I'm having an issue that I cannot seem to fix. My goal is to prompt the user for the number of people playing the game. I want to continue prompting the user while their input meets the following requirements:
-input is not an integer
-input is less than three
-input is larger than seven
What is happening is that it seems to require 3 inputs to check the third condition, one for the first and two for the second. It is not checking them all at once, and I assume it has something to do with the syntax .nextInt(), but I cannot find another way to express this. Thank you ahead of time for your help!
Here is the code:
public void setNumPlayers(Game game) {
Scanner input = new Scanner(System.in);
System.out.println("How many people are playing?");
while(!input.hasNextInt() || input.nextInt() < 3 || input.nextInt() > 7) {
System.out.println("Please eneter the number of people playing. You must have at least three players, and no more than seven.");
input.next();
}
game.setNumPlayers(input.nextInt());
input.close();
}
and the call in the main
Game g = new Game();
ConsoleOutput io = new ConsoleOutput();
io.setNumPlayers(g);
System.out.println(g.getNumPlayers());
EDIT:
I've changed the code to store the nextInt as a variable. The following code works, prompts me if I enter letters, prompts me and lets me reassign x if I enter a number outside of its parameters, the only issue is that If I enter an incorrect number, THEN a letter, it crashes...should I encapsulate this in some kind of a try/catch? That doesnt seem practical.
public void setNumPlayers(Game game) {
Scanner input = new Scanner(System.in);
System.out.println("How many people are playing?");
while(!input.hasNextInt()) {
System.out.println("Please eneter the number of people playing.");
input.next();
}
int x = input.nextInt();
while(x<3 || x>7) {
System.out.println("The number of players must be at least three and no more than seven.");
x = input.nextInt();
}
game.setNumPlayers(x);
input.close();
}
You have to modify a little bit the logic, if you want to check input and continue to ask to enter until the input is good. The following will work for a sequence of inputs like:
How many people are playing?
Please enter the number of people playing. You must have at least three players, and no more than seven.
10
Please enter the number of people playing. You must have at least three players, and no more than seven.
toto
Please enter the number of people playing. You must have at least three players, and no more than seven.
tutu
Please enter the number of people playing. You must have at least three players, and no more than seven.
22
Please enter the number of people playing. You must have at least three players, and no more than seven.
6
Scanner input = new Scanner(System.in);
System.out.println("How many people are playing?");
int numPlayers = 0;
while (numPlayers < 3 || numPlayers > 7) {
System.out.println("Please enter the number of people playing. You must have at least three players, and no more than seven.");
if (!input.hasNextInt()) {
input.next();
}
else {
numPlayers = input.nextInt();
}
}
game.setNumPlayers(numPlayers);
input.close();
By calling Scanner.nextInt() twice, you read two numbers, not the same one twice.
Consider reading the int value, store it in a variable and use that in your if statement.
use && operator. and also use a local variable and assign the value from scanner. and use it in condition.
int x =0;
if(input.hasNextInt())
{
x= input.nextInt();
}
while( x > 3 && x < 7) {
System.out.println("Please eneter the number of people playing. You must have at least three players, and no more than seven.");
input.next();
}
Related
I'm currently working on an assignment for school and I am almost done but I just have one large problem I need to fix before I can add the final bit.
I need to create a program that prompts you to enter either 1 or 2, Afterwards it asks you to enter three words/names and saves them into an array.
Then, depending on whether you picked 1 or 2, it prints them in alphabetical order or flips around the lowercase and uppercase letters. I didn't add that part yet because I'm trying to fix a problem related to the very first input.
When you input a number other than 1 or 2, I am instructed to display an error message and ask for input again. I am pretty sure what I need to do is get the entire program to go back to the beginning because copy/pasting the entire program again would be bad, lol
A big problem is probably that I'm using if/else statements with for loops inside when I might need to put the entire thing inside a loop? But I'm not sure what condition I would use to start the loop if I put the entire code in it. I must be missing something here.
