Java - Intermediate

Question 1

JDK

Answer 1

JDK (Java Development Kit) is a software development environment that provides tools and libraries necessary for developing Java applications.

It includes the:
1. compiler,
2. debugger,
4. and other development utilities.

Question 2

JRE

Answer 2

• JRE (Java Runtime Environment)
• is an implementation of the JVM (Java Virtual Machine)
• along with libraries and other files required to run Java applications.

Question 3

JVM

Answer 3

• JVM (Java Virtual Machine)
• an abstract computing machine that executes Java bytecode.
• provides a runtime environment for Java applications (to run independently of the underlying hardware and operating system.)

Question 4

Explain the concept of polymorphism in Java

Answer 4

• it allows a subclass to override a method of its superclass, providing its own implementation.
• Polymorphism enables:
  1. code flexibility
  2. and reusability.

For Example:

class Shape {
    void draw() {
        System.out.println("Drawing a shape");
    }
}

class Circle extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a circle");
    }
}

class Rectangle extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a rectangle");
    }
}

public class Main {
    public static void main(String[] args) {
        Shape circle = new Circle();
        Shape rectangle = new Rectangle();

        circle.draw();     // Output: Drawing a circle
        rectangle.draw();  // Output: Drawing a rectangle
    }
}

Question 5

What are the different types of collections available in Java?

Answer 5

1. List
2. Set
3. Map
4. Queue

Question 6

List

Answer 6

1. Ordered
2. Allows duplicates

• Example:
  
  1. ArrayList,
  2. LinkedList

Question 7

Set

Answer 7

1. Unordered
2. Does not allow duplicates
   - Example:
   
   1. HashSet
   2. TreeSet

Question 8

Map

Answer 8

• An interface for a collection that stores data in key value pairs
• The way it orders depends on the implementation type:
  
  1. HashMap doesn’t guarantee order
  2. TreeMap sorts based on natural order of the keys
• Example:
  
  1. HashMap,
  2. TreeMap,
  3. LinkedHashMap,
  4. ConcurrentHashMap

Question 9

Queue

Answer 9

Follows the FIFO (First-In-First-Out) principle.

Question 10

Explain the concept of generics in Java

Answer 10

• Generics allow the use of type parameters to create generic classes and methods.
• provide compile-time type checking, ensuring that the correct types are used at compile time and preventing type-related errors at runtime

Question 11

What are the benefits of Generics?

Answer 11

• compile-time type safety,
• and thus preventing type-related errors at runtime

Question 12

ArrayList

Answer 12

ArrayList is the List implemented for a resizable array.

1. Dynamic Size
2. Can access elements by index
3. Ordered
4. Duplicates allowed
5. Null elements allowed
6. Resizes by a factor of 1.5 or 2

Question 13

LinkedList

Answer 13

1. double linked - knows prev and next node
2. dynamically sized
3. ordered
4. duplicates allowed
5. nulls allowed

Sequential access (walking the list) is better than random access.

Question 14

When should you use an ArrayList?

Answer 14

1. When you need fast access to elements by index
2. and when the list size doesn’t change frequently.

Question 15

When should you use LinkedLists?

Answer 15

1. When you need to add or remove an element from the beginning or end,
2. When you don’t know the size of the list you’re going to be working with.
3. When you will be frequently adding or removing elements from the list. (ArrayLists have to shift each element forward or backward in the list whereas a linked list only has to update it’s prev/next pointers).

Question 16

Explain the concept of threads in Java

Answer 16

1. A thread represents an independent path of execution within a program.
2. It allows multiple tasks to be executed concurrently.

Question 17

What is synchronization in Java?

Answer 17

Ensures that only one thread can access a shared resource at a time.

Question 18

Serialization

Answer 18

• object -> byte stream
• which can be stored in a:
  1. file,
  2. sent over a network,
  3. or persisted in a database.

Question 19

Deserialization

Answer 19

byte code -> object

Question 20

How do you serialize and desserialize a class?

Answer 20

• The Serializable interface is used to mark a class as serializable
• and the ObjectOutputStream is used to serialize an object
• and ObjectInputStream is used to deserialize an object.

Question 21

What are annotations in Java?

Answer 21

Annotations provide metadata about program elements, such as:
1. classes,
2. methods,
3. or fields.

Question 22

From Java 8 How do you handle dates and times in Java?

Answer 22

• In Java 8 and later versions, the Date and Time API (java.time package) was introduced.
• It provides classes like:
  1. LocalDate,
  2. LocalTime,
  3. LocalDateTime,
  4. and ZonedDateTime

for handling dates, times, and time zones.

Question 23

What are the advantadges of the Date and Time API in Java 8?

Answer 23

1. improved functionality,
2. immutability - once an object is created it’s state cant be changed
3. thread safety,
4. and better support for operations like
   
   1. parsing,
   2. formatting,
   3. and calculations.

Question 24

What are lambda expressions in Java?

Answer 24

1. anonymous functions
2. uses a more concise arrow syntax.
3. helpful for things like implementing Functional Interfaces (an interface with only one method) instead of using anonymous inner classes.

Question 25

Explain the concept of reflection in Java

Answer 25

Reflection is a feature in Java that allows you to examine and modify the structure and behavior of classes at runtime. It provides the ability to dynamically create new objects, invoke methods, and access fields, even for private members.

Question 26

What is a use case for reflection in Java?

Answer 26

- **Framework Dependency Injection**: Inspecting parameters in constructors and dynamically loading class instances. - **Framework Aspect Oriented Programming**: Identify and intercept method invocations on objects so that various aspects such as logging, exception handling, etc... can be dynamically applied at runtime.

Question 27

Explain the concept of dependency injection in Java

Answer 27

- Manage dependencies by **injecting them as parameters** in a constructor or method rather than creating them internally. - Helps achieve **loose coupling** between components promoting: 1. **easier testing** 2. and **maintainability**.

Question 28

What are the benefits of Dependency Injection?

Answer 28

1. Loose coupling 2. Improved reusability (used in more ways without having to change code). 3. Testability 4. Configurability (change configuration without changing the code) 5. Inversion of Control (allows for dependencies to be provided from an external source such as a framework allowing the code to focus on what it's supposed to do)

Question 29

Why should you use StringBuilder instead of concatenation?

Answer 29

StringBuilder **does not create a new string object** for each concatenation making it a **better use of memory** and more **performant**.

Question 30

Explain the concept of inner classes in Java

Answer 30

- Classes **defined within another class**. - They **have access to the members of the enclosing class** (including private members).

Question 31

When could you use an inner class in Java?

Answer 31

1. **Encapsulation**: Inner classes can encapsulate implementation details within the scope of the enclosing class. 2. **Implementing interfaces**: i.e. functional interfaces can be implemented using an anonymous inner class.