Java Interview Questions and Answers

Doing well on a Java interview can be the difference between a job offer and a lifetime of disappointment. Preparation is essential and knowing the right questions to ask and the answers to give can help you to put your best foot forward. This article looks at 50 of the most common Java interview questions that you should be prepared to answer.

What are the features of Java?

Java is internationally renowned for its ability to allow developers to create applications that are both powerful and easy to use. It is an object-oriented programming language with several features that make it unique. Some of these features include:

  •  Compiled and Interpreted Language: Java is both a compiled and interpreted language, meaning that applications written in Java are compiled into bytecode and then interpreted by the Java Virtual Machine (JVM). This makes it easier to create applications that are platform-independent and can be run on any operating system.
  •  Object-Oriented: Java is a full-fledged object-oriented programming language. It has features such as classes, objects, inheritance, encapsulation, and polymorphism. This makes it easier for developers to create complex applications with fewer lines of code.
  •  Memory Management: Java has an automated garbage collection mechanism, which makes it easier for developers to manage memory and keep applications running smoothly.
  •  Secure: Java is a secure language, which makes it ideal for applications that need to protect sensitive data or user information. The Java Virtual Machine has a built-in security manager, which helps to protect applications from malicious code.
  •  Multi-Threading: Java supports concurrent execution of multiple threads, allowing developers to create applications that can take full advantage of multi-core processors.

What is the difference between a JDK and a JVM?

The JDK (Java Development Kit) and JVM (Java Virtual Machine) are two components of the Java platform. The JDK is a software development environment for writing, compiling, and running Java programs. It includes the JVM, a set of libraries, and various development tools such as the Java compiler and debugger.

The JVM is an abstraction layer that allows Java applications to run on any operating system or platform. It is responsible for interpreting and executing bytecode, which is generated when a Java program is compiled.

What is the difference between a String and a StringBuffer?

The String and StringBuffer classes in Java are both used to represent text in a program. The main difference between the two is that a String is an immutable class, while a StringBuffer is a mutable class.

An immutable class cannot be changed once it has been created. This means that when you concatenate two Strings or change the value of one, a new String object must be created.

A StringBuffer, on the other hand, can be modified without creating a new object. It also has several methods that allow developers to easily manipulate strings, such as the append(), insert(), and delete() methods.

What is the difference between a HashMap and a Hashtable?

The HashMap and Hashtable classes are both used to store and retrieve data in Java. The main difference between the two is that a HashMap is not thread-safe, while a Hashtable is.

A HashMap does not guarantee that the order of the elements will remain constant over time. It also does not implement any locking mechanisms, which makes it vulnerable to race conditions.

A Hashtable, on the other hand, is thread-safe and does not allow for race conditions. It also guarantees that the elements will remain in the same order. However, it is less efficient than a HashMap because of the overhead associated with thread-safety.


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