Java Fundamentals (D286)

Java Fundamentals (D286) Study Notes

Table of Contents

1. Introduction to Java

   • What is Java?
   • Features of Java
   • Java Development Kit (JDK) and Java Runtime Environment (JRE)
   • Writing Your First Java Program
2. Java Syntax and Data Types
   • Variables and Data Types
   • Operators
   • Control Flow Statements (if-else, loops, switch)
3. Object-Oriented Programming (OOP) in Java
   • Classes and Objects
   • Inheritance, Polymorphism, Encapsulation, and Abstraction
   • Constructors and Methods
4. Arrays and Strings
   • Working with Arrays
   • String Manipulation
5. Exception Handling
   • Types of Exceptions
   • Try-Catch Blocks
   • Custom Exceptions
6. File Handling in Java
   • Reading and Writing Files
   • File Class Methods
7. Case Study 1: Building a Student Management System
   • Problem Statement
   • Solution Design
   • Code Implementation
   • Analysis
8. Case Study 2: Creating a Banking Application
   • Problem Statement
   • Solution Design
   • Code Implementation
   • Analysis
9. Practice Questions and Answers
   • 100 Q&A with Rationales

1. Introduction to Java

Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle). It is platform-independent, meaning Java programs can run on any device with a Java Virtual Machine (JVM).

• Platform Independence: Write once, run anywhere (WORA).
• Object-Oriented: Everything in Java is an object.
• Secure: Built-in security features like bytecode verification.
• Multithreading: Supports concurrent execution of multiple threads.

• JDK: Used to develop Java applications. Includes tools like javac (compiler) and java (interpreter).
• JRE: Provides the runtime environment to execute Java programs.

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public class HelloWorld {

    public static void main(String[] args) {

        System.out.println("Hello, World!");

    }

}

• Explanation:
  • public class HelloWorld: Defines a class named HelloWorld.
  • public static void main(String[] args): The main method where execution begins.
  • System.out.println("Hello, World!");: Prints "Hello, World!" to the console.

Introduction to Java programming.

2. Java Syntax and Data Types

• Primitive Data Types: int, double, char, boolean, etc.
• Reference Data Types: Objects, arrays, and strings.

Example:

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int age = 25;

double salary = 50000.50;

char grade = 'A';

boolean isJavaFun = true;

• Arithmetic Operators: +, -, *, /, %
• Comparison Operators: ==, !=, >, <
• Logical Operators: &&, ||, !

Example:

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int a = 10, b = 20;

if (a > b) {

    System.out.println("a is greater");

} else {

    System.out.println("b is greater");

}

• If-Else:

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int marks = 85;

if (marks >= 90) {

    System.out.println("Grade A");

} else if (marks >= 80) {

    System.out.println("Grade B");

} else {

    System.out.println("Grade C");

}

• Loops:

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for (int i = 1; i <= 5; i++) {

    System.out.println("Iteration: " + i);

}

Object-Oriented Programming (OOP) in Java

• Class: A blueprint for creating objects.
• Object: An instance of a class.

Example:

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class Car {

    String color;

    int speed;

    void accelerate() {

        speed += 10;

    }

}

Car myCar = new Car();

myCar.color = "Red";

myCar.accelerate();

• Allows a class to inherit properties and methods from another class.

Example:

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class Vehicle {

    void run() {

        System.out.println("Vehicle is running");

    }

}

class Bike extends Vehicle {

    void accelerate() {

        System.out.println("Bike is accelerating");

    }

}

• The ability of a method to perform different tasks.

Example:

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class Animal {

    void sound() {

        System.out.println("Animal makes a sound");

    }

}

class Dog extends Animal {

    void sound() {

        System.out.println("Dog barks");

    }

}

Java Power Tools: Model software for teaching object-oriented design.

4. Arrays and Strings

• Arrays store multiple values of the same type.

Example:

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int[] numbers = {1, 2, 3, 4, 5};

for (int num : numbers) {

    System.out.println(num);

}

• Strings are immutable in Java.

