Question RE: guessing game example in Head First Java

[Christopher Laurenzano]

I'm trying out the guessing game example in Ch. 2 of Head First Java. I've copied it and saved it (I like to do this, maybe to help get a feel for what's going on). I've saved it all on one file called GuessGame: Here's the code :

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 tragetNumber = (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; //game over, so break out of the loop
				} else {
				//we must keep going because nobody got it right!
				System.out.println("Players will have to try again.");

			}//end if/else
		}//end loop
	}//end method
}//end class

	
public class Player {
	int number = 0; // where the guess goes
	
	public void guess () {
		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 ();
	}
}
    

This is the entire program -- I have them saved as separate classes, so it compiled and ran fine. What I'd like to know is what does the while (true) condition mean in line 22? I know it has something to do with the booleans, but I'm not sure how to interpret the statement. What is going on that causes it to execute the statement inside the while loop?

[Jeanne Boyarsky]

Christopher Laurenzano wrote: What I'd like to know is what does the while (true) condition mean in line 22?

Normally when you have a loop, you write a condition inside the parens that evaluates to true or false which Java uses to determine whether to execute the loop another time. This example, always evaluates to true so Java always goes on to another loop execution.

The "break" in the loop is so this doesn't go on forever. When "break" is encountered, Java continues execution after the loop.

[Christopher Laurenzano]

I'm not sure I asked my question correctly --

I meant to ask what does true refer to, or what condition is being evaluated that is either true or false? Is it evaluating the values of the p1isRight - p3isRight variables? or is it something else, because there are no other boolean variables/values in the file.

[Jeanne Boyarsky]

True is the expression it is evaluating. Needless to say, it evaluates to the boolean true.

[Fred Hamilton]

true is just what it is, true. It is a boolean expression that always evaluates to true. It refers to nothing except itself.

Ok two almost identical answers. Jeanne beat me to it

[Nitish Bangera]

Actually these sort of things are mostly used in threads. If you want a thread to look at or get a value endlessly. While always requires a boolean value. SO inside a while, all expressions should evaluate to a boolean i.e in other words expressions are references to a boolean value in a loop. This may not sound good but its just hypothetical. So while(true) is a way of telling, run as much as you want like a never ending loop. Only way to get out of the loop is break, return and System.exit().