Java OOP Concepts and Methods
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Questions and Answers

Which relationship is represented by a class using another object, but without any ownership?

  • Aggregation
  • Dependence (correct)
  • Composition
  • Association

What kind of relationship is depicted in the example: A "Car" class has a "Engine" class, but the "Engine" can exist independently of the "Car"?

  • Composition
  • Aggregation (correct)
  • Dependence
  • Association

Which relationship suggests an "owns-a" connection between classes?

  • Inheritance
  • Composition (correct)
  • Association
  • Dependence

Which relationship type is indicated when one class simply utilizes methods from another class without maintaining ownership?

<p>Dependence (D)</p> Signup and view all the answers

Which of these relationships describes a "has-a" connection between classes, allowing the parts to exist independently?

<p>Association (C)</p> Signup and view all the answers

What is the purpose of the 'abs(x)' method in Java?

<p>To return the absolute value of x (B)</p> Signup and view all the answers

What is the primary function of Access Modifiers in Java?

<p>To control the access level of classes and methods (B)</p> Signup and view all the answers

Which of the following statements accurately describes the purpose of 'Composition' in Java?

<p>It defines a relationship where one object contains another object as a member. (B)</p> Signup and view all the answers

What is the difference between a 'class' and a 'method' in Java?

<p>A class defines the structure of an object, while a method defines actions an object can perform. (C)</p> Signup and view all the answers

What is the primary purpose of Java Modifiers?

<p>To restrict the accessibility of classes and methods (D)</p> Signup and view all the answers

What is the base case of the recursion method described in the algorithm?

<p>If n = 0 (B)</p> Signup and view all the answers

Which equation represents the recursive step of the algorithm?

<p>x^n = x * x^(n-1) (D)</p> Signup and view all the answers

What would be the result of the method if n is negative?

<p>The method will throw an error (C)</p> Signup and view all the answers

Why is this recursion method potentially less efficient than an iterative approach?

<p>It takes more memory due to stack calls (C)</p> Signup and view all the answers

What will the output of the recursion method be if x = 2 and n = 3?

<p>8 (C)</p> Signup and view all the answers

What does the problem space refer to in an Object Oriented Approach?

<p>The environment where the problem exists (A)</p> Signup and view all the answers

How does Object Oriented Programming (OOP) help in understanding problems?

<p>By allowing the problem to be described in its own terms (D)</p> Signup and view all the answers

What is the relationship between the problem space and the solution space in an Object Oriented Approach?

<p>The problem space defines the environment where the solution is applied. (B)</p> Signup and view all the answers

Which of the following statements is true regarding the problem and solution spaces?

<p>Understanding the problem space is essential for establishing a solution. (C)</p> Signup and view all the answers

What is the purpose of the Java String pool?

<p>To store all string literals to optimize memory usage (B)</p> Signup and view all the answers

Where are the strings in the Java String pool stored?

<p>In the heap memory (A)</p> Signup and view all the answers

Which of the following best characterizes the perspective of OOP towards problems?

<p>It translates real-world problems into computational formats. (D)</p> Signup and view all the answers

What happens when a new string is declared in Java?

<p>The JVM checks if the value exists in the String pool (A)</p> Signup and view all the answers

How does the JVM handle duplicate strings in the String pool?

<p>It merges duplicate strings into a single instance (B)</p> Signup and view all the answers

What is one advantage of using the String pool in Java?

<p>Reduces memory usage by eliminating duplicate strings (A)</p> Signup and view all the answers

What is a defining characteristic of a static variable in Java?

<p>It is shared among all instances of a class. (C)</p> Signup and view all the answers

Which of the following is a common use for static variables?

<p>Tracking the number of instances of a class. (A)</p> Signup and view all the answers

In which scenario would a static variable NOT be appropriate?

<p>When storing a unique identification number for each employee. (D)</p> Signup and view all the answers

How can a static variable in Java be accessed?

<p>Directly using the class name without an object reference. (C)</p> Signup and view all the answers

What is the primary benefit of using static variables in a class?

<p>They provide a way to maintain shared data among all instances. (C)</p> Signup and view all the answers

Flashcards

Problem Space

The place where the problem exists, like a business.

Solution Space

The place where you implement the solution, like a computer.

