So, I want to receive input from the user, check if they used alphabetical values and then check if it is too long. If too long, I want to start again from the top (checking if alphabetical) by calling the method I am in. However, when I start over and I type, say "Danny", this will show:
Output: "Thank you, got Danny"
Output: (length of previous, too long input) + "is too many characters, try to keep it under 30."
So somehow, it keeps the original input (that was alphabetical, but above 30) saved and it doesn't alter it when it starts over. Anyone know what I should do instead?
public static String inputPattern() {
Scanner scanner = new Scanner(System.in);
String player;
int strLength;
System.out.println("Please enter your name:");
while (!scanner.hasNext("[A-Za-z]+")) { //Checks if alphabetical value
System.out.println("Please stick to the alphabet!");
scanner.next();
}
player = scanner.next();
player += scanner.nextLine();
System.out.println("Thank you! Got " + player);
strLength = player.length(); // Saves the length of user-inputted name
while (strLength > 30) { // Checks if not too long
System.out.println(strLength + " is too many characters, please try to keep it under 30");
inputPattern(); // Starts over again if too long
}
return player;
}
I have taken your method and modified it a bit.
It is non recursive solution.
Also in your code scanner resource was not closed at the end.
Iterative Solution
import java.util.Scanner;
public class SO66064473 {
public static void main(String[] args) {
inputPatternIterative();
}
public static String inputPatternIterative() {
Scanner scanner = new Scanner(System.in);
String player = "";
int strLength = Integer.MAX_VALUE;
while (strLength > 30) { // Checks if not too long
System.out.println("Please enter your name:");
while (!scanner.hasNext("[A-Za-z]+")) { //Checks if alphabetical value
System.out.println("Please stick to the alphabet!");
scanner.next();
}
player = scanner.next();
player += scanner.nextLine();
System.out.println("Thank you! Got " + player);
strLength = player.length(); // Saves the length of user-inputted name
if (strLength > 30)
System.out.println(strLength + " is too many characters, please try to keep it under 30");
}
scanner.close(); // Closing scanner resource after use.
return player;
}
}
Output :
Please enter your name:
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Thank you! Got aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
70 is too many characters, please try to keep it under 30
Please enter your name:
aaaaaaaaaaaaaaaaaaaa12
Please stick to the alphabet!
coifvoifoivmrfvoirvoirovroijfoirjfoijroifjrwofjorwfouwrfoijwrofjworjfoiwrjf
Thank you! Got coifvoifoivmrfvoirvoirovroijfoirjfoijroifjrwofjorwfouwrfoijwrofjworjfoiwrjf
75 is too many characters, please try to keep it under 30
Please enter your name:
Danny
Thank you! Got Danny
EDIT : with the suggestion made by #Dev-vruper here is updated easy recursive code
Recursive Solution
import java.util.Scanner;
public class SO66064473 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
inputPatternRecursive(sc);
sc.close();
}
public static String inputPatternRecursive(Scanner sc) {
System.out.println("Please enter your name:");
String player = sc.nextLine();
if (!player.matches("[A-Za-z]+")) {
System.out.println("Please stick to the alphabet!");
inputPatternRecursive(sc);
} else {
System.out.println("Thank you! Got " + player);
if (player.length() > 30) {
System.out.println(player.length() + " is too many characters, please try to keep it under 30");
inputPatternRecursive(sc);
}
}
return player;
}
}
This should solve your problem in a pretty easy way:
public static String inputPattern(){
Scanner scanner = new Scanner(System.in);
String player = "";
int strLength;
boolean bShowedInstruction = true;
System.out.println("Please enter your name:");
while (true) {
if (!bShowedInstruction)
System.out.println("Please enter your name:");
bShowedInstruction = false;
player = scanner.next();
if (!player.matches("[A-Za-z]+")) {
System.out.println("Please stick to the alphabet!");
}
else if (player.length() > 30) {
System.out.println(player.length() + " is too many characters, please try to keep it under 30!");
}
else
break;
}
System.out.println("Thank you! Got " + player);
return player;
}
There's no need for a recursion. A simple while(true) loop does the trick.
