Top 10 Java Position Interview Questions and Answers [Updated 2024]

Sample Answer
An abstract class in Java is a class that can’t be instantiated and is typically used as a base class for other classes to inherit from. They can have both abstract (method declared without implementation) and non-abstract methods (methods with implementation). An interface, on the other hand, is basically a template for a class. It can only declare fields and methods, and methods are by default abstract. Classes ‘implement’ interfaces, thus inheriting the methods declared in the interface.

Sample Answer
Java Collections Framework provides a well-designed set of interfaces and classes that support operations on a collections of objects. They are used in almost every application. Java Collections can achieve all the operations that you perform on a data like searching, sorting, insertion, manipulation, and deletion. Java Collection means a single unit of objects and it includes classes like List, Set, and Map.

Sample Answer
Java is platform-independent, meaning the same code can run regardless of the operating system or the architecture of the device, due to the JVM (Java Virtual Machine). Furthermore, Java’s object-oriented programming allows for reusable code and modular programs. Java also has automatic memory management, which helps to avoid memory leaks.

Sample Answer
Exception handling in Java provides a way to process or handle the exception so that normal flow of the application can be maintained. It involves five keywords: try, catch, finally, throw, and throws. The ‘try’ block is used to enclose the code that might throw an exception. The ‘catch’ block is used to handle the specific exception type. The ‘finally’ block is a block that always executes whether exception is handled or not.

Sample Answer
Multithreading in Java is a feature that allows concurrent execution of two or more parts of a program for maximum utilization of CPU. Threads are independent, they don’t affect the execution of other threads. An exception in one thread will not interrupt other threads. It’s used in games, animation, etc.

Sample Answer
Object Oriented Programming (OOP) is a programming paradigm that is based around the concept of ‘objects’. Objects are components of a program that contain both data and operations that manipulate that data. The main principles of OOP are Encapsulation, Inheritance, Polymorphism, and Abstraction. Encapsulation is the technique of making the fields in a class private and providing access to the fields via public methods. Inheritance is a mechanism wherein a new class is derived from an existing one. Polymorphism allows us to perform a single action in different ways. Abstraction is the process of hiding certain details and showing only essential information.

Sample Answer
‘final’ is a keyword, ‘finally’ is a block and ‘finalize’ is a method. ‘final’ keyword can be used with variables, methods and classes. A ‘final’ variable value can’t be changed, a ‘final’ method can’t be overridden and a final class can’t be subclassed. ‘finally’ block is optional and can be used only with try-catch to put the critical code, it will execute whether an exception is thrown or not. ‘finalize’ is a method that garbage collector calls just before the object is being collected.

Sample Answer
The ‘static’ keyword in Java is used primarily for memory management. It is used with variables, methods, blocks and nested classes. If you make any variable as static, it is known as a static variable. The static variable can be used to refer to the common property of all objects (which is not unique for each object). If you make any method as static, it is known as a static method. A static method belongs to the class rather than the object. A static method can be invoked without the need for creating an instance of a class. Static methods cannot use class instance variables or call instance methods.

Sample Answer
Garbage Collection in Java is the process of reclaiming the unused memory space and making it available for future instances. The Garbage collector thread performs this operation. The main advantage of garbage collection is that it automatically handles the deletion of unused objects or the memory space cleaning, to free up memory. This automation removal of unused objects means that the programmer need not to worry about memory deallocation.

Sample Answer
The Singleton pattern ensures that a class has only one instance, and provides a global point of access to it. In essence, a Singleton is a class which only allows a single instance of itself to be created, and usually gives simple access to that instance. Implementing the Singleton pattern involves creating a static method that returns the instance of the class, making the constructor of the class private to prevent instantiation, and creating a static variable of the Singleton type.