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

Whenever you return values from a static method they are either static nor instance by default, they are just values.The user invoking the method can use them as he wants. i.e. you can retrieve the values and declare them static.But, since you cannot declare variables of a method static if you need to declare the vales returned by a method static you need to invoke it in the class outside the methods.ExampleAssume we have a class with name Demo as −class Demo{    int data = 20;    public Demo(int data){       this.data = data;    }   ... Read More

The static methods belong to the class and they will be loaded into the memory along with the class. You can invoke them without creating an object. (using the class name as reference).Examplepublic class Sample{    static int num = 50;    public static void demo(){       System.out.println("Contents of the static method");    }    public static void main(String args[]){       Sample.demo();    } }OutputContents of the static methodThe "this" keyword is used as a reference to an instance. Since the static methods doesn’t have (belong to) any instance you cannot use the "this" reference within ... Read More

A static filed/variable belongs to the class and it will be loaded into the memory along with the class. You can invoke them 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 void demo(){       System.out.println("Value of num in the demo method "+ Sample.num);    }    public static void main(String ... Read More

A static method or, block belongs to the class and these will be loaded into the memory along with the class. You can invoke static methods without creating an object. (using the class name as reference).Where the "super" keyword in Java is used as a reference to the object of the superclass. This implies that to use "super" the method should be invoked by an object, which static methods are not.Therefore, you cannot use the "super" keyword from a static method.ExampleIn the following Java program, the class "SubClass" contains a private variable name with setter and getter methods and an ... Read More

A static filed/variable belongs to the class and it will be loaded into the memory along with the class. You can invoke them 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 void demo(){       System.out.println("Value of num in the demo method "+ Sample.num);    }    public static void main(String ... Read More