Example:

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String name = "Java";

System.out.println(name.length()); // Output: 4

System.out.println(name.toUpperCase()); // Output: JAVA

Strings and Arrays.

5. Exception Handling

• Checked Exceptions: Compile-time exceptions (e.g., IOException).
• Unchecked Exceptions: Runtime exceptions (e.g., NullPointerException).

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try {

    int result = 10 / 0;

} catch (ArithmeticException e) {

    System.out.println("Cannot divide by zero");

}

Exception handling: A field study in java and. net.

6. File Handling in Java

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import java.io.File;

import java.io.FileWriter;

import java.io.IOException;

public class FileExample {

    public static void main(String[] args) {

        try {

            FileWriter writer = new FileWriter("example.txt");

            writer.write("Hello, Java!");

            writer.close();

        } catch (IOException e) {

            System.out.println("An error occurred.");

        }

    }

7. Case Study 1: Building a Student Management System

Create a program to manage student records, including adding, updating, and displaying student details.

• Use classes to represent students.
• Use arrays or collections to store student data.

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class Student {

    String name;

    int rollNo;

    double marks;

    Student(String name, int rollNo, double marks) {

        this.name = name;

        this.rollNo = rollNo;

        this.marks = marks;

    }

    void display() {

        System.out.println("Name: " + name + ", Roll No: " + rollNo + ", Marks: " + marks);

    }

}

public class StudentManagement {

    public static void main(String[] args) {

        Student[] students = new Student[3];

        students[0] = new Student("Alice", 1, 95.5);

        students[1] = new Student("Bob", 2, 88.0);

        students[2] = new Student("Charlie", 3, 91.0);

        for (Student s : students) {

            s.display();

        }

    }

}

• The program uses OOP principles to manage student data.
• Arrays store multiple student objects, and a loop displays their details.

8. Case Study 2: Creating a Banking Application

Develop a simple banking application to deposit, withdraw, and check balance.

• Use a class to represent a bank account.
• Implement methods for deposit, withdrawal, and balance inquiry.

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class BankAccount {

    double balance;

    BankAccount(double initialBalance) {

        this.balance = initialBalance;

    }

    void deposit(double amount) {

        balance += amount;

        System.out.println("Deposited: " + amount);

    }

    void withdraw(double amount) {

        if (amount > balance) {

            System.out.println("Insufficient balance");

        } else {

            balance -= amount;

            System.out.println("Withdrawn: " + amount);

        }

    }

    void checkBalance() {

        System.out.println("Balance: " + balance);

    }

}

public class BankingApp {

    public static void main(String[] args) {

        BankAccount account = new BankAccount(1000);

        account.deposit(500);

        account.withdraw(200);

        account.checkBalance();

    }

}

• The program demonstrates encapsulation by keeping the balance private and providing methods to interact with it.
• It handles edge cases like insufficient balance during withdrawals.

Q&A Section

Question 1:

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public class Main {

    public static void main(String[] args) {

        int x = 5;

        int y = x++;

        System.out.println(y);

    }

}

Options:
A) 5
B) 6
C) 0
D) Compilation Error

Explanation of Correct Answer:

• The x++ operator is a post-increment operator. This means the value of x is first assigned to y, and then x is incremented by 1.
• In this code:
  • x is initially 5.
  • y = x++ assigns the current value of x (which is 5) to y.
  • After the assignment, x is incremented to 6, but y remains 5.
• Therefore, the output of System.out.println(y) is 5.

B) 6: This would be correct if the code used the pre-increment operator (++x). However, x++ increments x after the assignment, so y is not affected by the increment.

C) 0: There is no logical or syntactical reason for y to be 0. This option is incorrect.

D) Compilation Error: The code is syntactically correct and will compile without errors. This option is incorrect.

Question 2:

Options:
A) Platform Independence
B) Object-Oriented
C) Pointers
D) Multithreading

Correct Answer: C) Pointers

Explanation of Correct Answer:

• Java does not support pointers explicitly. Pointers are a feature of languages like C and C++, which allow direct memory manipulation. Java avoids pointers to ensure security and simplicity.
• Instead of pointers, Java uses references to interact with objects, which are safer and managed by the JVM.

