Java String Input error - java

So this question is kinda simple, but I was wondering why the following code, after running perfectly the first time, jumps straight to "Enter the page number: ", instead of asking for the title the second loop around. I've read somewhere that there is something up with Java that won't allow for a reuse of a Scanner. Is this the problem that I'm facing? I've tried to use kbReader.next() and that works, but the code only works with strings without spaces.
String title = "";
int page = 0;
int i = 0;
Scanner kbReader = new Scanner(System.in);
for (i=1;i<=3;i++){
System.out.print("Enter the title: ");
title = kbReader.nextLine();
System.out.print("Enter the page number: ");
page = kbReader.nextInt();
System.out.print(title);
System.out.println(page);
}
Much help appreciated!

You should add a kbReader.nextLine(); after kbReader.nextInt();. On the second loop, your kbReader.nextInt(); is just reading the end-of-line in the stream, left out by kbReader.nextInt();.

Related

Strange output when I read from scanner

I'm trying to create a videoStore with the basic CRUD operation. For creating each movie I need to read the title, the year and the gender as below:
System.out.print("name: ");
name = in.nextLine();
System.out.print("year: ");
year = in.nextInt();
in.nextLine();
System.out.print("gender: ");
gender = in.next();
When I enter the addMovie option, I get this print on the console
(name: year:)
Can someone explain to me why it happens as above?
Here is the rest of the method:
static ArrayList<Movie> movies = new ArrayList<Movie>();
static Scanner in = new Scanner(System.in);
public static void InserirFilme() {
String name;
int year;
String gender;
boolean existe = false;
System.out.print("name: ");
name = in.nextLine();
System.out.print("year: ");
year = in.nextInt();
in.nextLine();
System.out.print("gender: ");
gender = in.next();
Movie movie = new Movie(name, year, gender);
for(Movie m: movies)
{
if(movie == m)
{
existe = true;
}
}
if(!existe)
{
movies.add(movie);
}
else
{
System.out.println("the movie already exists in the videoStore");
}
}
Calling next does not remove the line break, which means the next time you call InserirFilme the call to read the name can complete immediately. Use nextLine.
System.out.print("gender: ");
gender = in.nextLine();
(You probably mean "genre" instead of "gender" though)
Also, as mentioned in the comments, this check will never succeed:
if(movie == f)
You run this method in loop (right?)
The first call reads input correctly, but it leaves the linebreak in System.in after the last in.next().
On next call the name: is printed, then scanner reads an empty string from System.in because the linebreak already exists here.
And after thet the year: is printed on the same line because no new linebreaks are entered.
So you just have to insert another in.nextLine() after reading gender (or genre :) )
Or use nextLine() for read genre instead of next(), because genre might have more than one word.
But there are some disadvantages with using fake nextLine() to 'eat' linebreak - there might be another text which you doesn't process. It's a bad practice - to loose the data user entered.
It is better to read all the data from line, then validate/parse it, check isn't there some extra data, and if the data is invalid show notification and let him try to enter the right value.
Here are some examples how to deal with user input manually - https://stackoverflow.com/a/3059367/1916536. This is helpful to teach yourself.
Try to generalize user input operations:
name = validatedReader.readPhrase("name: ");
year = validatedReader.readNumber("year: ");
genre = validatedReader.readWord("genre: ");
where ValidatedReader is a custom wrapper for Scanner which could use your own validation rules, and could gently re-ask user after a wrong input.
It could also validate dates, phone numbers, emails, url's or so
For production purposes, it is better to use validation frameworks with configurable validation rules. There are a lot of validation frameworks for different purposes - Web, UI, REST etc...
when i enter the addMovie option, i get this print on the console (name: year:) can someone explain me why it happens i already searched a lot and i cant understand why :S
The way i understood your question is that you are getting the output (name: year: ) in a line and want it in seperate lines? In that case you simply can use System.out.println(String); instead of System.out.print(String). On the other hand you can also use "\n" whenever you want a linebreak within a String. Hope i could help you :).
Edit: If this was not an answer to your question, feel free to tell me and clarify your question :)
For String name you are using in.nextLine(); i.e the data entered on the entire line will be added to name string.
After "name: " is displayed, enter some text and press enter key, so that the year and gender fields will get correct values.
The code written is correct but you are not giving appropriate input through the scanner.
I recommend to use
String name = in.next();//instead of String name = in.nextLine();
You may instantiate Scanner Class differently for String and Integer type input. It works for me :)
Example:
static Scanner in1 = new Scanner(System.in);
static Scanner in2 = new Scanner(System.in);
Please use nextLine() for 'name' and 'gender'. It may contain more than one word. Let me know if it works.
Example:
System.out.print("name: ");
name = in1.nextLine();
System.out.print("year: ");
year = in2.nextInt();
System.out.print("gender: ");
gender = in1.nextLine();