With what I have now, it gets stuck saying invalid input even if you put in a 1 or 2.
import java.util.Scanner;
public class IsabellaPiantoniLab5 {
public static void main (String[]args) {
//Ask for input
Scanner input = new Scanner(System.in);
System.out.print("Please choose either a number 1 or number 2.");
int numChoice = input.nextInt();
//if choice is 1 or 2
if (numChoice == 1 || numChoice == 2) {
System.out.println("Please enter three names: ");
String nameInput[] = new String[4];
//input loop
for (int i= 0; i < nameInput.length; i++) {
nameInput[i] = input.nextLine();
}
System.out.println("Values are:");
//display values if 1
if (numChoice == 1) {
for (int i=1; i<4; i++) {
System.out.println(nameInput[i]);
}
}
//display values if 2
else if (numChoice == 2) {
for (int i=1; i<4; i++) {
System.out.println(nameInput[i]);
}
}
}
//retry if invalid------i restart from the beginning if this happens
else if (numChoice != 1 || numChoice != 2) {
System.out.println("Invalid value. Please try again.");
//continue;
}
}
}
System.exit(0);
This will terminate the app, thus you can start it again using command line ( START [your app path])
Or
RunTime.getRuntime().exec(“Your app”);
System.exit(0);
Edit I misunderstood the question, I thought you wanted to restart the whole app
After discussing the approach with #csm_dev
It is way either to ask for the user input one more time by emptying the field and showing a message “please enter a valid input” with a clarification message
So I'm new to java programming, coming from Python, and there's a few concepts that I can't quite understand.
I'm writing a program which allows the user to enter as many numbers as they want and the program should output the average of all of the numbers. I used a while loop to loop through the inputs by the user as many times as they wanted, but I needed a way of exiting the loop so that the program could proceed with calculating the average of all of the inputs. I decided that if the user enters an "=" sign instead of a number, then the program would break out of the loop, but since the Scanner variable was looking for a double, and the "=" sign is not a number, I would have to make it a String. But because the Scanner is looking for a double, the program threw an error when it encountered the "=".
How can I get the program to exit the loop when the user types "="? I know I could just allow the user to enter a number that breaks the loop, but if it was a real world program and the user entered a number, it would count that number along with the previous ones when calculating the average. The code I have so far is as follows:
import java.util.Scanner;
// imports the Scanner class
public class Average{
public static void main(String[] args){
double num, total = 0, noOfInputs = 0, answer;
Scanner scanner = new Scanner(System.in);
while(true){
System.out.print("Enter number: ");
//Prompts the user to enter a number
num = scanner.nextDouble();
/*Adds the number inputted to the "num" variable. This is the
source of my problem*/
if(num.equals("=")){
break;}
/*The if statement breaks the loop if a certain character is
entered*/
total = total + num;
//Adds the number inputted to the sum of all previous inputs
noOfInputs++;
/*This will be divided by the sum of all of the numbers because
Number of inputs = Number of numbers*/
}
answer = total / noOfInputs;
System.out.print(answer);
}
}
Several ways to do this.
You could read every number as a string, and then if it is a number, parse it to get the value.
Integer.parseInt(String s)
Or you could check what comes next and read accordingly:
while (scanner.hasNext()) {
if (sc.hasNextInt()) {
int a = scanner.nextInt();
} else if (scanner.hasNextLong()) {
//...
}
}
Or you could just catch the InputMismatchException, and work from there.
try{
...
} catch(InputMismatchException e){
//check if '=' ...
}
Now I know that there is a thread called "Validating input using java.util.Scanner". I already looked there and that thread only answered 1/2 of my problems. The other half is when someone enters a number greater than 2 I get Array Index Out of Bounds Exception. I just need help on if someone enters a 3 for either row or column, the console should prompt something like this:
"Enter the coordinates to place an 'X'. Row then Column."
//enters 3 and 3
"Please enter a valid input"
It would keep and asking the user for a valid number until he gives one.
Would I need to do something like the !keyboard.hasNextInt() but for integers? And that would run smoothly with the rest of my code?
You could use a do-while loop. Something like
do {
//prompt
//input
} while (input not valid);
Where prompt and input should be replaced by code to prompt the user and accept input. In the while section, check if input is valid.
You're question isn't too clear but I'll try to make sense of it.
I'm assuming you've named your scanner "keyboard"
Before I try running this code, the first problem I can see is this (Note that I grabbed this from your code before you edited the question):
while (board[row][col] != ' ')
{
System.out.println("Already occupied space");
System.out.println("Choose again");
row = keyboard.nextInt();
col = keyboard.nextInt();
}
Earlier, you made sure that the user enters integers. However, you have abandoned that completely in this case.
