In today’s competitive world, everyone is ambitious for securing a high-paying job. A career in Java is the most sought-after in this technology world. To get into your dream job, the first and the foremost hurdle to achieve is - Cracking an Interview with confidence.
This article covering almost everything about Core Java interview questions will help you in revising for entry-level as well as experienced developers. The Core Java Interview Questions are prepared by our most experienced experts in the industry. This questionnaire will substantially contribute to achieving your dream job.
"Core Java" is a general term used by Sun Microsystems to describe the standard version of Java (JSE). It’s the most basic version of Java which sets the foundation for all other editions of Java plus a set of related technologies such as CORBA, Java VM, Java Naming and Directory Interface (JNDI), Tools API, etc. Core Java refers to a collection of libraries rather than just the programming language. It’s the purest form of Java primarily used for the development of general desktop applications. Simply speaking, it refers to the subset of Java SE technologies which consists of both general-purpose API and special-purpose APIs. It provides the core functionality of Java with the deep knowledge of the Java language itself.
Core Java is just a part of Java which stands for J2SE containing all the basics of Java including some principles and package details. It’s a stand-alone Java application that covers everything from OOP concepts to special operators, from data types to wrapper classes, from the Linked list to Array list, and queue to exception handling. There are three computing platforms based on the Java programming language, including the Java SE. It still is the most widely used platform based on the concept of OOP and is commonly used for the development of portable desktop applications. In addition to the general-purpose APIs, it consists of development tools, a virtual machine, and other class libraries. It also includes the Java Virtual Machine Specification.
The concepts from core Java are - OOPS concepts (Data Abstraction, Encapsulation, Inheritance, Polymorphism), Basic Java constructs like loops and data types, String handling, Collection framework, Multithreading, Exception Handling, Generics, Synchronization.
Java is the high-level, object-oriented, robust, secure programming language, platform-independent, high-performance, Multithreaded, and portable programming language. It was developed by James Gosling in June 1991. It can also be known as the platform as it provides its own JRE and API.
Platform independence means that we can write and compile the java code in one platform (eg Windows) and can execute the class in any other supported platform eg (Linux, Solaris, etc).
JVMs are not platform-independent. JVMs are platform-specific run time implementation provided by the vendor.
JVM is Java Virtual Machine which is a run time environment for the compiled java class files.
JDK is Java Development Kit that is for development purposes and it includes an execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.
A pointer is a reference handle to a memory location. Improper handling of pointers leads to memory leaks and reliability issues hence Java doesnt support the usage of pointers.
Java doesnt support multiple inheritances.
Java uses primitive data types and hence is not a pure object-oriented language.
In Java, Arrays are objects.
Path and Classpath are operating system-level environment variables. The path is used to define where the system can find the executables(.exe) files and classpath is used to specify the location of .class files.
Local variables are those which are declared within a block of code-like methods. Local variables should be initialized before accessing them.
Instance variables are those which are defined at the class level. Instance variables need not be initialized before using them as they are automatically initialized to their default values.
The variable should be declared as static and final. So only one copy of the variable exists for all instances of the class and the value cant be changed also. static final int PI = 2.14; is an example for constant.
No not required. the main method should be defined only if the source class is a java application.
The main method doesnt return anything hence declared void.
the main method is called by the JVM even before the instantiation of the class hence it is declared as static.
It is a programming paradigm based on objects having data and methods defined in the class to which it belongs. The object-oriented paradigm aims to incorporate the advantages of modularity and reusability. Objects are the instances of classes that interact with one another to design applications and programs. There are the following features of the object-oriented paradigm.
The Object is the real-time entity having some state and behavior. In Java, an object is an instance of the class having the instance variables like the state of the object and the methods as the behavior of the object. The object of a class can be created by using the new keyword.
There are the following basic differences between object-oriented language and object-based language.
All object references are initialized to null in Java.
The constructor can be defined as the special type of method that is used to initialize the state of an object. It is invoked when the class is instantiated, and the memory is allocated for the object. Every time, an object is created using the new keyword, the default constructor of the class is called. The name of the constructor must be similar to the class name. The constructor must not have an explicit return type.
Based on the parameters passed in the constructors, there are two types of constructors in Java.
yes, The constructor implicitly returns the current instance of the class (You cant use an explicit return type with the constructor).
No, The constructor is not inherited.
No, the constructor cant be final.
Yes, the constructors can be overloaded by changing the number of arguments accepted by the constructor or by changing the data type of the parameters. Consider the following example.
In the above program, The constructor Test is overloaded with another constructor. In the first call to the constructor, The constructor with one argument is called, and I will be initialized with the value 10. However, In the second call to the constructor, The constructor with the 2 arguments is called, and I will be initialized with the value 15.
Two main restrictions are applied to the static methods.
There are a lot of career opportunities for Core Java talent. Once you get a sound knowledge about Java, it will open all doors for learning lots of tools and technology around Java. Java is the best choice when coming to working with various domains and high pay packages.
Most of the reputed companies like Google, Amazon, IBM, Infosys, CTS, and TCS, etc. are using java as their preferred Programming Language. Java Programmer Salary in the technology industry is one of the most lucrative in this world. The average pay for a Java Programmer is around $67,129 per year. Experience strongly influences income for this job segment. The average salary for an experienced Java Developer in the USA is more than $102,000. For entry-level developers, salaries are still extremely competitive and often far higher than other entry-level roles.
So here’s the good news, our article on Core Java Interview Questions has been designed specially to get you acquainted with the nature of questions you may encounter during your interview. We have covered an entire variety of Core Java Interview Questions and answers which will eventually help you qualify for the interview and provide you with a successful career outlook. We wish you all the best in your professional career and will be glad to help you with any queries related to Core Java Interview questions.