We Keep Coding

Issue with Reading two Int values from a file

I have file with the below data
A,8,43
B,7,42,
C,9,34
I am using the below code to read the data
Scanner input = new Scanner(new File("D:\\test.txt"));
input.useDelimiter(",|\n");
while(input.hasNext()) {
String name = input.next();
int age = input.nextInt();
int height = input.nextInt();
When I am executing the program I am getting InputMisMatch exception,
Please suggest what is mistake.

At end of second line you have , and line separator (I am assuming \n) This means you have empty element between these two delimiters.
So in third iteration
String name = input.next();
int age = input.nextInt();
int height = input.nextInt();
input.next(); is consuming "", which means input.nextInt() will try to consume C.
To solve this problem you can set delimiter to be combination of one or more commas and line separators like
input.useDelimiter("(,|\n)+");
To improve your code even farther instead of \n you can use \\R added in Java 8 (or \r|\n in earlier versions) to handle all line separators, because currently you don't consider \r as delimiter so it can be treated as valid token.
So better solution would be using
input.useDelimiter("(,|\\R)+"); //for readability
or even
input.useDelimiter("[,\r\n]+");

The problem lies at the use of the useDelimiter method. This method accepts a regular expression as a parameter. You can't just say ,|\n to mean "comma or new line". There are rules.
What you should pass in is "[,\\n]+". This means "one or more characters in the following set: [comma, new line character]".
With the regex that you are passing currently, ,|\n, it means that the delimiter should be either , or \n, but not both. So when it encounters the second line:
B,7,42,
this is what happens:
next reads "B"
nextInt reads "7"
nextInt reads "42"
next reads an empty string that is between the "," and the new line.
nextInt now tries to read the next token "C", which it can't.
EXCEPTION!

I would do things differently -- use one Scanner to parse each line of the File and use a 2nd Scanner nested within the while loop to extract tokens or data from the lines obtained from the first Scanner. For example:
String filePath = "D:\\test.txt";
File file = new File(filePath);
// use try-with-resources
try (Scanner input = new Scanner(file)) {
while (input.hasNextLine()) {
String line = input.nextLine();
Scanner lineScanner = new Scanner(line);
lineScanner.useDelimiter("\\s*,\\s*"); // get comma and any surrounding whitespace if present
String name = "";
int age = 0;
int height = 0;
if (lineScanner.hasNext()) {
name = lineScanner.next();
} // else ... throw exception?
if (lineScanner.hasNextInt()) {
age = lineScanner.nextInt();
} // else ... throw exception?
if (lineScanner.hasNextInt()) {
height = lineScanner.nextInt();
} // else ... throw exception?
// use name, age, height here
System.out.printf("%s %s %s%n", name, age, height);
lineScanner.close(); // don't waste resources -- return them
}
} catch (IOException e) {
e.printStackTrace();
}

Removing Spaces from Scanner (System.in) Input

Right now I'm working on taking an equation, in "infix" notation and remove any spaces within that string prior to performing the rest of my program. Right now, without any spaces in the string, I receive the correct "Postfix" equation in return. But for some reason I can't seem to remove the spaces of a string that was entered using new Scanner(System.in); prior to performing my "Postfix" method(s). Here is the main method of my file:
public static void main(String[] args){
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter the equation you'd like to evaluate: ");
InfixToPostFix postFixString = new InfixToPostFix();
String infix = keyboard.next();
String newInfix = infix;
//String newInfix = "9 * 5.3";
//String deleteSpaceInInfix = newInfix.replace(" ", "");
//System.out.println("deleteSpaceInInfix: " + deleteSpaceInInfix);
System.out.println("Postfix representation: " + postFixString.InfixToPostfix(infix));
}
Now I've noted out three lines that I tried to test while noting out the lines using the scanner information. In doing so, the result of the lines commented out is: 9*5.3 as expected. So I believe that it is something with the Scanner String object.
The way that you see this method now, when 9 * 5.3 is entered produces only 9. Everything after the first space is dropped.
I've tried to look up possible causes for this problem I'm not understanding and looked it up in the API documentation but haven't seen anything.
I'd appreciate any information in helping me better understand why my Scanner object (String infix = keyboard.next(); in this instance) is being treated differently than a normal String newInfix = "9 * 5.3; object is?

The default delimiter of Scanner is whitespace. Use nextLine() if you want to read an entire line:
Scanner keyboard = new Scanner(System.in);
String infix = keyboard.nextLine();
infix = infix.replace(" ", "");
System.out.println(infix);
Note: There's also hasNextLine() to check if there is another line in the input.

Replace the whole line in the text document with the word at the end of the line

I am trying to replace the line with the word at the end of the line. Standing with the current I am getting the same line.
Simple:
apple - water- wall - street- light- book
REsult should be
book
Code:
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
if (line.contains("-") ) {
String[] lineSplitted = line.split("-");
int index = lineSplitted.length - 1;
String direction = lineSplitted[index];
line.replace(line, direction);
}
}

If what you are trying to accomplish is an input line which is replaced with the last word in that line, you could simply change your code to the following:
Scanner scanner = new Scanner(System.in);
String line = scanner.nextLine();
String[] parts = line.split("\\s");
line = parts[parts.length-1];

The type String is immutable, meaning that once constructed, the object itself cannot be changed. Instead of trying to update the string itself, update the reference (line=direction;).