Java Scanner doesn't work in Processing

For an assignment I have due, my group and I were asked to code an educational/interactive game, and we decided on a basic maths one.
To get the users answers, we decided to use Java Scanner and put this line of code at the top of all the code we have;
java.util.Scanner
One of the loops that use this is the page with the questions on it, the loop looking something like this;
scoreCount = 0;
for (questions = 0; questions < 5;) {
//get the user's answer
userAnswer[questions] = input.nextInt();
//text box for users answer
if (userAnswer[questions] == compAnswer) {
//put tick next to answer
//add one to score
scoreCount = scoreCount + 1;
} else if (userAnswer[questions] != compAnswer) {
//put cross next to answer
}
//go to next question
questions++ ;
}
I'm working through all the errors that were thrown up and every time i don't have java.util.Scanner commented out Processing throws us the errors unexpected token: and then either class or void, which i don't get, but when java.util.Scanner is commented out, the classes and voids all work and the .input.nextInt() isn't recognised.
I am new to Java programming and Processing, any help at all would be greatly appreciated
EDIT
i think this is the link which lets you see my code, it's called Test;
https://github.com/MeganSime/Week8DataVis
you have to check if scanner has next int (token)
Scanner input = new Scanner(System.in);
.
.
if(input.hasNextInt()) { // or hasNext()
userAnswer[questions] = input.nextInt();
}
You're probably inserting a non int value where the scanner expects that. You should do something like that:
if(input.hasNextInt()) {
userAnswer[questions] = input.nextInt();
} else {
scan.next(); //consume any non-int value like ":"
}

Java is skipping a line (Strings in a Scanner ??) [duplicate]

This question already exists:
Scanner issue when using nextLine after nextXXX [duplicate]
Closed 9 years ago.
I am learning Java, and I'm not very far into it, and I don't know why but Java seemed to skip a line. I don't think the code from all my pages is really neccesery so I will just put the first page and the result I get when using it. Thanks!
import java.util.Scanner;
public class First {
public static void main(String args[]){
Scanner scanz = new Scanner(System.in);
System.out.println("Hello, please tell me your birthday!");
System.out.print("Day: ");
int dayz = scanz.nextInt();
System.out.print("Month: ");
int monthz = scanz.nextInt();
System.out.print("Year: ");
int yearz = scanz.nextInt();
System.out.println("Now, tell me your name!");
System.out.print("Name: ");
String namez = scanz.nextLine();
Time timeObject = new Time(dayz,monthz,yearz);
Second secondObject = new Second(namez,timeObject);
System.out.println("\n\n\n\n\n" + secondObject);
}
}
It skips the line
String namez = scanz.nextLine();
Console output: (excuse the birthday bit, it is other stuff)
Hello, please tell me your birthday!
Day: 34
Month: 234
Year: 43
Now, tell me your name!
Name:
My name is and my birthday is 00/00/43
It doesn't give you a chance to give a name, it just skips straight past and takes the name as null. Please, if anyone could, tell me why! I want to learn Java, and this little annoyance is standing in my way.
Thanks!
The problem is that the nextLine gets any characters on the line, and the \n (newline character) is left over from the scanner inputs above.
So instead of letting you enter something new, it takes the \n as the input and continues.
To fix, just put two scanners back to back like this:
System.out.print("Name: ");
scanz.nextLine();
String namez = scanz.nextLine();
Just using:
String namez = scanz.next();
will work too, but will limit the names to be one word. (aka first name only)
I believe the intended use of nextLine is correct. The problem however is that nextInt does not create a newline token, and it's instead reading the rest of that line (which is empty). I believe that if another nextLine statement would be added after that, the code would work. Next on the other hand only recognizes the first word so that might not be the correct solution.

