Java Classes and Objects Study List

Question 1

Describe inheritance

Answer 1

Inheritance is a fundamental concept in object-oriented programming (OOP) that allows a class to inherit properties and behaviours from another class. It enables code reuse and the creation of hierarchical relationships between classes.

The subclass can access and extend the members (fields and methods) of the superclass.

Question 2

Describe polymorphism

Answer 2

Polymorphism refers to the ability of an object to take on many forms. In Java, polymorphism allows objects of different classes to be treated as objects of a common superclass. It enables code to work with objects in a more general way, increasing flexibility and modularity. Polymorphism is achieved through method overriding and method overloading.

Subclasses can be treated as if they are superclasses.

Question 3

Describe encapsulation

Answer 3

Encapsulation is a principle of OOP that combines data and methods into a single unit called a class. It promotes the idea of hiding internal implementation details and providing a public interface to interact with the class. Encapsulation helps in achieving data protection, abstraction, and code maintainability by preventing direct access to data and enforcing access through methods (getters and setters).

Question 4

Describe abstraction

Answer 4

Define the essential characteristics of an object while hiding the implementation details.

Abstraction can be achieved through abstract classes and interfaces in Java.

Question 5

Describe the single responsibility principle

Answer 5

The Single Responsibility Principle (SRP) states that a class should have only one reason to change. It suggests that a class should have a single responsibility or purpose and should encapsulate only one aspect of functionality. By adhering to SRP, classes become more focused, maintainable, and reusable. It promotes better code organization and separation of concerns.

Question 6

What is a class?

Answer 6

A class is a blueprint or template that defines the structure, behavior, and initial state of objects. It serves as a blueprint for creating multiple instances of objects.

Question 7

What is an object?

Answer 7

An object is a specific instance of a class. It represents a real-world entity and has its own unique state and behaviour.

Question 8

What is an accessor/getter?

Answer 8

An accessor or getter is a method in a class that provides access to the value of a private or protected instance variable. It allows other classes to retrieve the value of the variable without directly accessing it. Getters typically follow the naming convention getVariableName(), where “VariableName” is the name of the variable being accessed.

Question 9

What is a mutator/setter?

Answer 9

A mutator or setter is a method in a class that allows the modification or assignment of a value to a private or protected instance variable. It provides a way to update the value of a variable while encapsulating the logic or constraints associated with the assignment. Setters typically follow the naming convention setVariableName(), where “VariableName” is the name of the variable being modified.

Question 10

What is a constructor?

Answer 10

A constructor is a special method in a class that is used to initialize the object of that class. It is called automatically when an object is created using the “new” keyword. Constructors have the same name as the class and can have parameters to accept initial values for the object’s instance variables. Constructors are used to set up the initial state of an object.

Question 11

What is shadowing? (not best practice).

Answer 11

Shadowing occurs when a variable in a nested scope (such as a method or block) has the same name as a variable in the enclosing scope. It leads to the overshadowing or hiding of the variable in the outer scope, making it inaccessible within the inner scope. Shadowing can cause confusion and should be avoided for better code readability.

Question 12

What is a static method

Question 13

What is scope of public access modifier

Answer 13

Public: Accessible from anywhere, both within and outside the class.

Question 14

What is scope of private access modifier

Answer 14

Private: Accessible only within the same class. Not visible to other classes.

Question 15

What is the scope of a class without an access modifier

Answer 15

Default (no explicit modifier): Accessible within the same package but not outside the package.

Question 16

What is scope of protected access modifier

Answer 16

Protected: Accessible within the same class, subclasses, and other classes in the same package.

Question 17

What is a static object

Answer 17

In Java, the terms “static object” and “non-static object” are not commonly used. However, we can discuss static members and non-static members within a class.

Question 18

What is a static method

Answer 18

Static methods and variables belong to the class itself rather than individual instances of the class. They can be accessed without creating an object of the class.

Question 19

What is a non-static method

Answer 19

Non-static methods and variables are associated with specific instances (objects) of the class and require an object to be accessed.