It's a pretty clean solution keeping unnecessary scan-methods out of the game.
Related
I am currently experimenting with Java, trying to get the user to input an integer. If the user doesn't enter an integer I want a message to appear saying "You need to enter an Integer: " with a completely new input field to the original one.
Code:
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
Scanner inputScanner = new Scanner(System.in);
int counter = 0;
boolean run = true;
int userInput = 0;
while (run) {
System.out.print("Enter an integer: ");
if (inputScanner.hasNextInt()) {
userInput = inputScanner.nextInt();
} else if (!inputScanner.hasNextInt()) {
while (!inputScanner.hasNextInt()) {
System.out.print("You need to enter an Integer: ");
userInput = inputScanner.nextInt();
}
}
System.out.println(userInput);
if (counter == 6) {
run = false;
}
counter++;
}
}
}
At the moment the code above gives an Exception error ("java.util.InputMismatchException"). I have tried to use a try/catch but this doesn't really work because I want the user to see the second message ("You need to enter an Integer") everytime they don't enter an integer and I don't want it to re-loop around the main run loop for the same reason. I'm sure there is a better way to do this, however I am not sure of it. Any help will be massively appreciated, thanks in advance.
In this case it would make more sense for the Scanner to use hasNextLine and then convert the String to an Integer. If that you could do something like this:
try {
new Integer(inputScanner.hasNextLine);
} catch (Exception e) {
System.out.println(“<error message>”)
}
In place of the if(inputScanner.hasNextInt()) due to the fact that the hasNextInt function will error out if there is not an Integer to be read.
I am working on a school project that basically allows the user to create, edit or view students. Once a student is created, they each get assigned a unique ID like 1, 2, 3, etc. All the functionally of creation, editing and displaying is working but I am stuck on have to give them a unique ID after created. Here is the code I have and in the // commented areas is what I attempted to do but I am not sure if its right. Any ideas will be very appreciated.
import java.util.Scanner;
import java.io.*;
public class MidTermProject {
public static void main(String[] args) throws IOException {
Scanner keyboard = new Scanner(System.in);
System.out.println("Here is the sample of menu choices for Main Menu.");
System.out.println("\nWelcome to University Enrollment" + "\n1. Create Student" + "\n2. Edit Student" + "\n3. Display Student" + "\n0. --- Quit ---");
System.out.println("Please enter a valid choice(1-10, 0 to Quit) :");
int userInput = keyboard.nextInt();
if(userInput == 1) {
CreateStudent();
} else if(userInput == 2) {
EdithStudent();
} else if(userInput == 3) {
DisplayStudent();
} else if(userInput == 0) {
System.out.print("Done");
} else {
System.out.println("Invalid Option, Please try again.");
userInput = keyboard.nextInt();
if(userInput == 1) {
CreateStudent();
} else if(userInput == 2) {
EditStudent();
} else if(userInput == 3) {
DisplayStudent();
} else if(userInput == 0) {
System.out.print("Done");
}
}
}
public static void CreateStudent() throws IOException {
String FullName;
String address;
String city;
String state;
int StudentID;
Scanner keyboard = new Scanner(System.in);
FileOutputStream fstream =
new FileOutputStream("StudentInfo.dat");
DataOutputStream outputFile =
new DataOutputStream(fstream);
System.out.print("\nPlease enter your information bellow.\n" + "\nFull Name: ");
FullName = keyboard.nextLine();
outputFile.writeUTF(FullName);
System.out.print("Address: ");
address = keyboard.nextLine();
outputFile.writeUTF(address);
System.out.print("City: ");
city = keyboard.nextLine();
outputFile.writeUTF(city);
System.out.print("State: ");
state = keyboard.nextLine();
outputFile.writeUTF(state);
//allowed the user to select their own ID number
System.out.print("Please get a Student ID(1-10): ");
//Store the selected number on StudentID
StudentID = keyboard.nextInt();
//The for loop will increment index each time a user is created
for(int index = 0; index == StudentID; index++) {
//The if statement will compare index and StudentID, if equal will ask the user to enter a different number
if(index == StudentID) {
System.out.print("The selected ID has been selected already, Please select a different ID");
