Head First Java Book, Chapter 2

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...

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..

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

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

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.

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...

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.

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

maybe a problem with my Java version?

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