Constructor + Instance
- Constructor is used to create the instance of the class
- Instance: object created in the class
Java Hello
// class definition
class Car {
// instance variables
private String make;
private String model;
private int year;
private boolean isRunning;
//constructor
public Car(String make, String model, int year) {
this.make = make;
this.model = model;
this.year = year;
this.isRunning = false;
}
//method to start the car
public void start() {
isRunning = true;
System.out.println(year + " " + make + " " + model + " is now running.");
}
//method to stop the car
public void stop() {
isRunning = false;
System.out.println(year + " " + make + " " + model + " has stopped.");
}
//checking if the car is running
public boolean isCarRunning() {
return isRunning;
}
//set the year of the car
public void setYear(int newYear) {
year = newYear;
}
//retrieve the year of the car
public int getYear() {
return year;
}
//method to get the make of the car
public String getMake() {
return make;
}
//retrieve model of the car
public String getModel() {
return model;
}
}
public class CarExample {
public static void main(String[] args) {
// instance
Car myCar = new Car("Toyota", "Camry", 2023);
// call methods on the object
myCar.start();
System.out.println(myCar.getYear() + " " + myCar.getMake() + " " + myCar.getModel() + " is running.");
myCar.stop();
System.out.println(myCar.getYear() + " " + myCar.getMake() + " " + myCar.getModel() + " has stopped.");
// method to change the year of the car
myCar.setYear(2024);
System.out.println("Updated year of the car: " + myCar.getYear());
}
}
CarExample.main(null);
Explain Anatomy of a Class in comments of program (Diagram key parts of the class):
// class definition
class Car {
// instance variables
private String make;
private String model;
private int year;
private boolean isRunning;
//constructor
public Car(String make, String model, int year) {
this.make = make;
this.model = model;
this.year = year;
this.isRunning = false;
}
//method to start the car
public void start() {
isRunning = true;
System.out.println(year + " " + make + " " + model + " is now running.");
}
//method to stop the car
public void stop() {
isRunning = false;
System.out.println(year + " " + make + " " + model + " has stopped.");
}
//checking if the car is running
public boolean isCarRunning() {
return isRunning;
}
//set the year of the car
public void setYear(int newYear) {
year = newYear;
}
//retrieve the year of the car
public int getYear() {
return year;
}
// method to get the make of the car
public String getMake() {
return make;
}
//retrieve model of the car
public String getModel() {
return model;
}
}
In this code snippet, the anatomy of the Car class is explained with comments:
- The class is defined using the class keyword.
- It has instance variables (make, model, year, isRunning) that hold information about the car’s attributes.
- A constructor is defined with parameters (make, model, year) that initialize the instance variables.
- The class also contains other methods (not shown) to interact with the car object.
Comment for Class Definition and Object Instances:
// Class definition
class Car {
// instance variables
private String make;
private String model;
private int year;
private boolean isRunning;
//constructor
public Car(String make, String model, int year) {
this.make = make;
this.model = model;
this.year = year;
this.isRunning = false;
}
//other methods not included
}
public class CarExample {
public static void main(String[] args) {
// Instance
Car myCar = new Car("Toyota", "Camry", 2023);
//other code not included
}
//other code not included
}
In this code snippet, the anatomy of the Car class is explained with comments:
- The class is defined using the class keyword.
- It has instance variables (make, model, year, isRunning) that hold information about the car’s attributes.
- A constructor is defined with parameters (make, model, year) that initialize the instance variables.
- The class also contains other methods (not shown) to interact with the car object.
Comment in code where there is a definition of a Class and an instance of a Class (ie object):
// class definition
class Car {
//other code not included
}
//instantiate an object of the Car class
Car myCar = new Car("Toyota", "Camry", 2023);
| Car myCar = new Car("Toyota", "Camry", 2023);
constructor Car in class Car cannot be applied to given types;
required: no arguments
found: java.lang.String,java.lang.String,int
reason: actual and formal argument lists differ in length
- The class is defined with the comment “Class definition.”
- An instance of the Car class is created and assigned to the variable myCar.
