Here is my error message:
Exception in thread "main" java.lang.IllegalArgumentException: n must be positive
at java.util.Random.nextInt(Random.java:265)
at Game.generateSecretNumber(Game.java:44)
at Game.start(Game.java:32)
at Game.main(Game.java:18
My Code is:
import java.util.Random;
import java.util.Scanner;
public class Game {
private final int LOWER_BOUND = 1;
private int secretNumber;
private int top;
private static enum Response {YES, NO}
private Random random;
private Scanner scanner;
public static void main(String[] args) {
Game GuessingGame = new Game();
GuessingGame.start();
}
public Game() {
random = new Random( );
scanner = new Scanner(System.in);
}
public void start() {
Response answer;
answer = Response.YES;
while (answer == Response.YES) {
generateSecretNumber();
playGame();
answer = prompt("");
}
System.out.println("Bye!");
}
private void generateSecretNumber() {
secretNumber = random.nextInt(top) + 1;
System.out.println("You are going to guess a number between 1 and what number? ");
top = scanner.nextInt();
System.out.println("Type a number between 1 and: " + top);
}
private void playGame() {
int guessCount = 0;
int guess;
do {
guess = getNextGuess();
guessCount++;
if (guess < secretNumber) {
System.out.println("Too low. Try again:");
}
else if
(guess > secretNumber) {
System.out.println("Too high. Try again:");
}
}
while ( guess != secretNumber );
if ( guess == secretNumber ) {
System.out.println("Right! It took you " + guessCount + " tries");
}
else {
System.out.println("game over");
}
}
private Response prompt(String question) {
String input;
Response response = Response.NO;
System.out.print(question + "Would you like to play again? ");
input = scanner.next();
if (input.equals("Y") || input.equals("y")) {
response = Response.YES;
}
return response;
}
private int getNextGuess() {
int input;
while(true) {
System.out.print(" ");
input = scanner.nextInt();
if (LOWER_BOUND <= input && input <= top) {
return input;
}
System.out.println("Invalid input: " + "must be between " + LOWER_BOUND + " and" + top);
}
}
}
On first invocation top
is zero, so random.nextInt(top)
throws an exception. This method must only be called with positive numbers.
When you invoke: random.nextInt(top)
at line: 44, youre passing 0 ( for that's the value of the "top" variable )
You have to pass something > 0
That's what the: "n must be positive" means.
You use
secretNumber = random.nextInt(top) + 1;
before top
has been assigned a meaningful value (apart from the default 0
value ; random throws an exception since it needs a positive value).
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