Association

The act of connecting the problem space with the solution space, finding a way to solve the problem within the computer.

Object-Oriented Programming (OOP)

An approach to programming that lets you describe a problem using the natural terms of that problem, instead of computer terms.

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OOP: Benefits for Problem Solving

OOP allows you to bridge the gap between the problem space and the solution space more easily, because it uses terms familiar to the problem itself.

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Recursion

A function that calls itself within its own definition.

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Recursive Function

A function that solves a problem by breaking it down into smaller, similar subproblems.

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Base Case

The base case in a recursive function is the stopping condition that prevents infinite recursion.

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Power Function

A recursive function that calculates the nth power of a number 'x' by repeatedly multiplying 'x' by itself 'n' times.

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Iterative Approach

An iterative approach to calculate the nth power of a number 'x' using a loop, which is typically more efficient than recursion.

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String in Java

A sequence of characters representing a text value. In Java, Strings are immutable, meaning their contents cannot be changed once created.

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Java String Pool

A special area in Java's heap memory where String objects are stored. When a new String object is created, the JVM checks if an identical String already exists in the pool. If it does, the existing String is reused. If not, a new String is created and added to the pool.

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String Pooling

The act of checking if a String already exists in the String Pool and reusing it if found.

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JVM's Role in String Pool

The Java Virtual Machine (JVM) is responsible for managing the String Pool, ensuring efficient use of heap memory by reusing existing String objects where possible.

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Creating Strings in Java

Strings created using the new keyword are always allocated new memory, even if an identical string already exists in the pool. Strings created using String literals (e.g., "Hello") are first checked for existence in the pool. If found, the existing String is reused.

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Access Modifiers

Modifiers that determine how accessible a class, method, or variable is from other parts of the program.

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Non-Access Modifiers

Modifiers that change the default behavior of a class, method, or variable. They specify special characteristics.

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Composition

A class that has a reference to an object of another class as its member.

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Class Relationship

A mechanism that allows you to create relationships between classes, like 'has-a' or 'uses-a' relationship.

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Access Level

They specify who can access your class, method, or variable (public, private, protected).

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Static variable (Java)

A variable that belongs to the class itself, rather than individual objects. It's shared across all objects of that class.

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Static (keyword)

A keyword in Java that indicates a variable is shared across all objects of a class. You access it using the class name, not an object.

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Class name access

A mechanism in Java that allows you to access a static variable or method without creating an object of that class.

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Non-static (instance) variable

Variables that are unique to each individual object of a class. Each object has its own copy of the variable.

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Common property

The name used to refer to a static variable. It's the same for all objects within the class.

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Dependence ("Uses-A")

One class uses methods or attributes from another class, but no direct ownership is established. Think of it as a temporary connection.

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Association ("Has-A")

One class owns an instance (object) of another class, forming a close, lasting connection.

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Inheritance ("Is-A")

One class inherits all features (methods and attributes) from another class, creating a parent-child relationship.

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Multiple Inheritance

A class can inherit properties from multiple parent classes.

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Single Inheritance

A class inherits properties from only one parent class.

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Study Notes

Object Oriented Programming (OOP) Course Notes

  • The course is titled "Object Oriented Programming" (OOP)
  • The course is taught at the Arab International University (AIU)
  • Recommended textbook: Java How to Program by Deitel & Deitel, 9th edition (6th+ editions also acceptable)

Lecture 1 Outline

  • History of OOP
  • Concept of Object Oriented Programming
  • Object Oriented Approach
  • Object & Classes
  • Some of OOP Languages
  • Java Language

History of OOP

  • Alan Kay is considered one of the fathers of OOP
  • The concept draws inspiration from biological cells

Concept of Object Oriented Programming

  • OOP is a programming paradigm that uses objects and their interactions to design applications
  • It's an approach to program organization and development

Object Oriented Approach

  • It involves establishing an association between problem space and solution space
  • Problem space: the area where the problem exists (e.g., a business)
  • Solution space: the area of implementation (e.g., a computer)

Object & Classes

  • OOP allows decomposition, creating objects and building attributes (data/variables) and methods (functions) around them
  • A class is a template from which many objects can be created
  • An object is an instance of a class
  • OOP programs create many different objects from templates known as Classes
  • Classes are types of objects

