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Access Modifiers in Java

 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
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Java Package

 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
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Interface in Java

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
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Abstract in java

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
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Super and Final keyword

  Super Keyword      The super keyword in java is a reference varible which is use to refer immediate parent class instance variable . Super can use to invoke immediate parent class method and constructors also. 1. To Refer Instance variable of an immediate parent class:      We can use super keyword to access the data member or field of parent class. It is used if parent class and child class have same fields. For example, class Animal{   String color="white";   }   class Dog extends Animal{   String color="black";   void printColor(){   System.out.println(color); System.out.println(super.color); }   }   class TestSuper1{   public static void main(String args[]){   Dog d=new Dog();   d.printColor();   } } Output: black white 2. To Refer method of an immediate parent class:      The super keyword can also be used to invoke parent class method. It should be used if subclass contains the same method as parent class. In other words, it is used if method is overri
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Polymorphism, Method overloading and Method Overriding

 Introduction of Polymorphism     Polymorphism is the concept by which we can perform single action/operation in different ways. In other word ability to tae more than one form called polymorphism .     Polymorphism plays an important role in allowing objects having different internal structure to share same external interface. That means the general class of operation may be access in same manner but the specified action with each operation may be different. Ploymorphism is use in implementing inheritance. There are two types of polymorphism in java those are as follows: Compile-time polymorphism. Runtime polymorphism.     We can perform polymorphism using method overloading and method overrding. 1. Compile-time polymorphism:     We can achive the compile time polymorphism using function/method overloading concept . When there are multiple function with the same name but having different parameter list or parameter then it is called function/method overloading . We can overload a fun
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Inheritance in java

 Introduction     If the one object can acquires all the properties and behaviour of parent object then it's called  Inheritance . The idea behind inheritance concept is, we can create a new class which is build upon existing one so we can reuse the methods and field of the parent class and also create new method in child class. Inheritance is use for method overriding and code reusability concepts. To create new child class from parent class we use the extends keyword. Syntax of define inheritace is as follow: class ChildClass extends ParentClass{     variable declaration;     method declaration; } There are different types of inheritance in java as follows: Single Inheritance. Multilevel Inheritance. Hierarchical Inheritance. 1. Single Inheritance:     A class/parent class inherits another class/child class is called Single inheritance . For example, class Animal{   void eat(){System.out.println("eating...");}   }   class Dog extends Animal{   void bark(){System.out.
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Static and this keyword

Static Keyword:      Most of the time static keyword in java use for memory management. We can use static keyword with variables, methods and also with block (Static block) . 1. Static with variables:     If we declare static keyword with variables then it's called static variables . Static variables are use to access or refer common properties of all objects. The static varibels gets memory only once at the time of loading class loading. It makes program more efficient i.e., It saves memory. For example,     static int length=100; 2. Static with method:     If we use static keyword with method then it's called static method . The static method is belong to class rather than object of class. Static method can invoke or call without creating instance or object of class. For example,     static void print(){          System.out.println("Welcome in Java");     } Examples of static variable, method and block is as follows: class Welcome{ static String textValue = "
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Java Classes, Object and Methods, Constructors

 Defining a class     A class is a user-defined data type or group of object with a template or blueprint that serves to define its properties. It is a logical entity. Once a class type has been define, we can create " Variables " which are similar to basic type declaration. In java, variables are termed as instance of class, which actual object. The basic form class defination is as follows: class classname [extends superclassname]{     [fields declaration]     [method declaration] } The classname and superclassname are valid java identifiers. The keyword extends indicate that superclassname properties extended into classname. It is a pert of inheritance. (We will discuss inheritance in later part.) Everything inside square brackets is optional that means we can use as per the requirements. For example, class Empty{ } In above example, the Empty class is class name. This class does not have any properties and therefor cannot do anything. A java class content:     Field or
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Jump Statements in java

    Introductions       Loopes perform a set of operations repeatedly until the control variable fails to satisfy the test condition. But in some times we need to skip some of the part of loop then we use the jump statements . For breaking the loop we use continue and break statement . Continue Statement:     When the continue statement called, it will break or stop the current itteration of loop on sameline and start the new iteration. Format of this statement is below:          continue; Brak Statement: After call this statement in the body of loop, it will sop or break the loop on current loop on same line and control goes to the next line after that loop. Format is below:     break; We mostly use this statement in while, do, and for loop concept.
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