Java Interview Questions and Answers

Why Java? 

Java is a computer programming language and platform. It ranks first among all programming languages and offers a diverse range of work prospects. The basic strength of Java, and the reason why many developers program in it, is that it is simple to write and run. You can run Java practically anywhere at any time after you've written it. A developer will be able to write code quickly after they are comfortable with installing JDK, setting up PATH, and understanding how CLASSPATH works.

There's a lot you can do with Java, and there are libraries for practically anything. There are better GUI (Graphical User Interface) systems available in Java than the basic AWT and Swing libraries.

JDBC can also be used to connect to databases (Java Database Connectivity).

For these reasons, the developer community is proven to be the language's and platform's strength. Without a community to support, help, and share their knowledge, a programming language would perish.

The Java programming language community continues to expand and inspire with tens of millions of developers using and working on it.

When to use Java

Java may be used to build full apps that can run on a single computer or across a network of servers and clients. As a result, you can use it to quickly create mobile apps or desktop apps that run on a variety of operating systems and servers, including Linux and Windows.

Access specifiers for Java classes

In Java, access classifiers are keywords that are used before a class name to refer to the access scope. The access classifiers listed below are quite significant and are commonly asked Java Interview Questions.

• default: field, method, and class can only be accessible from within the native package, not from outside. public: a field, method, or class can be accessed from any location.

• protected: fields and methods can only be accessible from within the same class, subclasses, and within the same package class, but not from outside.

• private: field, the method can only be accessed from inside the same class.

Java Features

Features of Java are as follows:

• OOP concepts

  • Object-oriented: Object-oriented programming is a programming method that uses classes and objects to construct a program. Object-oriented programming is also known as Java's core.

  • Inheritance: Inheritance refers to the ability for one class to extend to another in order for the coding to be reused from one class to the next. The existing class is referred to as a Superclass, whereas the derived class is referred to as a Subclass.

  • Encapsulation: In Object-Oriented Programming, encapsulation is a technique for merging methods and properties into a single unit. Because each object has its own set of variables and methods and serves its functions independently of other objects, encapsulation aids programmers in taking a modular approach to software development. Encapsulation can also be used to hide data.

  • Polymorphism: Polymorphism refers to the fact that something exists in multiple forms. Polymorphism is the ability of a single object to refer to either a super-class or a sub-class, depending on the reference type.

  • Data abstraction: The practice of reducing an entity to its core so that the necessary properties are accessible to consumers is known as abstraction. Abstraction describes an object by its properties (attributes), as well as its behavior (methods) and interfaces (means of communicating with other objects).

• Platform independence: A single software can run on a variety of systems without needing to be modified.

• High-Performance: The JIT (Just In Time) compiler in Java allows for high performance. JIT translates the bytecode to machine language before the JVM executes it.

• Multi-threaded: A Thread is a type of execution flow. The JVM creates a thread known as the main thread. By extending the thread class or implementing the Runnable interface, the user can construct many threads.

Loops in Java

In programming, looping is a technique for repeatedly executing a statement or a statement block. In Java, there are three types of loops:

a. For Loops: In Java, loops are used to repeat statements for a set number of times. When the number of times to implement the statements is referred to the programmer, loops are employed.

b. while Loops: A while loop is used when certain statements must be executed regularly until a condition is met. Before statements in while loops are implemented, the condition is tested first.

c. Do While Loops: A do-while loop is similar to a while loop with the exception that the condition is reviewed after the statement blocks are implemented. Consequently, in a do-while loop case, statements are executed at_least once.

Constructor in Java

A constructor can be elucidated in detail with enlisted points:

• When a new object is formed and called in a program, a constructor gets invoked corresponding to the class.

• The constructor is a method that has an identical name to the class name.

• If a user doesn’t create a constructor implicitly, a default constructor will be formed and called.

• The constructor can_be overloaded.

• If the user created a constructor with a parameter, they should create an alternative constructor explicitly without a parameter.

Objects and classes in Java

An object is a representation of a class instance. The object has a state and behaves in a certain way. When the JVM encounters the keyword "new()," it will generate a new instance of that class.

A Class is where all Java code is defined. There are variables and methods in it. Variables are attributes that specify a class's state. Methods are where the precise business logic must be implemented. It consists of a series of statements (or) instructions that must be followed to meet the specific requirement.

Java Packages and their significance

In Java, a package is a collection of interfaces and classes packed together because they are related to one another. The usage of packages allows developers to modularize their code and assemble it for re-use. After the code has been packaged, it can be imported and used in other classes.

About this course

Java is a general-purpose programming language. Java is used on mobile phones, desktop computers, and large-scale industry servers and applications because of its stability and scalability.

Java has recently gained popularity in the Internet of Things (IoT) and cloud development fields.

Because technology is growing rapidly, there are a plethora of potential job prospects, and Java developers are in high demand.

The Java programming language, which already has a large user base, provides numerous jobs in the computer industry.

As a result, this course will teach you how to confidently and comfortably answer complex java interview questions.

All the best to you and have a Great Learning!!!