- This line instantiates a new car object with the make “Toyota,” model “Camry,” and year 2023.
Comment in code where there are constructors and highlight the signature difference in the signature:
class Car {
public Car(String make, String model, int year) {
this.make = make;
this.model = model;
this.year = year;
this.isRunning = false;
}
}
- The comment “Constructor” indicates the presence of a constructor within the Car class.
- The constructor has a signature that includes three parameters: make (String), model (String), and year (int). This signature defines the inputs required to create an instance of the class.
Call an object method with a parameter (i.e., setters):
// method to set the year of the car
public void setYear(int newYear) {
year = newYear;
}
// call the setYear method with a new year value
setYear(myCar, 2024);
- The comment “Method to set the year of the car” identifies a method used for setting the year of the car object.
- The method takes a parameter newYear (int) that represents the new year value.
- The method is called later with the line “setYear(myCar, 2024);”, where myCar is the object on which the method is being called, and 2024 is the new year value being passed as an argument.
Additonal edit with creating print method
class Car {
private void printMessage(String message) {
System.out.println(message);
}
public void start() {
isRunning = true;
printMessage(year + " " + make + " " + model + " is now running.");
}
//method to stop the car
public void stop() {
isRunning = false;
printMessage(year + " " + make + " " + model + " has stopped.");
}
}
public static void main(String[] args) {
Car myCar = new Car("Toyota", "Camry", 2023);
myCar.start();
Car.printMessage(myCar.getYear() + " " + myCar.getMake() + " " + myCar.getModel() + " is running.");
myCar.stop();
Car.printMessage(myCar.getYear() + " " + myCar.getMake() + " " + myCar.getModel() + " has stopped.");
myCar.setYear(2024);
Car.printMessage("Updated year of the car: " + myCar.getYear());
}
Java Console Games Hacks
Make RPS, Tic-Tack-Toe, and Higher Lower into different cells and objects. Document each cell in Jupyter Notebooks.
RPS
Tic-Tack-Toe
Higher or Lower
Running Menu with Recursion vs. While Loop
import java.util.Scanner;
import java.util.Random;
import java.util.HashMap;
public class ConsoleGame {
public final String DEFAULT = "\u001B[0m"; // Default Terminal Color
public ConsoleGame() {
this.menuString();
Scanner sc = new Scanner(System.in); // using Java Scanner Object
this.processChoice(sc);
sc.close();
}
public void menuString() {
String menuText = ""
+ "\u001B[35m___________________________\n"
+ "|~~~~~~~~~~~~~~~~~~~~~~~~~|\n"
+ "|\u001B[0m Menu! \u001B[35m|\n"
+ "|~~~~~~~~~~~~~~~~~~~~~~~~~|\n"
+ "| 0 - Exit |\n"
+ "| 1 - Rock Paper Scissors |\n"
+ "| 2 - Higher or Lower |\n"
+ "| 3 - Tic Tac Toe |\n"
+ "|_________________________| \u001B[0m\n"
+ "\n"
+ "Choose an option.\n"
;
System.out.println(menuText);
}
public void processChoice(Scanner sc) {
try {
int choice = sc.nextInt(); // using method from Java Scanner Object
System.out.print("" + choice + ": ");
boolean quit = this.action(choice); // take action
if (!quit) {
this.processChoice(sc); //recursion
}
} catch (Exception e) {
sc.nextLine(); // error: clear buffer
System.out.println(e + ": Not a number, try again.");
this.processChoice(sc);
}
}
private boolean action(int selection) {
boolean quit = false;
switch (selection) { // Switch or Switch/Case is Control Flow statement and is used to evaluate the user selection
case 0:
System.out.print("Goodbye, World!");
quit = true;
break;
case 1:
RockPaperScissors rockpaperscissors = new RockPaperScissors();
rockpaperscissors.playGame();
break;
case 2:
HigherLower higherLowerGame = new HigherLower();
higherLowerGame.playGame();
break;
case 3:
ticTacToe();
break;
default:
//Prints error message from console
System.out.print("Unexpected choice, try again.");
}
System.out.println(DEFAULT); // make sure to reset color and provide new line
return quit;
}
public class HigherLower {
private final int maxNumber = 8;
private final Random random = new Random();
private final Scanner scanner = new Scanner(System.in);
private final ArrayList<Integer> previousGuesses = new ArrayList<>();
private final Map<Integer, String> comparisonMessages = new HashMap<>();
public HigherLower() {
comparisonMessages.put(-1, "higher");
