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public class Base {public void m1 {...} public final void m2 {...} public static void m3 {...} public static final void m4 () ... Java's primitive types are immutable ...
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.
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!");}}
In all versions of Java, the idiom enables a safe, highly concurrent lazy initialization of static fields with good performance. [ 1 ] [ 2 ] public class Something { private Something () {} private static class LazyHolder { static final Something INSTANCE = new Something (); } public static Something getInstance () { return LazyHolder .
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:
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;}
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).
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