I've been messing around with this code for about an hour now trying to make it loop if the user inputs a character instead of a number
System.out.println("Enter level student last completed (0-3): ");
int level = in.nextInt();
while (level > 3 || level < 0){
System.out.println("Please enter a valid level!: ");
level = in.nextInt();
}
I thought of adding !in.hasNextInt()
to the line while (level > 3 || level < 0)
to make it
while (!in.hasNextInt() || level > 3 || level < 0)
but this doesn't help as the programme still crashes if a character is input.
edit:
System.out.println("Enter level student last completed (0-3): ");
int level = 1; //in.nextInt();
while (in.hasNextInt()==false || level > 3 || level < 0){
in.next();
System.out.println("Please enter a valid level!: ");
}
level = in.nextInt();
You can create a while loop to repeatedly ask for an input until it gets the kind it likes
int i;
while(scan.hasNextInt()==false){ //keep asking until it gets something it likes
scan.next(); //<--consume bad input, important!
System.out.println("Only integers are valid");
}
i=scan.nextInt();
System.out.println(i);
You can package this up into method which will make life easier when we want to incorporate more logic
public static int getSafeInteger(){
Scanner scan=new Scanner(System.in); //if using scanner over and over consider passing the scanner as an argument
while(scan.hasNextInt()==false){
scan.next();
System.out.println("Only integers are valid");
}
return scan.nextInt();
}
Then we can use that method within your existing loop
System.out.println("Enter level");
Scanner scan=new Scanner(System.in);
int level=getSafeInteger();
while (level > 3 || level < 0){
System.out.println("Please enter a valid level!: ");
level = getSafeInteger();
}
使用nextLine()
并尝试使用Integer.parseInt(String)
其解析为整数。
You could do something like this:
int level;
while (true) {
if (in.hasNextInt()) {
// now we know at least the input is a number
if (level > 3 || level < 0) {
// aww, it's an invalid number :(
in.nextLine(); // clear bad input
System.out.println("Please enter a valid level (0-3)!: ");
} else {
// hooray! store the input now
level = in.nextInt();
break; // out of the infinite loop
}
} else {
// input is not a number
in.nextLine(); // clear bad input
System.out.println("Please enter a number!: ");
}
}
Try this:
Scanner sc = new Scanner(System.in);
int level;
System.out.printf("Enter level student last completed (0-3): ");
while(true) {
try {
level = Integer.parseInt(sc.next());
if (level < 4 && level > -1) {
break;
}
} catch (Exception ex) { }
System.out.printf("Please enter a valid level!: ");
}
you can set default value of level more than 3 and do following
do
{
System.out.println("Enter level student last completed (0-3): ");
try{
level = in.nextInt();
}catch(InputMismatchException e){
System.out.println("Not a valid Number");
in.nextLine();
}
}while (level > 3 || level < 0);
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