A) Platform Independence: This is a core feature of Java. Java programs are compiled into bytecode, which can run on any device with a JVM, making it platform-independent.

B) Object-Oriented: Java is fundamentally object-oriented, meaning everything in Java is an object (except primitive data types).

D) Multithreading: Java supports multithreading, allowing concurrent execution of multiple threads within a program.

Question 3:

Options:
A) To create a constant variable
B) To allow a method or variable to belong to the class rather than an instance
C) To prevent a class from being instantiated
D) To make a variable thread-safe

Explanation of Correct Answer:

• The static keyword is used to define class-level methods and variables. These belong to the class itself rather than any specific instance of the class.
• For example:
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class Counter {

    static int count = 0; // Class-level variable

    Counter() {

        count++;

    }

• }

Here, count is shared across all instances of the Counter class.

A) To create a constant variable: Constants are created using the final keyword, not static. For example: final int MAX_VALUE = 100;.

C) To prevent a class from being instantiated: This is achieved by making the class abstract or defining a private constructor, not by using static.

D) To make a variable thread-safe: The static keyword does not inherently make a variable thread-safe. Thread safety is achieved using synchronization or other concurrency mechanisms.

Question 4:

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public class Main {

    public static void main(String[] args) {

        String str1 = "Java";

        String str2 = new String("Java");

        System.out.println(str1 == str2);

    }

}

Options:
A) true
B) false
C) Compilation Error
D) Runtime Error

Explanation of Correct Answer:

• In Java, the == operator checks for reference equality, not content equality.
• str1 is a string literal stored in the string pool, while str2 is a new object created in the heap memory.
• Even though both strings contain the same content ("Java"), they refer to different memory locations. Therefore, str1 == str2 evaluates to false.

A) true: This would be correct if the code used the .equals() method, which checks for content equality. For example: str1.equals(str2) would return true.

C) Compilation Error: The code is syntactically correct and will compile without errors.

D) Runtime Error: There is no runtime error in this code. It will execute and produce the output false.

Question 5:

Options:
A) Checked exceptions are checked at runtime.
B) Unchecked exceptions are checked at compile time.
C) Checked exceptions must be handled using try-catch or declared in the method signature.
D) Unchecked exceptions are always fatal and cannot be handled.

Explanation of Correct Answer:

• Checked exceptions are exceptions that are checked at compile time. Examples include IOException and SQLException.
• Java requires that checked exceptions either be:
  • Caught using a try-catch block, or
  • Declared in the method signature using the throws keyword.

A) Checked exceptions are checked at runtime: This is incorrect. Checked exceptions are checked at compile time, not runtime.

B) Unchecked exceptions are checked at compile time: This is incorrect. Unchecked exceptions (e.g., NullPointerException, ArithmeticException) are not checked at compile time. They occur at runtime.

D) Unchecked exceptions are always fatal and cannot be handled: This is incorrect. Unchecked exceptions can be handled using try-catch blocks, but they are not required to be handled.

Question 6:

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public class Main {

    public static void main(String[] args) {

        int[] numbers = {1, 2, 3, 4, 5};

        System.out.println(numbers[5]);

    }

}

Options:
A) 5
B) 0
C) ArrayIndexOutOfBoundsException
D) Compilation Error

Explanation of Correct Answer:

• Arrays in Java are zero-indexed, meaning the first element is at index 0.
• The array numbers have 5 elements, so the valid indices are 0 to 4.
• Accessing numbers[5] tries to access the 6th element, which does not exist. This results in an ArrayIndexOutOfBoundsException.

A) 5: This would be correct if the code accessed numbers[4], which is the last element of the array.

B) 0: There is no logical reason for the output to be 0. This option is incorrect.

D) Compilation Error: The code is syntactically correct and will compile without errors. The error occurs at runtime.