comparisonMessages.put(0, "correct");
comparisonMessages.put(1, "lower");
}
public void playGame() {
System.out.println("Higher or Lower");
System.out.println("You have three guesses to guess the number I am thinking of between 1-8.");
System.out.println("If you guess the number correctly, you win!");
int targetNumber = random.nextInt(maxNumber) + 1;
int remainingGuesses = 3;
while (remainingGuesses > 0) {
System.out.print("Enter your guess: ");
int userGuess = scanner.nextInt();
if (previousGuesses.contains(userGuess)) {
System.out.println("You've already guessed that number. Try again.");
continue;
}
previousGuesses.add(userGuess);
int comparison = Integer.compare(userGuess, targetNumber);
System.out.println("The number is " + comparisonMessages.get(comparison));
if (comparison == 0) {
System.out.println("Congratulations! You guessed the number.");
return;
}
remainingGuesses--;
}
System.out.println("You're out of guesses. The number was " + targetNumber);
}
public void main(String[] args) {
HigherLower game = new HigherLower();
game.playGame();
}
}
public class RockPaperScissors {
private final String[] choices = {"rock", "paper", "scissors"};
private final Random random = new Random();
private final Scanner scanner = new Scanner(System.in);
private final HashMap<String, String> winningChoices = new HashMap<>();
public RockPaperScissors() {
winningChoices.put("rock", "scissors");
winningChoices.put("paper", "rock");
winningChoices.put("scissors", "paper");
}
public void playGame() {
System.out.println("Rock Paper Scissors");
System.out.println("Type r for rock, p for paper, or s for scissors");
String userChoice = getUserChoice();
String computerChoice = choices[random.nextInt(choices.length)];
determineWinner(userChoice, computerChoice);
}
private String getUserChoice() {
System.out.print("Your choice: ");
return scanner.nextLine().toLowerCase();
}
private void determineWinner(String userChoice, String computerChoice) {
System.out.println("You chose " + userChoice);
System.out.println("The computer chose " + computerChoice);
if (userChoice.equals(computerChoice)) {
System.out.println("It's a tie!");
} else if (winningChoices.get(userChoice).equals(computerChoice)) {
System.out.println("You win!");
} else {
System.out.println("You lose!");
}
}
public void main(String[] args) {
RockPaperScissors game = new RockPaperScissors();
game.playGame();
}
}
public void ticTacToe(){
System.out.println("Tic Tac Toe");
Scanner scTTT = new Scanner(System.in);
String[] board = {"1", "2", "3", "4", "5", "6", "7", "8", "9"};
String player = "X";
String player2 = "O";
int turn = 0;
Boolean quit = false;
System.out.println("Do you want to play against a friend or the computer?");
System.out.println("Type 1 for friend, 2 for computer");
int choice = scTTT.nextInt();
//make tic tac toe using player1 and player2
if(choice == 1){
System.out.println("Type the number of the square you want to place your piece in");
while(quit == false){
System.out.println("Player 1's turn (X)");
System.out.println(board[0] + " | " + board[1] + " | " + board[2]);
System.out.println(board[3] + " | " + board[4] + " | " + board[5]);
System.out.println(board[6] + " | " + board[7] + " | " + board[8]);
int move = scTTT.nextInt();
if(board[move - 1].equals("X") || board[move - 1].equals("O")){
System.out.println("That square is already taken, try again");
}
else{
board[move - 1] = player;
turn++;
if(board[0].equals("X") && board[1].equals("X") && board[2].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[3].equals("X") && board[4].equals("X") && board[5].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[6].equals("X") && board[7].equals("X") && board[8].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[0].equals("X") && board[3].equals("X") && board[6].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[1].equals("X") && board[4].equals("X") && board[7].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[2].equals("X") && board[5].equals("X") && board[8].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[0].equals("X") && board[4].equals("X") && board[8].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[2].equals("X") && board[4].equals("X") && board[6].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(turn == 9){
System.out.println("It's a tie!");
quit = true;
}
else{
System.out.println("Player 2's turn (O)");
