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In the Java programming language, the final keyword is used in several contexts to define an entity that can only be assigned once.. Once a final variable has been assigned, it always contains the same value.
public class Fruit {} // parent class public class Apple extends Fruit {} // child class public static void main (String [] args) {// The following is an implicit upcast: Fruit parent = new Apple (); // The following is a downcast. Here, it works since the variable `parent` is // holding an instance of Apple: Apple child = (Apple) parent;}
Static import is a feature introduced in the Java programming language that allows members (fields and methods) which have been scoped within their container class as public static, to be used in Java code without specifying the class in which the field has been defined.
public The public keyword is used in the declaration of a class, method, or field; public classes, methods, and fields can be accessed by the members of any class. [17] return Used to finish the execution of a method. It can be followed by a value required by the method definition that is returned to the caller. short
In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
import static java.lang.System.out; //'out' is a static field in java.lang.System public class HelloWorld {public static void main (String [] args) {/* The following line is equivalent to System.out.println("Hi World!"); and would have been incorrect without the import declaration. */ out. println ("Hello World!");}}
The static modifier states that a member belongs to the class and not to a specific object. Classes marked static are only allowed to contain static members. Static members are sometimes referred to as class members since they apply to the class as a whole and not to its instances.
Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are thread safe and implement a singleton pattern. When used in a generic programming class, static constructors are called at every new generic instantiation one per type. [8]: 38 [4]: 111 Static variables are instantiated as well.