Java Fundamentals: Arrays, Loops, Classes, and Methods

Posted on Jan 7, 2025 in Other university degrees and diplomas

Java Arrays

In Java, arrays are a fundamental data structure used to store collections of elements of the same type. Here’s how you can declare and initialize a String array:

String[] cars = {"BMW", "Ford", "Mazda"};

You can determine the length of an array using the .length property:

System.out.println(cars.length);

Iterate through an array using a for loop:

for (int i = 0; i < cars.length; i++) {

Multidimensional Arrays in Java

Java supports multidimensional arrays, which are essentially arrays of arrays. Here’s an example of a two-dimensional integer array:

int[][] myNumbers = {{1, 2, 3, 4}, {5, 6, 7}};

You can iterate through a multidimensional array using nested for loops:

for (int i = 0; i < myNumbers.length; i++) {

    for (int j = 0; j < myNumbers[i].length; j++) {

        System.out.println(myNumbers[i][j]);

    }

}

Java Class Example: Speeding Ticket

Here’s an example of a Java class representing a speeding ticket:

SpeedingTicket sp1 = new SpeedingTicket(1234, 40, 20191010, 30);

System.out.println(sp1.getTicketNumber());

System.out.println(sp1.getActualSpeed());

System.out.println(sp1.getDate());

System.out.println(sp1.getSpeedLimit());

System.out.println(sp1.getOverage());

System.out.println(sp1.getFileNumber());

Switch Statements in Java

Switch statements provide a way to execute different code blocks based on the value of an expression:

switch (theMovieName) {

    case "Batman":

        message = "Batman is at 7:30 PM";

        break;

}

Static vs. Instance Variables

Static Variables: Static variables are associated with the class itself rather than with instances of the class. Their value is the same across all instances.

Instance Variables: Instance variables are specific to each instance of a class.

Java Class Example: Movie Ticket

Here’s an example of a Java class for a movie ticket reservation system:

MovieTicket ticket = new MovieTicket();

System.out.println("Please enter your movie name: ");

ticket.setMovieName(in.nextLine());

System.out.println("Please enter ticket number: ");

ticket.setTicketNumber(in.nextInt());

System.out.println("Please enter your theater number: ");

ticket.setTheatreNumber(in.nextInt());

System.out.println("Ticket price is: " + MovieTicket.taxTotal());

ticket.setTicketPrice(in.nextInt());

String Manipulation in Java

• firstName.toUpperCase(): Converts the string to uppercase.
• .length: Returns the length of the string.
• .charAt(3): Returns the character at index 3.
• .substring(0, 3): Returns a substring from index 0 up to 3.
• .indexOf("a"): Returns the index of the first occurrence of “a”.

Constants in Java

public static Double Tax = 1.13;

public static final Double TAX = 3;

Array Declarations

Multidimensional Array

int[][] A = {

    {1, 2, 3},

    {1, 2, 3},

    {4, 5, 6}

};

Single-Dimensional Array

int[] c = new int[12];

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

Java Class: Airline Reservation

This class represents an airline reservation with a first name, last name, flight number, and seat number.

/**
 * This class will give a first name, last name, a flight number, and a seat number.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class AirlineReservation {
    private String firstName;
    private String lastName;
    private int flightNumber;
    private int seatNumber;
    private String message;

    public AirlineReservation() {
    }

    public AirlineReservation(String firstName, String lastName, int flightNumber, int seatNumber) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.flightNumber = flightNumber;
        this.seatNumber = seatNumber;
        this.message = message;
    }

    // Setter methods
    public void setFirstName(String setFirstName) {
        firstName = setFirstName;
    }

    public void setLastName(String setTheLastName) {
        lastName = setTheLastName;
    }

    public void setFlightNumber(int setFlightNumber) {
        flightNumber = setFlightNumber;
    }

    public void setSeatNumber(int setSeatNumber) {
        seatNumber = setSeatNumber;
    }

    public void setMessage(String setMessage) {
        message = setMessage;
    }

    // Getter methods
    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public int getFlightNumber() {
        return flightNumber;
    }

    public int getSeatNumber() {
        return seatNumber;
    }

    public String getMessage() {
        return message;
    }

    public String getSeatClass() {
        switch (seatNumber) {
            case 1:
            case 2:
            case 3:
                message = "First Class";
                break;
            case 4:
            case 5:
            case 6:
                message = "Second Class";
                break;
            case 7:
            case 8:
            case 9:
                message = "Third Class";
                break;
            case 10:
            case 11:
            case 12:
                message = "Fourth Class";
                break;
        }
        return message;
    }

    public String upperCaseName() {
        for (int i = 0; i < firstName.length(); i++) {
            System.out.println(firstName.toUpperCase().charAt(i));
        }
        return firstName.toUpperCase();
    }
}