StudentID = keyboard.nextInt();
}
}
//write the number in the file
outputFile.writeInt(StudentID);
System.out.print("Successfully Created");
}
public static void EditStudent() throws IOException {
String editName;
String editaddress;
String editCity;
String editState;
Scanner keyboard = new Scanner(System.in);
RandomAccessFile file =
new RandomAccessFile("StudentInfo.dat", "rw");
file.seek(0);
System.out.print("\nPlease enter NEW information bellow.\n" + "\nFull Name: ");
editName = keyboard.nextLine();
file.writeUTF(editName);
System.out.print("Address: ");
editaddress = keyboard.nextLine();
file.writeUTF(editaddress);
System.out.print("City: ");
editCity = keyboard.nextLine();
file.writeUTF(editCity);
System.out.print("State: ");
editState = keyboard.nextLine();
file.writeUTF(editState);
file.close();
System.out.print("Successfully Edited");
}
public static void DisplayStudent() throws IOException {
FileInputStream fstream = new FileInputStream("StudentInfo.dat");
DataInputStream inputFile = new DataInputStream(fstream);
String student;
boolean endOfFile = false;
while(!endOfFile)
{
try
{
student = inputFile.readUTF();
System.out.print(student + " ");
}
catch (EOFException e)
{
endOfFile = true;
}
}
System.out.println("\nDone");
inputFile.close();
}
Firstly, following Java naming conventions makes your code more readable. So use lowercase first when naming a variable: studentId rather than StudentId. Initial-caps is for class names.
In your create student method, your for loop makes no sense.
for(int index = 0; index == StudentID; index++) {
//The if statement will compare index and StudentID, if equal will ask the user to enter a different number
if(index == StudentID) {
System.out.print("The selected ID has been selected already, Please select a different ID");
StudentID = keyboard.nextInt();
}
}
A for loop simply increments the index defined in the first clause, stepping the increment according to the third clause, until the second clause proves true.
So in your code, if the user enters 4, your loop counts 0, 1, 2, 3, 4 «bingo». Now that we reached the user’s specified number, we go on to ask them for another number. And we’re done. But that process is illogical.
That code fails to accomplish your goal of checking for existing students. You need to review all existing students one-by-one. Compare each existing student ID against the desired ID. Only after exhausting the list of all known students should we use the desired ID. If we find a match on an existing student, then we break out of the loop to ask the user for another choice of ID. And we need another outer loop to continue this “ask, search, ask again if needed” process until an unused desired ID is determined.
Big tip: If you write out your problem statement and solution attempt as plain prose, similar to what I just did in the paragraph above, your programming will go more smoothly. And your written prose will be fodder for writing helpful comments in your source code.
I'm bulding a console application where I am trying to force a user to enter an int as a possible answer to a question otherwise the same question is repeated to the user.Thus, the user cannot move on without entering the proper data type.
below is my sample code.
Scanner scanner = new Scanner(System.in);
int userInput = 0;
do {
AskQuestion();
if(scanner.hasNextInt()) {
userInput = scanner.nextInt();
}
}
while(!scanner.hasNextInt()) ;
While I know this can be done in C#, I'm not exactly sure how to do it in java without getting stuck in an infinite loop. How do I get my code to do what I want to do? Please help!
You can use something like this. It'a a pretty simple flag combined with the use of the Scanner class.
boolean flag = false;
int val = 0;
while(!flag){
System.out.println("Something");
if(sc.hasNext()){
if(sc.hasNextInt()){
val = sc.nextInt();
flag = true;
}
else{
sc.next();
}
}
}
Try this:
Scanner scanner = new Scanner(System.in);
int userInput;
while(true) {
AskQuestion();
if (scanner.hasNextInt()) {
userInput = scanner.nextInt();
break;
}
scanner.next(); // consume non-int token
}
Another alternative which utilizes the Scanner#nextLine() method along with the String#matches() method and a small Regular Expression (RegEx) to ensure that the supplied string does indeed contain all numerical digits:
Scanner scanner = new Scanner(System.in);
String userInput = "";
int desiredINT = 0; // Default value.
while (desiredINT == 0) {
AskQuestion();
userInput = scanner.nextLine();
if (userInput.matches("\\d+")) {
desiredINT = Integer.parseInt(userInput);
if (desiredINT < 1 || desiredINT > 120) {
System.out.println("Invalid Input! The age supplied is not "
+ "likely! Enter a valid Age!");
desiredINT = 0;
}
}
else {
System.out.println("Invalid Input! You must supply an Integer "
+ "value! Try Again...");
}
}
System.out.println("Your age is: --> " + desiredINT);
And the AskQuestion() method:
private void AskQuestion() {
System.out.println("How old are you?");
}
This is nice and short one
Scanner scanner = new Scanner(System.in);
do askQuestion();
while(!scanner.nextLine().trim().matches("[\\d]+"));
Tell me if you like it
Note it just tell you if number was an int , and keeps repeating if not, but doesn't give you that int back , tell me if you need that, i shall find a way
My solution might be a bit bloated, but I hope it's nice and clear what's going on. Please do let me know how it can be simplified!
import java.util.Scanner; // Import the Scanner class
class Main {public static void main(String[] args) {
Scanner myObj = new Scanner(System.in); // Create a Scanner object
String unit;
// unit selector
while (true) {
System.out.println("Did you measure ion feet or meters? Type 'meters' or 'feet': ");
String isUnit = myObj.nextLine();
if (isUnit.equals("feet") || (isUnit.equals("meters"))) {
unit = isUnit;
break;
} else {
System.out.println("Please enter either 'meters' or 'feet'.");
}
}
System.out.println("Use selected " + unit);
}
Here is my code:
import java.util.*;
class Main {
public static void main(String[] args) {
Scanner Keyboard = new Scanner(System.in);
{
System.out.println("What is the answer to the following problem?");
Generator randomNum = new Generator();
int first = randomNum.num1();
int second = randomNum.num2();
int result = first + second;
System.out.println(first + " + " + second + " =");
int total = Keyboard.nextInt();
if (result != total) {
System.out.println("Sorry, wrong answer. The correct answer is " + result);
System.out.print("DO you to continue y/n: ");
} else {
System.out.println("That is correct!");
System.out.print("DO you to continue y/n: ");
}
}
}
}
I'm trying to keep the program to continue but if the user enters y and closes if he enters n.
I know that I should use a while loop but don't know where should I start the loop.
You can use a loop for example :
Scanner scan = new Scanner(System.in);
String condition;
do {
//...Your code
condition = scan.nextLine();
} while (condition.equalsIgnoreCase("Y"));
That is a good attempt. Just add a simple while loop and facilitate user input after you ask if they want to continue or not:
import java.util.*;
class Main
{
public static void main(String [] args)
{
//The boolean variable will store if program needs to continue.
boolean cont = true;
Scanner Keyboard = new Scanner(System.in);
// The while loop will keep the program running unless the boolean
// variable is changed to false.
while (cont) {
//Code
if (result != total) {
System.out.println("Sorry, wrong answer. The correct answer is " + result);
System.out.print("DO you to continue y/n: ");
// This gets the user input after the question posed above.
String choice = Keyboard.next();
// This sets the boolean variable to false so that program
// ends
if(choice.equalsIgnoreCase("n")){
cont = false;
}
} else {
System.out.println("That is correct!");
System.out.print("DO you to continue y/n: ");
// This gets the user input after the question posed above.
String choice = Keyboard.next();
// This sets the boolean variable to false so that program
// ends
if(choice.equalsIgnoreCase("n")){
cont = false;
}
}
}
}
}
You may also read up on other kinds to loop and try implementing this code in other ways: Control Flow Statements.
So I just started learning Java, its literally like my 1st day and I wanted to try to make a coinflip game. I already know a decent amount of Javascript and so i was trying to apply that knowledge to java. So everything has been working so far except one thing: Prompting a user for a choice. So read online that i have to import a scanner so i did that as you can see from my code. I also tried some code where you can have the user import a string but you can see a bit later in my program i change the variable userChoice into a number. So basically i just need help with this. If there is some way to have a variable type that can store both numbers or strings that would be best. But im tottaly open to other ways of doing this! Thanks in advanced! Here is the code:
package test;
import java.util.Scanner;
public class testclass {
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("hi");
int bob;
bob = (int) Math.floor(Math.random()*2);
System.out.println(bob);
System.out.println("Enter heads or tails?");
System.out.println("You entered "+ userChoice);
if (bob == 0) {
System.out.println("Computer flipped heads");
}
else {
System.out.println("Computer flipped tails");
}
if(userChoice == "Heads") {
userChoice = 0;
}
else {
userChoice = 1;
}
if (userChoice == bob) {
System.out.println("You win!");
}
else {
System.out.println("Sorry you lost!")
}
}
}
Use a scanner, as you said:
Scanner in = new Scanner(System.in);
Then, prompt the user to enter something in:
String userChoice = in.nextLine();
Also, when you compared strings:
if(userChoice == "Heads") {...
that's bad to do for none-primitive objects. It's best to only use the == to compare values that are ints or enums. If you compare a String like this, it won't work, because it's checking if the objects are the same. Instead, compare like this:
if(userChoice.equals("Heads")) {...
Also, to convert to an int (NOTE: You can't convert one type of object to another that aren't related in any way! You'll have to create a new object if you're wanting to do that), do this:
int myInt = Integer.parseInt(myString); // NOTE: Can throw NumberFormatException if non-number character is found.
So your program should look somewhat like:
package test;
import java.util.Scanner;
public class testclass {
public static void main(String[] args) {
//System.out.println("hi");
Scanner in = new Scanner(System.in);
int bob;
int userChoice;
String input;
bob = (int) Math.floor(Math.random()*2);
System.out.println(bob);
System.out.println("Enter heads or tails?");
input = in.nextLine(); // waits for user to press enter.
System.out.println("You entered "+ input);
if (bob == 0) {
System.out.println("Computer flipped heads");
}
else {
System.out.println("Computer flipped tails");
}
if(input.equals("Heads")) {
userChoice = 0;
}
else {
userChoice = 1;
}
if (userChoice == bob) {
System.out.println("You win!");
}
else {
System.out.println("Sorry you lost!");
}
in.close(); // IMPORTANT to prevent memory leaks
}
}
You've already imported the Scanner class so you can now create a variable of the type Scanner for taking inputs.
Scanner in = new Scanner();
userChoice = in.nextLine();
nextLine() can be used to input a character or a string from the user.
To convert the string into a integer, You can assign the integer value to the string in the following way.
if(userChoice == "Heads") {
userChoice = "" + 0;
}
else {
userChoice = "" + 1;
}
"String" datatype in Java can hold both numbers and strings (as you asked). You can get user input using Scanner utility as below:
Scanner input = new Scanner();
userChoice = input.nextLine(); // if it is a string
//userChoice = input.nextInt(); // if it's integer choice
If your string is an integer then you can also parse it to get its integer value. For parsing:
int value = Integer.parseInt(userChoice);
Also for comparing String values you should use "equals" function rather than "==".
if(userChoice.equals("Heads")){...} //rather than if(userChoice == "Heads"){...}
Having imported java.util.Scanner, to get input from the user as a String, create a Scanner object that parameterizes System.in and assign userChoice the value of nextLine() invoked by the Scanner object:
Scanner input = new Scanner(System.in);
String userChoice = input.nextLine();
A few things about your code. The relational operator, ==, is used for comparing primitive data - not objects. Use string1.equals(string2) to see if two strings are equal.
Also, bob = (int) Math.floor(Math.random()*2); is really bob = (int)(Math.random() * 2);
because casting a double as an integer truncates the double to the highest integer less than or equal to it.
It might help you to get the ideas.
public static void main(String[] args) {
Random rd = new Random();
//Enter 1 0R 0
int bob = rd.nextInt(2);
String userChoice;
Scanner sc = new Scanner(System.in);
System.out.println("Please enter a number");
userChoice = sc.nextLine();
System.out.println("You entered " + userChoice + " and bob is " + bob);
int uc = Integer.parseInt(userChoice);
if (uc == bob) {
System.out.println("Hehe");
} else {
System.out.println("Sorry");
}
}