Question 20

What does the abstract keyword mean?

Answer 20

The abstract keyword is used to declare abstract classes and methods in Java. An abstract class cannot be instantiated and serves as a blueprint for creating concrete subclasses.

Question 21

How is the abstract keyword used in conjunction with classes?

Answer 21

Abstract methods are declared without a body and must be implemented in the subclasses. Abstract classes provide common behavior and attributes that can be inherited by multiple subclasses.

Question 22

How is the collection class used?

Answer 22

The Collection class is a built-in class in Java that provides a framework for working with groups of objects. It is a high-level interface that defines common methods and behaviors for collections. Collection classes, such as ArrayList, HashSet, and HashMap, implement the Collection interface and provide specific implementations for storing and manipulating groups of objects.

Question 23

What does it mean if a class is cohesive?

Answer 23

A cohesive class is a class that has a single, well-defined responsibility or purpose. It focuses on a specific area of functionality and encapsulates related data and methods. A cohesive class is highly focused and avoids unnecessary dependencies on other classes or responsibilities.

Question 24

What is a local class?

Answer 24

A local class is a class defined within a block, such as a method or a constructor, within another class. It is only accessible within the block where it is defined and is often used for implementing callbacks or specific functionality within a limited scope.

Question 25

What level of access to the properties and methods of the enclosing class does a static nested class have?

Answer 25

A static nested class has access to the public and protected properties and methods of the enclosing class.

Question 26

Under what conditions can a local class access variables in the enclosing scope?

Answer 26

A local class can access variables in the enclosing scope if they are effectively final or declared as final.

Question 27

Write a constructor for a Car class that takes action and reaction parameters.

Answer 27

public class Car { private String action; private String reaction; public Car(String action, String reaction) { this.action = action; this.reaction = reaction; } }

Question 28

Write the getters and setters for your Dog class.

Answer 28

public class Dog { private String name; private int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }

Question 29

Give an example of an interface.

Answer 29

public interface Drawable { void draw(); }

Question 30

Write an interface for airplane operations (turn left, climb, and so on). Create a class called AirBus787 that implements your interface.

Answer 30

public interface AirplaneOperations { void turnLeft(); void turnRight(); void climb(); void descend(); }

Question 31

Can you instantiate an interface?

Answer 31

Instantiating an Interface directly is not possible in Java. Interfaces are meant to be implemented by classes.

Question 32

Compare and contrast the keywords extends and implements.

Answer 32

"Extends" is used to establish an inheritance relationship between classes. It allows a subclass to inherit the properties and behaviors of a superclass. "Implements" is used to indicate that a class is implementing one or more interfaces. It defines the contract that the class must adhere to by implementing the methods specified in the interface.

Question 33

When do you use the extends keyword

Answer 33

"Extends" is used to establish an inheritance relationship between classes. It allows a subclass to inherit the properties and behaviours of a superclass.

Question 34

When do you use the implements keyword?

Answer 34

"Implements" is used to indicate that a class is implementing one or more interfaces. It defines the contract that the class must adhere to by implementing the methods specified in the interface.

Question 35

If you have no access modifiers what is the default on your class?

Answer 35

If no access modifier is specified for a class, it has the default access level, which means it can be accessed within the same package but not from outside the package.

Question 36

What is the base class of all classes?

Answer 36

The base class of all classes in Java is the Object class. All other classes in Java are either directly or indirectly derived from the Object class.

Question 37

What is a List?

Answer 37

List is an interface that represents an ordered collection of elements. It allows duplicate elements and provides methods for accessing, modifying, and iterating over the elements.

Question 38

What is an ArrayList?

Answer 38

ArrayList is a class that implements the List interface. It provides a dynamic array implementation of the List interface, allowing elements to be added, removed, and accessed by their index. ArrayList automatically adjusts its size as elements are added or removed.

Question 39

What is a Set?