System.out.println(board[0] + " | " + board[1] + " | " + board[2]);
System.out.println(board[3] + " | " + board[4] + " | " + board[5]);
System.out.println(board[6] + " | " + board[7] + " | " + board[8]);
int move2 = scTTT.nextInt();
if(board[move2 - 1].equals("X") || board[move2 - 1].equals("O")){
System.out.println("That square is already taken, try again");
}
else{
board[move2 - 1] = player2;
turn++;
if(board[0].equals("O") && board[1].equals("O") && board[2].equals("O")){
System.out.println("Player 2 wins!");
quit = true;
}
else if(board[3].equals("O") && board[4].equals("O") && board[5].equals("O")){
System.out.println("Player 2 wins!");
quit = true;
}
else if(board[6].equals("O") && board[7].equals("O") && board[8].equals("O")){
System.out.println("Player 2 wins!");
quit = true;
}
else if(board[0].equals("O") && board[3].equals("O") && board[6].equals("O")){
System.out.println("Player 2 wins!");
quit = true;
}
else if(board[1].equals("O") && board[4].equals("O") && board[7].equals("O")){
System.out.println("Player 2 wins!");
quit = true;
}
else if(board[2].equals("O") && board[5].equals("O") && board[8].equals("O")){
System.out.println("Player 2 wins!");
quit = true;
}
}
}
}
}
}
if(choice == 2){
String computer = "O";
System.out.println("Type the number of the square you want to place your piece in");
while(quit == false){
System.out.println("Player 1's turn (X)");
System.out.println(board[0] + " | " + board[1] + " | " + board[2]);
System.out.println(board[3] + " | " + board[4] + " | " + board[5]);
System.out.println(board[6] + " | " + board[7] + " | " + board[8]);
int move = scTTT.nextInt();
if(board[move - 1].equals("X") || board[move - 1].equals("O")){
System.out.println("That square is already taken, try again");
}
else{
board[move - 1] = player;
turn++;
if(board[0].equals("X") && board[1].equals("X") && board[2].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[3].equals("X") && board[4].equals("X") && board[5].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[6].equals("X") && board[7].equals("X") && board[8].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[0].equals("X") && board[3].equals("X") && board[6].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[1].equals("X") && board[4].equals("X") && board[7].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[2].equals("X") && board[5].equals("X") && board[8].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[0].equals("X") && board[4].equals("X") && board[8].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(board[2].equals("X") && board[4].equals("X") && board[6].equals("X")){
System.out.println("Player 1 wins!");
quit = true;
}
else if(turn == 9){
System.out.println("It's a tie!");
quit = true;
}
else{
System.out.println("Computer's turn (O)");
System.out.println(board[0] + " | " + board[1] + " | " + board[2]);
System.out.println(board[3] + " | " + board[4] + " | " + board[5]);
System.out.println(board[6] + " | " + board[7] + " | " + board[8]);
int move2 = (int)(Math.random() * 9) + 1;
if(board[move2 - 1].equals("X") || board[move2 - 1].equals("O")){
System.out.println("That square is already taken, try again");
}
else{
board[move2 - 1] = computer;
turn++;
if(board[0].equals("O") && board[1].equals("O") && board[2].equals("O")){
System.out.println("Computer wins!");
quit = true;
}
else if(board[3].equals("O") && board[4].equals("O") && board[5].equals("O")){
System.out.println("Computer wins!");
quit = true;
}
else if(board[6].equals("O") && board[7].equals("O") && board[8].equals("O")){
System.out.println("Computer wins!");
quit = true;
}
else if(board[0].equals("O") && board[3].equals("O") && board[6].equals("O")){
System.out.println("Computer wins!");
quit = true;
}
else if(board[1].equals("O") && board[4].equals("O") && board[7].equals("O")){
System.out.println("Computer wins!");
quit = true;
}
else if(board[2].equals("O") && board[5].equals("O") && board[8].equals("O")){
System.out.println("Computer wins!");
quit = true;
}
}
}
}
}
}
scTTT.close();
}
static public void main(String[] args) {
new ConsoleGame(); // starting Menu object
}
}
ConsoleGame.main(null);
[35m___________________________
|~~~~~~~~~~~~~~~~~~~~~~~~~|
|[0m Menu! [35m|
|~~~~~~~~~~~~~~~~~~~~~~~~~|
| 0 - Exit |
| 1 - Rock Paper Scissors |
| 2 - Higher or Lower |
| 3 - Tic Tac Toe |
|_________________________| [0m
Choose an option.
