Java Articles - Page 189 of 445

Enumeration (enum) in Java is a datatype which stores a set of constant values. You can use enumerations to store fixed values such as days in a week, months in a year etc.You can define an enumeration using the keyword enum followed by the name of the enumeration as −enum Days {    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }Methods and variables in an enumerationEnumerations are similar to classes and, you can have variables, methods (Only concrete methods) and constructors within them.For suppose we have elements in an enumeration with values as −enum Scoters {    ACTIVA125(80000), ACTIVA5G(70000), ACCESS125(75000), ... Read More

Overloading is one of the mechanisms to achieve polymorphism where, a class contains two methods with same name and different parameters. It allows one method to perform different tasks based on the parameters passed to it. Whenever you call this method, the method body will be bound with the method call based on the parameters we pass to it. Constructor Overloading in Java Constructors are special methods that are called when an object is created. Constructor overloading in Java allows a class to have multiple constructors with different parameters. This is useful when you want to create objects in ... Read More

An interface in Java is similar to class but, it contains only abstract methods and fields which are final and static.A static method is declared using the static keyword and it will be loaded into the memory along with the class. You can access static methods using class name without instantiation.Static methods in an interface since java8Since Java8 you can have static methods in an interface (with body). You need to call them using the name of the interface, just like static methods of a class.ExampleIn the following example, we are defining a static method in an interface and accessing ... Read More

Static variables − Static variables are also known as class variables. You can declare a variable static using the keyword. Once you declare a variable static there would only be one copy of it in the class, regardless of how many objects are created from it.public static int num = 39;Instance variables − These variables belong to the instances (objects) of a class. These are declared within a class but outside methods. These are initialized when the class is instantiated. They can be accessed from any method, constructor or blocks of that particular class.You must access instance variables using an ... Read More

The only possible solution is to get the stack trace of the current thread. Get the class name using an element in the stack trace. Pass it to the forName() method of the class named Class.This returns a Class object and you can get an instance of this class using the newInstance() method.Examplepublic class MyClass {    String name = "Krishna";    private int age = 25;    public MyClass() {       System.out.println("Object of the class MyClass");       System.out.println("name: "+this.name);       System.out.println("age: "+this.age);    }    public static void demoMethod() throws Exception {   ... Read More

A class in Java will have three kinds of variables namely, static (class), instance and, local.Local variables − These variables belong to and declared/defined within the methods/blocks/constructors. The scope of these variables lies within the method (or, block or, constructor) and will be destroyed after he execution of it.Instance variables − These variables belong to the instances (objects) of a class. These are declared within a class but outside methods. These are initialized when the class is instantiated. They can be accessed from any method, constructor or blocks of that particular class.You must access instance variables using an object. i.e. ... Read More

A method which does not have body is known as abstract method. It contains only method signature with a semi colon and, an abstract keyword before it.public abstract myMethod();To use an abstract method, you need to inherit it by extending its class and provide implementation to it.Abstract classA class which contains 0 or more abstract methods is known as abstract class. If it contains at least one abstract method, it must be declared abstract.Hence, if you want to prevent instantiation of a class directly, you can declare it abstract.Accessing non-static methods of an abstract classSince you cannot instantiate an abstract ... Read More

When we have two classes where, one extends another and if, these two classes have same method including parameters and return type (say, sample) the method in the sub class overrides the method in the super class.i.e. Since it is inheritance. If we instantiate the subclass a copy of superclass’s members is created in the subclass object and, thus both methods are available to the object of the subclass.But if you call the method (sample), the sample method of the subclass will be executed overriding the super class’s method.Exampleclass Super{    public static void sample(){       System.out.println("Method of ... Read More

A static member (method/variable) belongs to the class and it will be loaded into the memory along with the class. You can invoke it without creating an object. (using the class name as reference). There is only one copy of the static field available throughout the class i.e. the value of the static field will be same in all objects. You can define a static field using the static keyword.Examplepublic class Sample{    static int num = 50;    public static void demo(){       System.out.println("Value of num in the demo method "+ Sample.num);    } } public class ... Read More

Factory pattern is a design pattern (creational pattern) which is used to create multiple objects based on the data we provide. In it we create an object abstracting the process of creation.ExampleBelow given is the example implementation of the factory pattern. Here, we have an interface with name Employee and 3 classes: Student, Lecturer, NonTeachingStaff, implementing it. We have created a factory class (EmployeeFactory) with a method named getEmployee(). This method accepts a String value and returns an object of one of the classes, based on the given String value.import java.util.Scanner; interface Person{    void dsplay(); } class Student implements ... Read More