Answer 39

Set is an interface that represents a collection of unique elements with no defined ordering. It does not allow duplicate elements.

Question 40

What is a HashSet?

Answer 40

HashSet is a class that implements the Set interface. It uses a hash table data structure to store elements, providing constant-time performance for basic operations like add, remove, and contains. HashSet does not guarantee the order of elements.

Question 41

What is a Map?

Answer 41

Map is an interface that represents a mapping between keys and values. Each key in a Map is associated with a unique value, and keys are unique within a Map.

Question 42

What is a HashMap?

Answer 42

HashMap is a class that implements the Map interface. It uses a hash table data structure to store key-value pairs, providing fast retrieval and insertion of elements. HashMap does not guarantee the order of keys or values.

Question 43

What is the difference between derived and extended classes?

Answer 43

There is no specific distinction between "derived" and "extended" classes in Java. Both terms generally refer to classes that inherit from another class, either directly or indirectly.

Question 44

How does inheritance help achieve polymorphism?

Answer 44

Inheritance allows subclasses to inherit properties and behaviors from their superclass. This enables polymorphism, which means that objects of different classes can be treated as objects of a common superclass. Polymorphism allows for more flexibility in designing and using classes, as it allows objects to be used interchangeably based on their shared superclass behavior.

Question 45

What is an abstract base class?

Answer 45

An abstract base class is a class that is declared with the abstract keyword and cannot be instantiated. It is designed to be subclassed and serves as a common base for derived classes. Abstract base classes can define abstract methods (methods without implementation) that must be implemented by concrete subclasses.

Question 46

What is a superclass?

Answer 46

A superclass is a class that is higher in the inheritance hierarchy and from which other classes (subclasses) are derived. The superclass provides common attributes and behaviors that are inherited by its subclasses. Subclasses can add additional features or override inherited methods.

Question 47

What is a subclass?

Answer 47

A subclass is a class that is derived from a superclass. It inherits the properties and behaviors of the superclass and can extend or modify them as needed. Subclasses can add new attributes and methods, override inherited methods, or introduce new methods.

Question 48

How do you read from a file?

Answer 48

import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; public class FileReaderExample { public static void main(String[] args) { try (BufferedReader reader = new BufferedReader(new FileReader("file.txt"))) { String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } catch (IOException e) { e.printStackTrace(); } } }

Question 49

How do you write to a file?

Answer 49

import java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; public class FileWriterExample { public static void main(String[] args) { try (BufferedWriter writer = new BufferedWriter(new FileWriter("file.txt"))) { writer.write("Hello, World!"); writer.newLine(); writer.write("This is a sample file."); } catch (IOException e) { e.printStackTrace(); } } }

Question 50

What does it mean to be loosely coupled?

Answer 50

Loosely coupled refers to a design principle where components or modules in a system have minimal dependencies on each other. It promotes flexibility, modularity, and easier maintenance. Loosely coupled components can be modified, replaced, or tested independently without affecting other parts of the system.

Question 51

Why is it a good idea to split your applications into layers?

Answer 51

Splitting applications into layers is a common architectural approach that separates different concerns and responsibilities. Each layer has a specific purpose and interacts with adjacent layers through well-defined interfaces. This promotes modular design, code reusability, and easier maintenance.

Question 52

How do you use MVC as a design pattern in Java?

Answer 52

MVC (Model-View-Controller) is a design pattern that separates the application into three main components: Model: Represents the data and business logic of the application. View: Displays the user interface and interacts with the user. Controller: Handles user input, updates the model, and manages the flow of data between the model and view. MVC helps in achieving separation of concerns, promoting code organization, maintainability, and reusability.