3: Tic Tac Toe
Do you want to play against a friend or the computer?
Type 1 for friend, 2 for computer
Type the number of the square you want to place your piece in
Player 1's turn (X)
1 | 2 | 3
4 | 5 | 6
7 | 8 | 9
Computer's turn (O)
X | 2 | 3
4 | 5 | 6
7 | 8 | 9
Player 1's turn (X)
X | 2 | 3
4 | 5 | 6
7 | O | 9
That square is already taken, try again
Player 1's turn (X)
X | 2 | 3
4 | 5 | 6
7 | O | 9
Computer's turn (O)
X | X | 3
4 | 5 | 6
7 | O | 9
Player 1's turn (X)
X | X | 3
O | 5 | 6
7 | O | 9
Player 1 wins!
[0m
4: Unexpected choice, try again.[0m
0: Goodbye, World![0m
Units in my Java Console Games
import java.util.Scanner;
import java.util.Random;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
public class ConsoleGame {
public final String DEFAULT = "\u001B[0m"; // Default Terminal Color
// Constructor
public ConsoleGame() {
this.menuString();
Scanner sc = new Scanner(System.in);
this.processChoice(sc);
sc.close();
}
// Menu display
public void menuString() {
//Unit: Printing and String manipulation
String menuText = ""
+ "\u001B[35m___________________________\n"
+ "|~~~~~~~~~~~~~~~~~~~~~~~~~|\n"
+ "|\u001B[0m Menu! \u001B[35m|\n"
+ "|~~~~~~~~~~~~~~~~~~~~~~~~~|\n"
+ "| 0 - Exit |\n"
+ "| 1 - Rock Paper Scissors |\n"
+ "| 2 - Higher or Lower |\n"
+ "| 3 - Tic Tac Toe |\n"
+ "|_________________________| \u001B[0m\n"
+ "\n"
+ "Choose an option.\n"
;
System.out.println(menuText);
}
// Processing user choice
public void processChoice(Scanner sc) {
// Unit: Input handling, recursion
try {
int choice = sc.nextInt();
System.out.print("" + choice + ": ");
boolean quit = this.action(choice);
if (!quit) {
this.processChoice(sc);
}
} catch (Exception e) {
sc.nextLine();
System.out.println(e + ": Not a number, try again.");
this.processChoice(sc);
}
}
// Handling user's chosen action
private boolean action(int selection) {
// Unit: Control flow, objects, method calls
boolean quit = false;
switch (selection) {
case 0:
System.out.print("Goodbye, World!");
quit = true;
break;
case 1:
RockPaperScissors rockpaperscissors = new RockPaperScissors();
rockpaperscissors.playGame();
break;
case 2:
HigherLower higherLowerGame = new HigherLower();
higherLowerGame.playGame();
break;
case 3:
ticTacToe();
break;
default:
System.out.print("Unexpected choice, try again.");
}
System.out.println(DEFAULT);
return quit;
}
public class HigherLower {
//Unit: Objects, fields, initialization
}
// Rock Paper Scissors game
public class RockPaperScissors {
//Unit: Objects, fields, initialization
}
public class ticTacToe() {
// Unit: Arrays, loops, conditional statements
// ...
}
}