Getting User input with Scanner
I am trying to have a scanner take input in a loop. Once the user wants to finish he can exit this loop. I have tried many different ways to do it but there is always some problem. This is the code:
private void inputEntries() {
Scanner sc = new Scanner(System.in);
System.out.println("Continue?[Y/N]");
while (sc.hasNext() && (sc.nextLine().equalsIgnoreCase("y"))) {//change here
System.out.println("Enter first name");
String name = sc.nextLine();
System.out.println("Enter surname");
String surname = sc.nextLine();
System.out.println("Enter number");
int number = sc.nextInt();
Student student = new Student(name, surname, number);
students.add(student);
try {
addToFile(student);
} catch (Exception ex) {
Logger.getLogger(TextReader.class.getName()).log(Level.SEVERE, null, ex);
}
System.out.println("Continue?[Y/N]");
}
}
The problem with the code above, which also happens on different methods I tried, is that when the user types Y, the Scanner
will skip the first input for first name,and jump to the surname. If the user types N the loop stops correctly. Someone can explain the reason this happens, and how to overcome using Scanner
class?
p.s: Doing something like while(sc.nextLine().equals("Y"))
, will cause the loop to terminate before getting input from user after first run of the loop.
Solution 1:
This is because you are using Scanner#next
method. And if you look at the documentation of that method, it returns the next token read.
So, when you read user input using next
method, it does not read the newline
at the end. Which is then read by the nextLine()
inside the while
loop. And thus, your firstName
contains a newline
without you knowing.
So, you should use nextLine()
in your while rather than next()
.
Similar is the case with nextInt
method. It also does not read the newline. So, you can read
using readLine
and convert it to int
using Integer.parseInt
. It can throw NumberFormatException
if input value cannot be converted to int
. So you need to handle it accordingly.
You can try the below code: -
Scanner sc = new Scanner(System.in);
System.out.println("Continue?[Y/N]");
while (sc.hasNext() && (sc.nextLine().equalsIgnoreCase("y"))) {//change here
System.out.println("Enter first name");
String name = sc.nextLine();
System.out.println("Enter surname");
String surname = sc.nextLine();
System.out.println("Enter number");
int number = 0;
try {
number = Integer.parseInt(sc.nextLine());
} catch (IllegalArgumentException e) {
e.printStackTrace();
}
System.out.println("Continue?[Y/N]");
}
But, note one thing, if you enter a value that cannot be passed to Integer.parseInt
you will get an exception, and that input will be skipped. For that case, you need to handle it by using while
loop.
Or, if you don't want to do that exception handling: -
You can add an empty sc.nextLine()
after sc.nextInt()
, that will consume the newline
left over, like this: -
// Left over part of your while loop
String surname = sc.nextLine();
System.out.println("Enter number");
int number = sc.nextInt();
sc.nextLine(); // To consume the left over newline;
System.out.println("Continue?[Y/N]");
Solution 2:
- Use
equalsIgnoreCase(..)
to prevent the case of Y or N being lower case and vice versa. - Don't use
sc.next()
rathersc.nextLine()
to achieve what you want, becausenext()
only reads up to the next space whilenextLine()
reads up to the next\n
break. - Don't use
nextInt()
read all data asString
and then convert becausenextInt()
is likenext()
thus is does not read up to the next \n.
Try it like this:
Scanner sc = new Scanner(System.in);
System.out.println("Continue?[Y/N]");
while (sc.hasNext() && (sc.nextLine().equalsIgnoreCase("y"))) {//change here
System.out.println("Enter first name");
String name = sc.nextLine();
System.out.println("Enter surname");
String surname = sc.nextLine();
System.out.println("Enter number");
int number=0;
try {
number = Integer.parseInt(sc.nextLine());//read int as string using nextLine() and parse
}catch(NumberFormatException nfe) {
nfe.printStackTrace();
}
System.out.println("Continue?[Y/N]");
}