Question 53

Categorize the following file into its MVC groups: Supplier class

Answer 53

Supplier class: Model

Question 54

Categorize the following file into its MVC groups: Game class

Answer 54

Game class: Model or Controller

Question 55

Categorize the following file into its MVC groups: Class that maps URLs to actions

Answer 55

Class that maps URLs to actions: Controller

Question 56

Categorize the following file into its MVC groups: List of actions you can do with the data

Answer 56

List of actions you can do with the data: Model

Question 57

Categorize the following file into its MVC groups: Implementation of those actions you use in your app

Answer 57

Controller

Question 58

Categorize the following file into its MVC groups: Data you use inside of your app

Answer 58

Model

Question 59

Categorize the following file into its MVC groups: Business rules of your app

Answer 59

Model or Controller

Question 60

What is a Waterfall SDLC methodology?

Answer 60

A traditional sequential software development methodology where each phase (requirements, design, implementation, testing, deployment) is completed before moving to the next. It follows a top-down approach with minimal customer involvement and minimal flexibility for changes once a phase is completed.

Question 61

What does SDLC stand for?

Answer 61

Software Development Life Cycle

Question 62

What is the Agile SDLC methodology?

Answer 62

An iterative and incremental software development methodology that focuses on collaboration, adaptability, and customer involvement. It emphasizes frequent delivery of working software, continuous feedback, and flexibility to accommodate changes throughout the development process.

Question 63

What is a checked exception?

Answer 63

Checked exceptions are always subject to the "catch or specify" requirement. Checked exceptions are exceptions that the compiler requires to be explicitly caught or declared in the method signature using the throws keyword. They typically represent recoverable conditions that a program can anticipate and handle.

Question 64

What is an unchecked exception?

Answer 64

Unchecked exceptions, also known as runtime exceptions, do not require explicit handling or declaration. They are usually caused by programming errors or unexpected conditions and represent unrecoverable situations. Unchecked exceptions can be caught and handled, but it is not mandatory.

Question 65

Explain how a try/catch/finally block of code works.

Answer 65

The try/catch/finally block is used to handle exceptions in Java. The try block contains the code that may throw an exception. The catch block catches and handles the exception, allowing the program to recover or take appropriate action. The finally block, if present, is executed regardless of whether an exception occurs or is caught. It is typically used to release resources or perform cleanup operations.

Question 66

When would you need to use the throws keyword?

Answer 66

The throws keyword is used in the method signature to indicate that a method may throw one or more exceptions. It specifies that the method is not handling the exceptions itself but will pass them to its caller to handle. The caller of the method must either catch the exception or declare it in its own method signature using the throws keyword.

Question 67

What are static members?

Answer 67

static members are associated with the class itself and can be accessed without creating an instance of the class

Question 68

What are non-static members?

Answer 68

non-static members belong to individual instances of the class and require an instance to be accessed.

Question 69

Code to access a static member

Answer 69

To access a static member, you can use the class name followed by the member name, like MyClass.staticVariable or MyClass.staticMethod().

Question 70

Code to access non-static member

Answer 70

To access a non-static member, you need to create an instance of the class and use that instance to access the member, like MyClass myObject = new MyClass(); myObject.nonStaticVariable or myObject.nonStaticMethod().

Question 71

What does static mean

Answer 71

1 per class

Question 72

What are collections

Answer 72

In Java, collections refer to objects that are used to store, manipulate, and organize groups of elements. They provide a way to efficiently manage and operate on groups of related objects. Some commonly used collection interfaces in Java include List, Set, Queue, and Map.

Question 73

What are collection interfaces in Java?

Answer 73

List, Set, Queue, and Map.

Question 74

What are examples of implementations of the collection interfaces?

Answer 74

ArrayList, HashSet, LinkedList, and HashMap

Question 75

What are primitive types?

Answer 75

There are eight primitive types in Java: byte: 8-bit integer value. short: 16-bit integer value. int: 32-bit integer value. long: 64-bit integer value. float: single-precision 32-bit floating-point value. double: double-precision 64-bit floating-point value. boolean: true or false char: Represents a single Unicode character.

Question 76

What functionalities do Collections offer?

Answer 76

Adding, removing, searching, sorting, and iterating over elements. They can hold objects of any type, including primitives (through wrapper classes), and can dynamically resize to accommodate the number of elements.

