Java Technology

 Introduction There are two types of modifiers in Java: access modifiers and non-access modifiers. The access modifiers in Java specifies the accessibility or scope of a field, method, constructor, or class. We can change the access level of fields, constructors, methods, and class by applying the access modifier on it. There are four types of Java access modifiers: 1. Private: The access level of a private modifier is only within the class. It cannot be accessed from outside the class. 2. Default: The access level of a default modifier is only within the package. It cannot be accessed from outside the package. If you do not specify any access level, it will be the default. 3. Protected: The access level of a protected modifier is within the package and outside the package through child class. If you do not make the child class, it cannot be accessed from outside the package. 4. Public: The access level of a public modifier is everywhere. It can be accessed from within the class, o

 Introduction      A java package is a group of similar types of classes, interfaces and sub-packages. Package in java can be categorized in two form, built-in package and user-defined package. There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc. Here, we will have the detailed learning of creating and using user-defined packages. Simple example of java package The package keyword is used to create a package in java. //save as Simple.java   package mypack;   public class Simple{    public static void main(String args[]){       System.out.println("Welcome to package");      }   }   How to access package from another package? There are three ways to access the package from outside the package. 1. import package.*; 2. import package.classname; 3. fully qualified name. 1. Using packagename.*      If you use package.* then all the classes and interfaces of this package will be accessible but not subpackages. The import keyword is used to

Introduction        An interface in Java is a blueprint of a class. It has static constants and abstract methods. The interface in Java is a mechanism to achieve abstraction. There can be only abstract methods in the Java interface, not method body. It is used to achieve abstraction and multiple inheritance in Java. In other words, you can say that interfaces can have abstract methods and variables. It cannot have a method body. Java Interface also represents the IS-A relationship.      It cannot be instantiated just like the abstract class. Since Java 8, we can have default and static methods in an interface. Since Java 9, we can have private methods in an interface. There are mainly three reasons to use interface. They are given below 👉 It is used to achieve abstraction. 👉 By interface, we can support the functionality of multiple inheritance. 👉 It can be used to achieve loose coupling. Declaration of interface: An interface is declared by using the interface keyword. It provides

Introduction      A class define using abstract keyword is called Abstract class . Abstraction is a process of hiding the implementation and provide the functionality to user in other word it hide the details and show only functionality. The genreal example is SMS function in mobile. We dont know actualy how it work but we know how to use it. There are two way to archive abstraction. Abstract class Interface 1. Abstract Class:      A class define using abstract keyword is called  Abstract class . It have abstract and non-abstract both the method. It need to be extend and methods to be implemented. It cannot be instantiated. Main Points to remember: 👉 An abstract class must be declared with an abstract keyword. 👉 It can have abstract and non-abstract methods. 👉 It cannot be instantiated. 👉 It can have constructors and static methods also. 👉 It can have final methods which will force the subclass not to change the body of the method.      Abstract Methods: A method which is declare