Head First Java Book, Chapter 2

[brian hague]

Hello,

this is my first post

I'm in the guessing Game in Chapter 2 of Head First Java (page 39).

Here's the code I've got entered:

public class GuessGame {
	Player p1;
	Player p2;
	Player p3;
	
	public void startGame(){
		p1 = new Player();
		p2 = new Player();
		p3 = new Player();

		int guessp1 = 0;
		int guessp2 = 0;
		int guessp3 = 0;

		boolean p1isRight = false;
		boolean p2isRight = false;
		boolean p3isRight = false;

		int targetNumber = (int) (Math.random() * 10);
		System.out.println("I'm thinking of a number between 0 and 9...");

		while (true){
			System.out.println("Number to guess is " + targetNumber);

			p1.guess();
			p2.guess();
			p3.guess();

			guessp1 = p1.number;
			System.out.println("Player one guessed " + guessp1);

			guessp2 = p2.number;
			System.out.println("Player two guessed " + guessp2);

			guessp3 = p3.number;
			System.out.println("Player one guessed " + guessp3);

			if (guessp1 == targetNumber) {
				p1isRight = true;
			}
			if (guessp2 == targetNumber) {
				p2isRight = true;
			}
			if (guessp3 == targetNumber) {
				p3isRight = true;
			}

			if (p1isRight || p2isRight || p3isRight) {
				System.out.println("We have a winner!");
				System.out.println("Player one got it right?" + p1isRight);
				System.out.println("Player two got it right?" + p2isRight);
				System.out.println("Player three got it right?" + p3isRight);
				System.out.println("Game is over.");
				break;
			} else {
				System.out.println("Players will have to try again.");
			}
		}
	}
}

public class Player {
	int number;

	public void guess(){
		int number = (int) (Math.random() * 10);
		System.out.println("I'm guessing " + number);
	}
}

public class GameLauncher {
	public static void main(String[] args){
		GuessGame game = new GuessGame();
		game.startGame();
	}
}    

now in the GuessGame class, where guessp1 = p1.number; it's not assigning the value from p1.number to guessp1. (also p2 and p3)... just look at 29-35

A workaround would of course be to return a value from p1.guess, but that's not the point of doing OO... is it?

Mind you this isn't exactly the way I would have coded it, I'm just new to java (just started about 1 hour ago...)... actually I worked with Java 1.02 in school, when it first came out... freakishly slow... the newer version is much better...

[Harshit Rastogi]

now in the GuessGame class, where guessp1 = p1.number; it's not assigning the value from p1.number to guessp1. (also p2 and p3)... just look at 29-35

I believe thats what it is doing. correct me if my understanding is wrong..

[brian hague]

it's supposed to give it the value of p1.number, but when it's compiled and run it takes a value of 0.

[Campbell Ritchie]

Where did you initialise p1.number? If you don't initialise a number primitive field it will have 0 as a default value.

[brian hague]

 public class Player {  
     int number;  
   
     public void guess(){  
         int number = (int) (Math.random() * 10);  
         System.out.println("I'm guessing " + number);  
     }  
 }      

In the Player class, number was initialized as int number = 0;, however right now it's not... . previous to p1.number, it calls p1.Guess(), which is supposed to assign a value to the variable 'number' on line 5 above.

right now the program will loop unless the first RNG also has a value zero, regardless of whether or not the Player.Guess() assigns a value to Player.number.

I've been reading ahead in the book, and it looks like int number should be in private, then have Guess return a number, or have a second function return a stored value... encapsulation. In this example, however, they don't use encapsulation since it hasn't been introduced yet.

[brian hague]

I've made some changes to the code... based on what I've learned from chapters 3-5... I would still like to understand why the variable was not able to assign a value from a public class variable...

GameLauncher.java

 public class GameLauncher {
	public static void main(String[] args){
		GuessGame game = new GuessGame();
		game.startGame();
	}
}

Player.java

 public class Player {
	private int number = 0;

	public int guess(){
		number = (int) (Math.random() * 10);
		System.out.println("I'm guessing " + number);
		return number;
	}
}

GuessGame.java

 public class GuessGame {
	Player p1;
	Player p2;
	Player p3;
	
	public void startGame(){
		p1 = new Player();
		p2 = new Player();
		p3 = new Player();

		int guessp1 = 0;
		int guessp2 = 0;
		int guessp3 = 0;

		boolean p1isRight = false;
		boolean p2isRight = false;
		boolean p3isRight = false;

		int targetNumber = (int) (Math.random() * 10);
		System.out.println("I'm thinking of a number between 0 and 9...");

		while (true){
			System.out.println("Number to guess is " + targetNumber);

			guessp1 = p1.guess();
			guessp2 = p2.guess();
			guessp3 = p3.guess();

			//guessp1 = p1.number;
			System.out.println("Player one guessed " + guessp1);

			//guessp2 = p2.number;
			System.out.println("Player two guessed " + guessp2);

			//guessp3 = p3.number;
			System.out.println("Player one guessed " + guessp3);

			if (guessp1 == targetNumber) {
				p1isRight = true;
			}
			if (guessp2 == targetNumber) {
				p2isRight = true;
			}
			if (guessp3 == targetNumber) {
				p3isRight = true;
			}

			if (p1isRight || p2isRight || p3isRight) {
				System.out.println("We have a winner!");
				System.out.println("Player one got it right?" + p1isRight);
				System.out.println("Player two got it right?" + p2isRight);
				System.out.println("Player three got it right?" + p3isRight);
				System.out.println("Game is over.");
				break;
			} else {
				System.out.println("Players will have to try again.");
			}
		}
	}
}

hopefully this will help anyone else who is reading this book...

[Brian Pianczk]

But you haven't actually changed the functionality of the code? It is still taking Player.number and creating a random number in the Player.guess method. It doesn't matter if the instance variable is public and you use a void method, or the instance variable is private and you use a return method. You still get the same result, just your second example protects the instance variable.

I went through this chapter last week, and didn't experience your initial problem.

[brian hague]

That's why I'm posting this here... It's not doing what it should...

maybe a problem with my Java version?

[Henry Wong]

Take a look at you guess() method again. The issue is that you accidently declared a local variable "number", instead of just assign the random number to the instance variable "number".

Henry