Getting accurate int and String input

I am having trouble reading in strings from the user after reading in an int. Essentially I have to get an int from the user and then several strings. I can successfully get the user's int. However, when I begin asking for strings (author, subject, etc...), my scanner "skips" over the first string input.
For example, my output looks like this:
Enter your choice:
2
Enter author:
Enter subject:
subject
As you can see, the user is never able to enter the author, and my scanner stores null into the author string.
Here is the code that produces the above output:
String author;
String subject;
int choice;
Scanner input = new Scanner(System.in);
System.out.println("Enter choice:");
choice = input.nextInt();
System.out.println("Enter author:");
author = input.nextLine();
System.out.println("Enter subject:");
subject = input.nextLine();
Any help would be greatly appreciated. Thank you!
-Preston Donovan
The problem is that when you use readLine it reads from the last read token to the end of the current line containing that token. It does not automatically move to the next line and then read the entire line.
Either use readLine consistently and parse the strings to integers where appropriate, or add an extra call to readLine:
System.out.println("Enter choice:");
choice = input.nextInt();
input.nextLine(); // Discard the rest of the line.
System.out.println("Enter author:");
author = input.nextLine();
This works perfectly.
Although while making previous programs like the one below it was not required. Can anyone explain this?
import java.util.Scanner;
public class Average Marks {
public static void main(String[] args) {
Scanner s = new Scanner ( System.in);
System.out.print("Enter your name: ");
String name=s.next();
System.out.print("Enter marks in three subjects: ");
int marks1=s.nextInt();
int marks2=s.nextInt();
int marks3=s.nextInt();
double average = ( marks1+marks2+marks3)/3.0;
System.out.println("\nName: "+name);
System.out.println("Average: "+average);

Java Scanner class reading strings [duplicate]

This question already has answers here:
Java Scanner class reading strings
(5 answers)
Closed 8 years ago.
I got the following code:
int nnames;
String names[];
System.out.print("How many names are you going to save: ");
Scanner in = new Scanner(System.in);
nnames = in.nextInt();
names = new String[nnames];
for (int i = 0; i < names.length; i++){
System.out.print("Type a name: ");
names[i] = in.next();
}
System.out.println(names[0]);
When I run this code, the scanner will only pick up the first name and not the last name. And it will sometimes skip a line when trying to enter a name, it will show up as if I had left the name blank and skip to the next name. I don't know what's causing this.
I hope someone can help me!
EDIT: I have tried in.nextLine(); it fixes the complete names but it still keeps a line, here is an example of the output:
How many names are you going to save: 3
Type a name: Type a name: John Doe
Type a name: John Lennon
Instead of:
in.next();
Use:
in.nextLine();
nextLine() reads the characters until it finds a new line character '\n'
After your initial nextInt(), there's still an empty newline in your input. So just add a nextLine() after your nextInt(), and then go into your loop:
...
Scanner in = new Scanner(System.in);
nnames = in.nextInt();
in.nextLine(); // gets rid of the newline after number-of-names
names = new String[nnames];
for (int i = 0; i < names.length; i++){
System.out.print("Type a name: ");
names[i] = in.nextLine();
}
...
Scanner.next stops reading when it encounters a delimiter, which is a whitespace. Use the nextLine method instead.
Try using:
System.out.println()
Instead of:
System.out.print()

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