, they can implicitly refer to instance variables and methods of the enclosing class.
abstract - Specifies that a class only serves as a base class and cannot be instantiated. static - Used only for member classes, specifies that the member class does not belong to a specific instance of the containing class. final - Classes marked as final cannot be extended from and cannot have any subclasses.
An interface in the Java programming language is an abstract type that is used to declare a behavior that classes must implement. They are similar to protocols.Interfaces are declared using the interface keyword, and may only contain method signature and constant declarations (variable declarations that are declared to be both static and final).
Also, derived classes can override inherited methods if the language allows. Not all languages support multiple inheritance. For example, Java allows a class to implement multiple interfaces, but only inherit from one class. [22] If multiple inheritance is allowed, the hierarchy is a directed acyclic graph (or DAG for short), otherwise it is a ...
A singleton implementation may use lazy initialization in which the instance is created when the static method is first invoked. In multithreaded programs, this can cause race conditions that result in the creation of multiple instances. The following Java 5+ example [6] is a thread-safe implementation, using lazy initialization with double ...
According to Java Language Specification: [5] A type variable is an unqualified identifier. Type variables are introduced by generic class declarations, generic interface declarations, generic method declarations, and by generic constructor declarations. A class is generic if it declares one or more type variables. [6]
public final class Constants {private Constants {// restrict instantiation} public static final double PI = 3.14159; public static final double PLANCK_CONSTANT = 6.62606896e-34;} Since Java 5 , one can use static import [ 4 ] to be able to use the constants without the Constants qualifier: