public void enroll() {
Scanner in = new Scanner(System.in);
System.out.println("Enter course to enroll (Q to quit)");
while(!in.nextLine().equals("Q")) {
courses.add(in.nextLine());
}
}
The program should accept user input and add it to the ArrayList courses until the user enters "Q" but instead what's happening is that it seems like it's only registering and adding every other input. It's also adding the Q which is an issue.
Your code doesn't do what you want it to do.
How it should be: users inputs are processed one per iteration and if it's 'Q', then quit while.
How it actually is: users inputs are processed two per iteration(because you cal in.nextLine() both in conditional part and in body of while), and if first is not 'Q' then add second to list.
Here is my code to this:
Scanner in = new Scanner(System.in);
System.out.println("Enter course to enroll (Q to quit)");
String line;
while(!(line = in.nextLine()).equals("Q")) {
courses.add(line);
}
Your issue is that you are getting the next line twice, firstly inside the loop condition while(!in.nextLine().equals("Q")) { then again inside the loop courses.add(in.nextLine());.
One solution could be to use a string variable to store the line, and an if check to see if the condition is met:
public void enroll() {
Scanner in = new Scanner(System.in);
System.out.println("Enter course to enroll (Q to quit)");
String line = "";
while(true) {
//We should only get the next line once per loop:
line = in.nextLine();
//Now we can use the line
if (line.equals("Q")){
break;
}
courses.add(line);
}
}
Related
I've been trying to make a while loop where I enter in a movie number until the user types 'q' for quit, but every time I enter a valid number, I have to enter it twice before it prompts me with the "Enter movie number" message again. And the break function doesn't work when I wish to leave the loop. I simply wish to enter in the movie number once and break out when I want to.
public class Main {
public static void main(String[] args) {
while(true)
{
System.out.println("Enter in movie number: ");
Scanner input = new Scanner(System.in);
if(!input.hasNextInt())
{
System.out.println("invalid input");
continue;
}
if (Integer.parseInt(input.next()) < 0)
{
System.out.println("invalid no negative numbers");
continue;
}
if(Objects.equals(input.next(), "q"))
break;
}
}
I tried other variations of the while loop, but a similar thing has happened.
I assume your intention is to get one line of input, and if it is a number, process it somehow, and if not check if the user wants to quit.
You've got a couple problems with your program, firstly, you're creating a new Scanner within the while loop, which creates unnecessary overhead. Second, you're trying to get 2 lines of input within your loop, you wait for the user to input an integer, then you try to parse that integer with input.next(). Afterwards, you call input.next() again to check if the user wants to quit. By calling next() twice, you're requiring the user to input 2 lines, causing the issue you were describing.
You can fix this by calling next() once and storing its return value in a variable, then check if it equals q for quit, otherwise you can parse an integer value from it.
Here is working code that applies fixes to these issues:
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while(true) {
System.out.println("Enter in a movie number:");
// Get user input
String input = scanner.next();
// If the input equals q, we break out of the loop
if(input.equalsIgnoreCase("q")) break;
int intInput;
try {
// Get integer input
intInput = Integer.parseInt(input);
} catch(NumberFormatException e) { // Input was not a number
System.out.println("Invalid, must input a number");
continue;
}
if(intInput < 0) {
System.out.println("Invalid, no negative numbers");
continue;
}
}
}
}
Also, a small note, instead of using Object.equals to check if two strings are equal you can just use the equals method inside of the String class like so: str1.equals(str2).
public static void main(String[] args) {
List<String> arrayList = new ArrayList<>();
Scanner input = new Scanner(System.in);
do {
System.out.println("Enter a product");
String product = input.nextLine();
arrayList.add(product);
}
while (!input.nextLine().equalsIgnoreCase("q"));
System.out.println("You wrote the following products \n");
for (String naam : arrayList) {
System.out.println(naam);
}
}
I'm trying to get some input from the user and store them into arraylist. The problem is I have to write the item twice to add an item into the list. I can't figure out why!
Instead of do-while loop use only while
while (true){
System.out.println("Enter a product");
String product = input.nextLine();
if (!product.equalsIgnoreCase("q"))
arrayList.add(product);
else
break;
}
Every time you write readLine(), a line is read. In this loop,
do {
System.out.println("Enter a product");
String product = input.nextLine();
arrayList.add(product);
}
while (!input.nextLine().equalsIgnoreCase("q"));
There are two occurrences of readLine(), so two lines are read every iteration. The first line is always added to the list and not checked against q, and the second is never added to the list, and always checked against q.
You should only do nextLine once:
while (true) {
System.out.println("Enter a product");
String product = input.nextLine(); // only this one time!
if (!product.equalsIgnoreCase("q")) {
arrayList.add(product);
} else {
break;
}
}
It happenes coz input.nextLine() makes java read the input. You should read the line and only then do the stuff:
Scanner input = new Scanner(System.in);
String product = input.nextLine();
System.out.println("Enter a product");
while (!product.equalsIgnoreCase("q")) {
arrayList.add(product);
System.out.println("Enter a product");
product = input.nextLine();
}
You can read the String values using input.next() once and have a while loop in place and read further values into your list only if the value is not equal to q.
If you have read it twice as in your case, one value is added to the list in your do part, and the value you read again in your while part is only compared to q and so to exit your code, you will be missing one value and adding another and have to give two q values one after another to exit it.
Also, since most of the other users have given there answers with nextLine instead of next you may want to check what next does and what nextLine does. In brief, if you enter names of products separated by a delimiter (default space), then with next, each value separated by the space is considered a product. Similarly, if you enter on different line as well. But, with nextLine, each line as a whole will be added as a new product. It depends on how you may want to achieve this as per your requirement.
public static void main(String[] args) {
List<String> arrayList = new ArrayList<>();
Scanner input = new Scanner(System.in);
String product = input.next();
while(!product.equalsIgnoreCase("q")) {
arrayList.add(product);
product = input.next();
}
System.out.println("You wrote the following products \n");
for (String naam : arrayList) {
System.out.println(naam);
}
}
My program seems stuck in the middle of my while loop, without crashing and without looping infinitely. It just stops.
The loop runs for as many input as the user provides, but then does not move on the the next line of code.
It is my first time using the hasNextDouble() in java. Am I doing it right?
Here is the while loop in question:
System.out.print("Grades (separated by a space)");
while(in.hasNextDouble())
{
student1.addGrade(in.nextDouble());
}
And here is a little bit more of my code:
Scanner in = new Scanner(System.in);
String input = "";
Student student1 = new Student();
GradeBook book = new GradeBook();
// Sets the name of the first student
System.out.print("Name: ");
input = in.nextLine();
student1.setNames(input);
// Sets the grades of the first student
System.out.print("Grades (separated by a space)");
while(in.hasNextDouble()){
student1.addGrade(in.nextDouble());
}
// Put the student into the GradeBook
book.addStudent(student1);
// Prints the report
System.out.print(book.reportGrades());
You state you want space separated input, in a single line. I would suggest taking the input as a String, and then splitting it up, like
Scanner in = new Scanner(System.in);
String line = in.nextLine();
for(String s : line.split(" ")){
student1.addGrade(Double.parseDouble(s)); //gives exception if value is not double
}
Scanner.hasNextDouble will continue to return true, until you enter a non-Double value.
With hasNext() you check if there is anything, then with hasNextDouble() check if the next input can be cast to double. You read the value with next(), but the value is still a string, so you need to parse it to double.
Also, you need a way to get out of the loop with break when input is no longer a number.
while (in.hasNext()) {
if (in.hasNextDouble()) {
student1.add(Double.parseDouble(in.next()));
} else {
break;
}
}
I am having a little problem with my code. Compiling and running works well, however, when I attempt to break out of the inner loop,
System.out.println("Type which category you want to add to.");
System.out.println("Homework, Classwork, Labs, Test, Quizzes, Midterm, Final");
The code above is printing twice to the terminal when I only want it to print once.
I have a feeling that is a simple mistake with the way my brackets are aligned but I am having difficulty with figuring out how to do it. Any help would be greatly appreciated!
import java.util.Scanner;
public class GetGrade {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
final int MAX = 15;
int[] homework = new int[MAX];
int[] classwork = new int[MAX];
int[] lab = new int[MAX];
int[] test = new int[MAX];
int[] quizzes = new int[MAX];
int[] midterm = new int[MAX];
int[] fin = new int[MAX];
int hwCount, clCount, labCount, testCount, quizCount, midCount, finCount;
double hwTotal, clTotal, labTotal, testTotal, quizTotal, midTotal, finTotal;
double grade = 0;
String selection = "";
System.out.println();
System.out.println("Welcome to GetGrade!");
System.out.println();
while (true) {
System.out.println("Type which category you want to add to.");
System.out.println("Homework, Classwork, Labs, Test, Quizzes, Midterm, Final");
selection = input.nextLine();
if (selection.equals("homework")) {
System.out.print("What percentange of your grade is homework? > ");
double hwPercent = input.nextDouble();
System.out.println("Now begin typing your grades. When you are finished, type -1.");
for (int i = 0; i < homework.length; i++) {
homework[i] = input.nextInt();
hwTotal = homework[i] * hwPercent;
grade += hwTotal;
if (homework[i] == -1) break;
}
}
}
}
}
It's just as trivial as it seems:
The call to input.nextInt(); in your inner loop does not include the newline.
So you are breaking of the innerloop, receiving the next line which only contains the newline - character in input.nextLine(); which is the remaining input of your "-1\n" line and proceed with the main loop again as it does not match "homework".
Try setting the conditional variable in your while loop to an actual boolean rather than true.
Also, when you invoke "break", you are only breaking out of the for loop. If you reassign a boolean variable to false at this point, you would exit the while loop completely.
Just before while loop ends, add a "Do you want to continue? (Y/N)" functionality.
If user enters "N" or anything else, execute another break. And that break will make you get out of the while loop.
The simple way to get your code working is to change
selection = input.nextLine();
to
selection = input.next();
next() only reads in a string value (which is what you are actually doing in your code) instead of the newline character as Peter has suggested.
So the an extra iteration of the while does not take place when you read the newline character.
When you use a scanner to read a line from the keyboard, it reads everything up to and including the newline character the user types to submit their input. So for example:
Type which category you want to add to.
Homework, Classwork, Labs, Test, Quizzes, Midterm, Final
>
If you type "homework" and then ENTER, the actual input becomes "homework\n". input.nextLine() will scan the input until it encounters the first newline character, '\n', which it will consume and then it returns everything up to that point (i.e. "homework").
Your problem here is that input.nextInt() does NOT consume a newline character, and so there is still a newline character in the input buffer by the time your while loop starts another round.
Now begin typing your grades. When you are finished, type -1.
> ...
> -1
=> User input is "-1\n"
-------------------------------
// Meanwhile, back in the code...
for (int i=0;i<homework.length;i++) {
homework[i] = input.nextInt(); // <--- This call consumes "-1" but leaves '\n'
hwTotal = homework[i] * hwPercent;
grade += hwTotal;
if (homework[i] == -1) break;
}
That newline is consumed by the next call to input.nextLine(), leaving the input buffer empty.
while (true) {
System.out.println("Type which category you want to add to.");
System.out.println("Homework, Classwork, Labs, Test, Quizzes, Midterm, Final");
selection = input.nextLine(); // <--- This call consumes the leftover '\n' and returns the empty string
...
And because "" is not equal to "homework", the while loop goes around one more time, but this time the input buffer is empty, and so the call to input.nextLine() behaves as you would expect.
// selection is empty, so this condition fails and the program loops back around
if (selection.equals("homework")) {
...
There are two easy solutions to this problem. You can
Use Integer.parseInt(input.nextLine()) instead of input.nextInt()
Add an extra call to input.nextLine() at the end of your while loop to consume the final newline character
The first option is probably the most robust, and you get the added benefit of a run-time error being thrown if they do not give you a valid integer as input.
I am currently using a Scanner to record the user input which is a String and print it out. If the user input is a single name such as Alan, it works fine. If I enter a name with spacing such as Alan Smith, it returns an error saying InputMisMatchException.
I read around similar cases here and they advised to use nextLine() instead of next(). It made sense but that doesn't work for me either. When I use a nextLine(), it immediately skips the step where I enter the name and goes back to the starting of the loop asking me to input choice again. Please advice how I can correct this. Thank you.
import java.io.IOException;
import java.util.Scanner;
public class ScannerTest {
static String name;
static Scanner in = new Scanner(System.in);
static int choice;
public static void main(String[] args) {
while(choice != 5){
System.out.print("\nEnter Choice :> ");
choice = in.nextInt();
if(choice == 1){
try{
printName();
}
catch(IOException e){
System.out.println("IO Exception");
}
}
}
}
private static void printName()throws IOException{
System.out.print("\nEnter name :> ");
name = in.next();
//name = in.nextLine();
if (name != null){
System.out.println(name);
}
}
}
Try this instead: add name = in.nextLine(); after choice = in.nextInt();.
Then try replacing name = in.next(); with name = in.nextLine();
Explanation: After the scanner calls nextInt() it gets the first value and leaves the rest of the string to the \n. We then consume the rest of the string with nextLine().
The second nextLine() is then used to get your string parameters.
The problem is easy: when you prompt the user to enter his/her choice, the choice will be an int followed by a new line (the user will press enter). When you use in.nextInt() to retrieve the choice, only the number will be consumed, the new line will still be in the buffer, and, so, when you call in.nextLine(), you will get whatever is between the number and the new line (usually nothing).
What you have to do, is call in.nextLine() just after reading the number to empty the buffer:
choice = in.nextInt();
if (in.hasNextLine())
in.nextLine();
before to call name = in.next(); do this in = new Scanner(System.in);
the object need rebuild itself because already has value.
good luck