Core Java

JAVA is one of the most popular programming languages. It was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun Microsystems, Inc. in 1991. It was publicly released in 1995. Now, Oracle has acquired Sun Microsystems, so all Java certifications are provided by Oracle.

Java is an object-oriented, high-level language used to develop web, mobile, and standalone applications.

Its main features are:

• Platform Independence
• Security
• Orientation: This refers to a way of thinking in terms of objects. Based on this perspective, a programming model called Object-Oriented Programming (OOP) is created. This model simplifies software development and maintenance with the following concepts:

OOP’s Basic Concepts:

• Object
• Classification
• Generalization & Inheritance
• Polymorphism
• Data Encapsulation

Object: An object is a discrete entity with well-defined attributes and behaviors. It can be a physical thing or an abstract concept.

Classification: Classification is the process of grouping objects with common attributes and behaviors into a logical unit called a class. The concept of classification simplifies object management.

Generalization: Generalization is a process of abstraction where common features of classes are abstracted to simplify their management. The concept of generalization simplifies the management of classes. Inheritance is the means of implementing generalization.

Polymorphism: Polymorphism in programming states that behaviors can manifest in different ways. There are two aspects of polymorphism:

1. One object manifests behavior in different ways.
2. Different objects manifest the same behavior in different ways.

Behavior is implemented as methods, which need to be named. A method can be named based on the behavior or its manifestation. Hence, identification is simplified by naming the method based on the behavior. The concept of polymorphism simplifies the management of behaviors.

Encapsulation: Encapsulation deals with the protection of data from accidental or unintentional corruption by the programmer. This concept states that the scope of data must be confined within a logical unit called a class. Data of one class must not be accessed directly from another class. Any programming language that provides the implementation of these five concepts is called an Object-Oriented Programming Language.

Difference Between Method and Function: The term “function” represents a task, whereas the term “method” represents behaviors.

Anonymous Block (init block): An anonymous block is a block of statements that doesn’t have a name associated with it. Init blocks are used in the case of overloaded constructors to define common statements for all constructors. If there is more than one init block in a class, their statements are grouped in the order of their occurrence in the class before they move to the constructor.

Static Keyword: The static keyword is used to define class members. In a class, there can be the following class members:

• Static data member: Represents class attributes that are common to all objects of the class. Only a single copy of a static data member is created at the time of class loading, and this single copy is shared by all objects of the class.
• Static block: A block of statements that is executed on its own just after a class is loaded. It represents the initialization of a class and is used to initialize static data members of a class.

static {

    // statements to be executed at the time of class loading

}

• Static methods: Represent the behavior of a class and are invoked using the class name.

Final Keyword in Java: The final keyword is similar to the const keyword in other languages. It is used to restrict the user and can be used in various ways:

• Variable
• Method
• Class

Final Variable: Used to declare a constant value which, once assigned, cannot be changed further.

Final Method: A final method cannot be overridden by a subclass. This prevents unexpected behavior in the class. 

    Note: Private and static methods are always implicitly final in Java, as they cannot be overridden.

Final Class: A final class cannot be extended by any other class. Implicitly, all methods of a final class are declared as final, but not its data members. Final methods are inherited but cannot be overridden.

This Keyword In Java:

• this keyword keyword is used to refer to the current object.
• this is always a reference to the object on which the method was invoked.
• this can be used to invoke the current class constructor.
• this can be passed as an argument to another method.

 Example:

public class Box {

Double width, height, dept;

public Box(double w, double h, double d ) {

              this.width = w;

              this.height = h;

              this.dept = d;

}

}

Here, this is used to initialize members of the current object.
this is also used to call an overloaded constructor in Java.

public class Car {

private String name;

public Car() {

this("BMW");   // overloaded constructor is called.

}

public Car(String n) {

this.name = n;    // member is initialized using this.

}

}

The this is also used to call Method of that class.

public void getName() {

      System.out.println("TechA2ZSolution");

}

public void display() {

      this.getName();

      System.out.println();

}

this is used to return current Object

public Car getCar() {

        return this;

}

Super Keyword in Java

The super keyword in Java is a reference variable which is used to refer to the immediate parent class object. Whenever you create an instance of a subclass, an instance of the parent class is created implicitly, which is referred to by the super reference variable.

Usage of Java super Keyword

• super can be used to refer to the immediate parent class instance variable.
• super can be used to invoke the immediate parent class method.
• super() can be used to invoke the immediate parent class constructor.

Read More Here...

• Java Getting Started
• Operators in Java
• Conditional Statements & Loops in Java
• Java Class And Object
• Java Constructor
• Java Basics
• Static in Java
• Array in Java
• Java Math
• OOPS Concepts
• Interface in Java
• String in Java
• Java Exception handling

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