Java Interview Questions For 6 Years Experience
Top Interview Questions for Java Professionals with 6 Years of Experience
Java is a popular programming language used in enterprise software development. For candidates with 6 years of experience, interview questions will focus on their depth of knowledge and practical experience in Java programming, data structures, algorithms, design patterns, and experience with popular frameworks and libraries. It is also expected that candidates have a good understanding of object-oriented programming principles and can demonstrate their ability to write efficient, scalable, and maintainable code. Additionally, they may be asked about their experience with troubleshooting and debugging, as well as their knowledge of best practices and industry standards. Employers are looking for candidates who not only have strong technical skills but also have the ability to communicate effectively and work well in a team.
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1 - What is the difference between String, StringBuilder and StringBuffer?
StringBuilder and StringBuffer are mutable whereas String is immutable. This means that StringBuilder and StringBuffer can be modified, whereas String remains the same and any changes to it result in a new String object being created. StringBuilder and StringBuffer also have a higher performance than String as they do not need to create new objects every time they are modified. StringBuffer is thread-safe, while StringBuilder is not.
2) Can you explain the concept of polymorphism in Java?
Polymorphism refers to the ability of different types of objects to be treated similarly, while also behaving according to their specific types. This can be achieved in Java through method overloading and method overriding. Method overloading means having multiple methods with the same name but different parameters, while method overriding means having a method in a child class with the same name and signature as a method in the parent class, allowing for different behavior based on the specific subclass.
3) What is the difference between an interface and an abstract class?
An interface is a collection of abstract methods without any implementation, whereas an abstract class is a class that can contain both abstract and non-abstract methods. An interface can be implemented by multiple classes, while a class can only extend one abstract class. Interfaces are used to achieve abstraction and provide a common contract for multiple classes, while abstract classes are used to provide a common base for related classes.
4) Can you explain the concept of exception handling in Java?
Exception handling in Java refers to the process of dealing with errors and exceptions that may occur during the execution of a program. This is done using try-catch blocks where any code that may throw an exception is put inside a try block and the corresponding catch block is used to catch and handle the specific exception. This ensures that the program does not crash and allows for graceful handling of errors.
5) What is the difference between a class and an object?
A class is a blueprint or template for creating objects, while an object is an instance of a class. A class can contain attributes (variables) and methods (functions), while an object is a specific representation of those attributes and methods. A class can be thought of as a cookie cutter, while an object is the actual cookie created from that cutter.
6) What is the difference between a constructor and a method?
A constructor is a special method that is automatically called when an object is created and is used to initialize the attributes of the object. It has the same name as the class and does not have a return type. On the other hand, a method is a function that performs a specific task and can be called on an object. It has a return type and may or may not take in parameters.
7) Can you explain the different types of inheritance in Java?
Inheritance is a mechanism in Java that allows a child class to inherit properties and methods from a parent class. There are three types of inheritance: single inheritance, where a class inherits from a single parent class, multiple inheritance, where a class inherits from multiple parent classes, and multilevel inheritance, where a class inherits from a parent class, which in turn inherits from another parent class.
8) What is the difference between a static variable and a non-static variable?
A static variable is a class-level variable that is shared among all instances of the class, while a non-static variable is an instance-level variable which is unique to each instance of the class. Static variables are also called class variables and can be accessed without creating an object of the class, while non-static variables can only be accessed through an instance of the class.
9) What is the purpose of the “static” keyword in Java?
The “static” keyword can be used for both variables and methods in Java. For variables, it indicates that the variable is a class variable and can be accessed without creating an object of the class. For methods, it indicates that the method is a class method and can be called without an instance of the class. Static methods are commonly used for utility methods that do not require any specific instance data.
10) What is the difference between a deep copy and a shallow copy?
A deep copy creates a separate copy of an object with its own set of values, while a shallow copy creates a new object, but its attributes still refer to the same objects as the original. In other words, a deep copy creates a complete, independent copy, while a shallow copy creates a copy that is partially independent.
11) Can you explain the concept of encapsulation in Java?
Encapsulation is the process of wrapping data and methods into a single unit, known as a class, and controlling access to that data through methods. This allows for data hiding, as the internal details of the class are hidden from the outside world, and can only be accessed through its methods. Encapsulation helps to achieve data abstraction and improves the security and maintainability of code.
12) What is the difference between a Set and a List?
A Set is an unordered collection of unique elements, meaning that it does not allow duplicates. It is implemented by the HashSet and TreeSet classes. On the other hand, a List is an ordered collection that allows duplicates and maintains the insertion order. It is implemented by the ArrayList and LinkedList classes.
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13) What is a HashMap in Java?
A HashMap is a data structure that stores key-value pairs, similar to a Dictionary in Python. It uses hashing to store and retrieve elements and thus has a very efficient lookup time. Duplicate keys are not allowed in a HashMap, but values can be duplicated.
14) What is the difference between a stack and a queue?
A stack is a data structure that follows the LIFO (Last In First Out) principle, where the last element added is the first one to be removed. This is analogous to a stack of plates. On the other hand, a queue follows the FIFO (First In First Out) principle, where the first element added is the first one to be removed. This is analogous to a line of people waiting at a ticket counter.
15) Can you explain the concept of synchronization in Java?
Synchronization in Java refers to the process of controlling the access to shared resources by multiple threads in a multi-threaded environment. This is done using the synchronized keyword so that only one thread can access the resource at a time, ensuring data consistency and avoiding race conditions. It is commonly used when accessing shared objects or updating shared variables.
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