Some of OOP Languages

  • C++
  • Microsoft's Visual Basic
  • Java
  • C# (derived from C++ and Java, designed for integrating the internet and web into computer applications)

Java Language

  • Java is a popular object-oriented programming language
  • It's used for mobile apps (especially Android), desktop applications, web applications, and games, database connections, and much more
  • Java is platform-independent ("write once, run anywhere")
  • This is achieved by the Java Virtual Machine (JVM) translating source code to bytecodes to run on diverse computer systems and devices
  • Java programs use two compilation processes
  • Source code is translated into bytecodes
  • During execution, bytecodes are translated into machine language for the computing device

Lecture 2 Outline

  • Basic Structure of Java programs
  • Java Classes/Objects
  • Java Class Attributes
  • Java constructor
  • Java Packages
  • Java Data Types
  • Java Operators
  • Java I/O

Basic Structure of Java Programs

  • Every Java program consists of at least one class
  • Every line of code that runs in Java must be inside a class
  • The keyword class introduces a class declaration followed by the class name
  • The naming convention for Java files must match the class name followed by .java

Java Classes/Objects

  • To create a class in Java, use the keyword class
  • To create an object of a class, use the keyword new

Java Class Attributes (Variables)

  • Class attributes are variables within a class
  • Attributes can be accessed using objects and the dot syntax (.)
  • Attributes can be assigned/modified, and their values can be printed

Java Constructor

  • A constructor in Java is a special method used to initialize objects
  • The constructor name matches the class name
  • It does not have a return type
  • Constructors are called when an object is created

Java Packages

  • Packages group related classes
  • The Java API (Application Programming Interface) is a library of pre-written classes divided into packages and classes
  • Java uses the import keyword to access classes/packages from the library
  • Single classes or entire packages can be imported

Java Data Types

  • Primitive datatypes: byte, short, int, long, float, double, boolean, char
  • Non-primitive datatypes: String, arrays, classes

Java Operators

  • Arithmetic operators (+, -, *, /, %, ++, --) perform mathematical operations.
  • Assignment operators (=, +=, -=, *=, /=, %=) assign/modify values.
  • Comparison operators (==, !=, >, <, >=, <=) compare values.
  • Logical operators (&&, ||, !) perform logical operations.

Java I/O (Input/Output)

  • Java I/O is used for processing input and producing output
  • Java uses the concept of streams (sequences of data) to perform I/O operations

Lecture 3 Outline

  • Java Methods
  • Java Recursion
  • Java Strings
  • Java Math

Java Methods

  • A method is a block of code that runs when called
  • Methods can take parameters (data)
  • They can also perform actions and are sometimes called functions.
  • Methods are declared within a class
  • To reuse code define it once, and then reuse it multiple times
  • Java has some pre-defined methods (e.g., println)

Java Recursion

  • Recursion is a method calling itself
  • Used to break complex problems into smaller simpler ones
  • The method should have a stopping condition (to avoid infinite recursion); in the example given, it is where the parameter k becomes 0

Java Strings

  • Strings are used to store text
  • Strings are objects of type String
  • Strings can be created using literals or the 'new' keyword
  • String objects are immutable (cannot be changed) after creation

Java Math

  • The Math class provides methods for mathematical tasks on numbers (e.g., max, min, sqrt, abs)

Subsequent Lectures (4-6)

  • Topics discussed include Java Modifiers, Composition, Java Strings, details on the String class and its methods (concat, equals, length, charAt, etc.) , memory allocation of String, and Java Math functions.

Lecture 7-9

  • Focuses on Inheritance, Polymorphism, Conclusion, and Review

  • Also covers Java Files: creating, reading, writing, and deleting files, showing the use of File, PrintWriter, FileReader, and Scanner.

  • This lecture covers Java Exceptions (try...catch) mechanisms to deal with errors during program execution.

  • Additional data on the use of super, toString, and equals in Java programming are also given.

  • Notes on multiple inheritance also cover topics that include usage of super, in relation to methods from the parent class's (grandparent-class)

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Java Programming Introduction PDF

Description

Test your knowledge of object-oriented programming concepts in Java, focusing on class relationships such as composition and associations, as well as Java methods and modifiers. The quiz covers fundamental principles and specific Java functions to enhance your understanding of programming structures.

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