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Interview Questions and Answers

HashSet is an unordered collection that does not allow duplicate elements. TreeSet is a sorted set that implements the SortedSet interface. HashSet uses a hash table for storage, providing fast retrieval. TreeSet uses a tree structure, which maintains elements in sorted order.

A Map is a collection that stores elements in key-value pairs. Each key is associated with a value. Maps do not allow duplicate keys. Examples include HashMap, TreeMap, and LinkedHashMap.

Serialization is the process of converting an objects state into a byte stream. This byte stream can then be stored in a file or transmitted over a network. Deserialization is the reverse process, where the byte stream is used to recreate the object.

Java annotations are a form of metadata that provide information about the code. They can be used to provide instructions to the compiler, tools, or runtime environment. Examples include @Override, @Deprecated, and custom annotations.

The final keyword has different meanings depending on where its used: final variable: The variables value cannot be changed after initialization. final method: The method cannot be overridden by subclasses. final class: The class cannot be subclassed (inherited from).

Lambda expressions are anonymous functions that can be treated as values. They provide a concise way to represent single-method interfaces (functional interfaces). Lambda expressions are often used with the Stream API to perform functional operations on collections.

The break statement is used to terminate the execution of a loop or switch statement. The continue statement skips the current iteration of a loop and proceeds to the next iteration.

An exception is an event that disrupts the normal flow of the programs execution. Exception handling in Java is done using try-catch blocks, optionally followed by a finally block. The try block contains the code that might throw an exception. The catch block handles a specific type of exception. The finally block contains code that is always executed, regardless of whether an exception is thrown or caught.

Checked exceptions are exceptions that the compiler forces you to handle (either by catching them in a try-catch block or declaring that the method throws them). Unchecked exceptions (RuntimeExceptions and Errors) are not required to be handled by the compiler.

Multithreading is the ability of a program to execute multiple threads concurrently. In Java, multithreading can be achieved by either extending the Thread class or implementing the Runnable interface.

When you extend the Thread class, you inherit its properties, but you cannot inherit from another class. Implementing the Runnable interface allows you to inherit from another class while still being able to create a thread. Implementing Runnable is generally preferred because it promotes loose coupling and adheres to the principle of composition over inheritance.

A Java Collection is a framework that provides a unified architecture for storing and manipulating a group of objects. It includes interfaces and classes for various data structures like lists, sets, and maps.

ArrayList is an array-based list that provides fast random access to elements. LinkedList is a linked-list based list where elements are linked together. ArrayList is generally faster for accessing elements by index, while LinkedList is generally faster for inserting or deleting elements in the middle of the list.

Java has two categories of data types: primitive and non-primitive (reference) data types. Primitive data types include byte, short, int, long, float, double, boolean, and char. Non-primitive data types include classes, interfaces, arrays, and String.

Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects," which contain data and code: data in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods). The four main principles of OOP are: Encapsulation, Abstraction, Inheritance, and Polymorphism.

Encapsulation: Bundling data (attributes) and methods that operate on that data within a single unit (class). Abstraction: Hiding complex implementation details and showing only essential information to the user. Inheritance: A mechanism where a new class (subclass/child class) inherits properties and behaviors from an existing class (superclass/parent class). Polymorphism: The ability of an object to take on many forms.

The == operator compares the memory addresses of two objects (reference equality). The .equals() method, by default, also compares memory addresses, but it can be overridden in a class to compare the content of the objects (value equality).

Java has four main types of loops: for loop, while loop, do-while loop, and enhanced for loop (for-each loop).

Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. Key features include platform independence (Write Once, Run Anywhere), object-oriented programming, automatic memory management (garbage collection), multithreading, and strong exception handling.

JVM (Java Virtual Machine) is the engine that executes Java bytecode. JRE (Java Runtime Environment) provides the runtime environment in which Java programs can be executed. JDK (Java Development Kit) is a complete development package that includes the JRE, compilers (like javac), debuggers, and other tools necessary to develop Java applications.