Question 77

Is String a Primitive type?

Answer 77

No. String is a class that represents a sequence of characters.

Question 78

What is the Java Collections Framework?

Answer 78

provides a set of interfaces and classes that define various types of collections and their associated operations.

Question 79

What is a wrapper class?

Answer 79

it allows a primitive type to be used as an object in Java. A class that wraps or encapsulates a primitive type and provides additional methods and functionality to work with that primitive type as an object.

Question 80

What is a functional interface?

Answer 80

A functional interface in Java is an interface that has exactly one abstract method. It serves as the foundation for lambda expressions and functional programming in Java.

Question 81

What are generics

Answer 81

Generics in Java are a way to create classes, interfaces, and methods that can work with different data types while maintaining type safety. They allow you to define classes and methods that are parameterized by one or more types. Cannot use primitive type, need to use wrapper class instead

Question 82

What is the syntax for generics?

Answer 82

ArrayList people = new ArrayList();

Question 83

What are Collections?

Answer 83

Collections are data structures that allow us to store multiple values with more flexibility than simple arrays provide.

Question 84

List some examples of collections

Answer 84

Collections usually represent a group of related data such as a class of students, a group of addresses, or a list of classes in a school schedule.

Question 85

What is an interface?

Answer 85

A contract. A Java interface is a list of methods that must be implemented by any class that claims to fulfill that interface

Question 86

What are the 5 exception handling keywords?

Answer 86

Throw, throws, try, catch, finally

Question 87

Why handle exceptions?

Answer 87

predictable error conditions are expected and do not crash the program because additional code is written to handle these run-time errors.

Question 88

What is an exception?

Answer 88

An exceptional event which occurs in the normal execution of a program that disrupts the normal flow of the program's instructions.

Question 89

What 2 categories of exceptions are there?

Answer 89

Checked and unchecked

Question 90

What are the 2 types of unchecked exceptions?

Answer 90

Errors and runtime exceptions

Question 91

What is method overloading?

Answer 91

when two methods share the same name but different parameter lists.

Question 92

How do you declare a java Interface?

Answer 92

With the interface keyword

Question 93

What are the benefits of inheritance?

Answer 93

Inheritance allows for more maintainable code because it cuts down on repeated code. Inheritance allows child classes to reuse code written in parent classes.

Question 94

All interface variables are _______ by default in Java.

Answer 94

public, static, final

Question 95

A static method of an interface should be accessed with ______ and a dot operator?

Answer 95

the interface name

Question 96

What is composition?

Answer 96

Composition refers the fact that objects can be made up of other objects.

Question 97

What must you do when implementing a Java interface?

Answer 97

Provide implementations for all methods declared in the interface or mark the class as abstract.

Question 98

What does the 'new' keyword do?

Answer 98

When you use the new keyword followed by a class name and parentheses, Java allocates memory to create a new object of that class. Person person = new Person();

Question 99

What is the key concept of Agile Development?

Answer 99

Build the simplest thing that could possibly work

Question 100

What are the phases of OpenUP SDLC?

Answer 100

Inception, Elaboration, Construction and Transition

Question 101

Which question is under the Elaboration phase of OpenUP SDLC?

Answer 101

Do we find that the value delivered so far and the remaining risk is acceptable?

Question 102

Which question is under the Construction phase of OpenUP SDLC?

Answer 102

Are we close to release? (This answer is unverified)

Question 103

What are quality strategies of Agile?

Answer 103

Continuous improvement, continuous reviews Short, fixed-length feedback cycles Dynamic code analysis The project goals are defined and adaptable.

Question 104

What level of focus is reserved for Iteration lifecycle?

Answer 104

Team focus

Question 105

What are disadvantages of the Agile model?

Answer 105

There is not always a clear vision of a "final project." New requirements may conflict with the existing architecture. Documentation is limited because it is usually "just in time."

Question 106

SDLC Context: What is expected within a single monthly iteration?

Answer 106

Stable weekly build