Top 10 JAVA Questions that can help you ace your interview

1. What is the difference between Overloading and Overriding?

When you have two methods with exactly similar names but different properties, then we call it Overloading. On the other hand, Overriding refers to a condition when two methods with identical names and properties exist, but the two are present in a parent and child class respectively.

2. What do you mean by a Singleton Class?

A singleton class can only have one object at a time. In other words, a singleton class can have only a single instance of a class.

It only permits one instance of itself to be constructed and provides access to that instance. It has static variables that may be used to create unique and private instances of itself. It's used when a user wishes to limit the number of objects that may be instantiated by a class. This becomes essential when a single item is necessary to coordinate operations throughout a system.

3. How are JVM, JRE, and JDK different?

JVM (Java Virtual Machine): The JVM (Java Virtual Machine) is a run-time engine that allows Java programs to run. JVM is the module that executes the main function in Java programming. JVM is a part of JRE.

JRE (Java Runtime Environment): A runtime environment in which Java bytecode may be executed is referred to as a JRE. It creates the JVM (Java Virtual Machine) and all of the class libraries and other support files that the JVM needs to execute. As a result, JRE is a software package that includes everything needed to run a Java program. In a nutshell, it's a physical implementation of the Java Virtual Machine.

JDK(Java Development Kit): It's the utility required for compiling, documenting, and packaging Java projects. JDK comprises the Java Runtime Environment (JRE), which offers resources for Java developers and is available for free. It contains an interpreter/loader, a compiler (javac), an archiver (jar), a document creator (JavaDoc), and other Java development tools in addition to JRE.

4. What is Constructor Chaining?

Constructor chaining is the sequence of executing constructors when an object is created in Java. It's useful when we want to call a series of constructors one after the other with just one instance. Constructor chaining happens as a result of inheritance. The inheritance chain might contain any number of classes.

On creating an instance of the derived class, the constructors initially invoked belong to the inherited or base class. Following this, the constructors of the derived or calling class are invoked.

5. What is Object Cloning?

Object cloning, as the name suggests, refers to the process of creating a copy of the existing object. In order to sustain object cloning, a class would need to implement the java.lang.Cloneable interface and override clone() method from the Object class.

The syntax of the clone()method is :

protected Object clone() throws CloneNotSupportedException

The exception ‘CloneNotSupportedException' is thrown if the class of the object being cloned, does not implement the Cloneable interface.

6. What are Collections in JAVA?

In Java, a collection is a framework that allows you to store and modify a set of objects. All data actions, including searching, sorting, insertion, mutation, and deletion, can be accomplished using Java Collections. An assemblage of different objects to demonstrate a single unit is known as the Collection. The two major interfaces of Java Collections are the Collection Interface (java.util.Collection) and Map Interface (java.util.Map)

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7. What do you mean by JAVA interfaces?

According to Oracle, an interface can be defined as a group of associated methods with empty bodies. It is the blueprint of a class that possesses abstract methods. Interfaces provide a mechanism to implement abstraction in JAVA meaning an interface can only have abstract methods and no method body.

Java Interface also represents the IS-A relationship.

8. Define the underlying concepts of OOP (Object Oriented Programming)

Object-Oriented Programming is the foundation of today’s development world. The programming paradigm is being followed everywhere today. JAVA, being an object-oriented programming language, demands strong OOPs concepts for any developer. Here are the underlying principles of OOPs:

• Encapsulation
• Abstraction
• Inheritance
• Polymorphism

Clear understanding and distinction between the OOPs principles are essential.

9. What is the Static keyword in JAVA?

In Java, the static keyword is used to control memory. For methods and attributes, the static keyword is a non-access modifier. Methods and attributes of static type can be invoked without constructing an object of the class. The static keyword in JAVA can be applied to variables, methods, blocks, nested classes, etc.

The following programming constructs can be Static:

• Variable
• Method
• Block
• Nested Class

10. On a Scale of 10 — Where would your JAVA skills stand?

The aim behind this question is not to judge your JAVA proficiency, but to check the level of self-awareness you possess. Ideally, you should always cite a grade that is less than the actual benchmark that defines your capability. The Reason? Since the difficulty of questions asked will always be on the higher end of difficulty.

Before you go to the interview…

Before you go to the interview make sure that you have the basics right. Dress smartly, carry yourself with confidence and be true to yourself. Don’t try to fake anything, the people on the other side are smart enough to catch your bluffs. A simple ‘No’ is better than the built-up stories. So make sure that you answer all the questions accurately and precisely.

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