Assuming you're trying to avoid an error if the user enters something other than an integer, this is what I would do:
while(true){
boolean valid = true;
if(!keyboard.hasNextInt()){
valid = false;
keyboard.next();
}
else{
row = keyboard.nextInt();
}
if(!keyboard.hasNextInt()){
valid = false;
keyboard.next();
}
else{
col = keyboard.nextInt();
}
if (valid && (row > 2 || col > 2)){
System.out.println("Please enter a valid input");
continue;
}
else if(!valid){
System.out.println("Please enter a valid input");
continue;
}
else
break;
}
There are a couple reasons this code might seem a bit long. First off, we're trying to test if the input is an integer before we attempt to store it as an int. Secondly, we want to compare the input after we store it successfully to see if it's less than 3. If the input isn't an integer, the boolean "valid" will be false. The way a compiler works, if valid is false in the if statement it will ignore anything to the right of the &&, avoiding an error.
I admit, this is using some commands that I haven't learned before, so this might not be the most efficient way. But you get the idea :)
P.S. You should probably throw the above code into a method.
Any possible way to keep entering numbers, and when the same number is entered 2 or more times an error message arises or something like that? I need this to be answered in Java only. I'm new and I don't know where to go from here. I need help searching values in the array and then printing out all the numbers that have been entered.
public class Test
{
public static void main(String args[])
{
Scanner input = new Scanner(System.in);
System.out.println("How big is the group?: ");
int[] group = new int[input.nextInt()];
for (int i = 0; i < group.length; i++)
{
System.out.println("Please enter number: ");
group[i] = input.nextInt();
}
I think this is what you're looking for. Inside of the for loop, there's a while loop spinning to keep collecting new ints until you enter one that's not already in the list.
for (int i = 0; i < group.length; i++)
{
System.out.println("Please enter number: ");
int next = input.nextInt();
while(Arrays.asList(group).contains(next)) { // Keep asking for new input while the input is already in list
System.out.println("That number is already in the group ... try again.");
next = input.nextInt();
}
group[i] = next;
}
Since this is clearly a "learning exercise", it is only appropriate to give you hints:
You can search an array by stepping through the array indexes and testing the elements at each index.
A method and a class both need a closing } ...
I need this to be answered in Java only.
That is incorrect. What you REALLY need is some hints. If we give you Java code, you miss out on the important learning experience of writing it yourself. And THAT is the WHOLE POINT of the homework. Go ask your teacher if you don't believe me.
I'm making a console-based game of black jack that prompts the user asking him/her if he/she wants to: 'h' for hit, 's' for stay, or 'q' for quit. I'm using the Scanner class to receive input from the user in a while loop. The code works the first time it prompts the user and receives input, but it never works the second time. After the second prompt comes up, no matter what the user types, the program just waits and does nothing even though it's still running. I've been trying to get this to work for hours and have read the Java Docs, many SO questions, etc. Here's the relevant code:
public void gameloop() {
while (thedeck.cards.size() >= 1) {
prompt();
}
}
public void prompt() {
String command = "";
Boolean invalid = true;
System.out.println("Enter a command - h for hit, s for stay, q for quit: ");
Scanner scanner = new Scanner(System.in);
while (invalid) {
if (scanner.hasNext()) {
command = scanner.next();
if (command.trim().equals("h")) {
deal();
invalid = false;
} else if (command.trim().equals("s")) {
dealerturn();
invalid = false;
} else if (command.trim().equals("q")) {
invalid = false;
System.exit(0);
} else {
System.out.println("Invalid input");
scanner.next();
}
}
}
scanner.close();
}
Here's what the code outputs:
Dealer has shuffled the deck.
Dealer deals the cards.
Player's hand:
Three of Clubs: 3
Five of Clubs: 5
Enter a command - h for hit, s for stay, q for quit:
h
Dealer deals you a card:
Player's hand:
Three of Clubs: 3
Five of Clubs: 5
Queen of Hearts: 10
Enter a command - h for hit, s for stay, q for quit:
h (Program just stops here, you can keep entering characters,
but it does nothing even though the code is still running)
Any idea as to what's going wrong would be greatly appreciated. I also realize the while loop is a little ugly, but I just want to get this program in working condition before I start to revamp any code.
From the documentation for Scanner.close:
When a Scanner is closed, it will close its input source if the source implements the Closeable interface.
Here you close your scanner, and this causes System.In to be closed, which means you can't read any more input:
scanner.close();
It is better to open the scanner once and reuse it. Close it only when are sure you have finished reading all input, or are closing your application.