What's the difference between next() and nextLine() methods from Scanner class?

What is the main difference between next() and nextLine()?
My main goal is to read the all text using a Scanner which may be "connected" to any source (file for example).
Which one should I choose and why?

I always prefer to read input using nextLine() and then parse the string.
Using next() will only return what comes before the delimiter (defaults to whitespace). nextLine() automatically moves the scanner down after returning the current line.
A useful tool for parsing data from nextLine() would be str.split("\\s+").
String data = scanner.nextLine();
String[] pieces = data.split("\\s+");
// Parse the pieces
For more information regarding the Scanner class or String class refer to the following links.
Scanner: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html
String: http://docs.oracle.com/javase/7/docs/api/java/lang/String.html

next() can read the input only till the space. It can't read two words separated by a space. Also, next() places the cursor in the same line after reading the input.
nextLine() reads input including space between the words (that is, it reads till the end of line \n). Once the input is read, nextLine() positions the cursor in the next line.
For reading the entire line you can use nextLine().

From JavaDoc:
A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace.
next(): Finds and returns the next complete token from this scanner.
nextLine(): Advances this scanner past the current line and returns the input that was skipped.
So in case of "small example<eol>text" next() should return "small" and nextLine() should return "small example"

The key point is to find where the method will stop and where the cursor will be after calling the methods.
All methods will read information which does not include whitespace between the cursor position and the next default delimiters(whitespace, tab, \n--created by pressing Enter). The cursor stops before the delimiters except for nextLine(), which reads information (including whitespace created by delimiters) between the cursor position and \n, and the cursor stops behind \n.
For example, consider the following illustration:
|23_24_25_26_27\n
| -> the current cursor position
_ -> whitespace
stream -> Bold (the information got by the calling method)
See what happens when you call these methods:
nextInt()
read 23|_24_25_26_27\n
nextDouble()
read 23_24|_25_26_27\n
next()
read 23_24_25|_26_27\n
nextLine()
read 23_24_25_26_27\n|
After this, the method should be called depending on your requirement.

What I have noticed apart from next() scans only upto space where as nextLine() scans the entire line is that next waits till it gets a complete token where as nextLine() does not wait for complete token, when ever '\n' is obtained(i.e when you press enter key) the scanner cursor moves to the next line and returns the previous line skipped. It does not check for the whether you have given complete input or not, even it will take an empty string where as next() does not take empty string
public class ScannerTest {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int cases = sc.nextInt();
String []str = new String[cases];
for(int i=0;i<cases;i++){
str[i]=sc.next();
}
}
}
Try this program by changing the next() and nextLine() in for loop, go on pressing '\n' that is enter key without any input, you can find that using nextLine() method it terminates after pressing given number of cases where as next() doesnot terminate untill you provide and input to it for the given number of cases.

next() and nextLine() methods are associated with Scanner and is used for getting String inputs. Their differences are...
next() can read the input only till the space. It can't read two words separated by space. Also, next() places the cursor in the same line after reading the input.
nextLine() reads input including space between the words (that is, it reads till the end of line \n). Once the input is read, nextLine() positions the cursor in the next line.
import java.util.Scanner;
public class temp
{
public static void main(String arg[])
{
Scanner sc=new Scanner(System.in);
System.out.println("enter string for c");
String c=sc.next();
System.out.println("c is "+c);
System.out.println("enter string for d");
String d=sc.next();
System.out.println("d is "+d);
}
}
Output:
enter string for c
abc def
c is abc
enter string for d
d is def
If you use nextLine() instead of next() then
Output:
enter string for c
ABC DEF
c is ABC DEF
enter string for d
GHI
d is GHI

In short: if you are inputting a string array of length t, then Scanner#nextLine() expects t lines, each entry in the string array is differentiated from the other by enter key.And Scanner#next() will keep taking inputs till you press enter but stores string(word) inside the array, which is separated by whitespace.
Lets have a look at following snippet of code
Scanner in = new Scanner(System.in);
int t = in.nextInt();
String[] s = new String[t];
for (int i = 0; i < t; i++) {
s[i] = in.next();
}
when I run above snippet of code in my IDE (lets say for string length 2),it does not matter whether I enter my string as
Input as :- abcd abcd or
Input as :-
abcd
abcd
Output will be like
abcd
abcd
But if in same code we replace next() method by nextLine()
Scanner in = new Scanner(System.in);
int t = in.nextInt();
String[] s = new String[t];
for (int i = 0; i < t; i++) {
s[i] = in.nextLine();
}
Then if you enter input on prompt as -
abcd abcd
Output is :-
abcd abcd
and if you enter the input on prompt as
abcd (and if you press enter to enter next abcd in another line, the input prompt will just exit and you will get the output)
Output is:-
abcd

From javadocs
next() Returns the next token if it matches the pattern constructed from the specified string.
nextLine() Advances this scanner past the current line and returns the input that was skipped.
Which one you choose depends which suits your needs best. If it were me reading a whole file I would go for nextLine until I had all the file.

From the documentation for Scanner:
A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace.
From the documentation for next():
A complete token is preceded and followed by input that matches the delimiter pattern.

Just for another example of Scanner.next() and nextLine() is that like below :
nextLine() does not let user type while next() makes Scanner wait and read the input.
Scanner sc = new Scanner(System.in);
do {
System.out.println("The values on dice are :");
for(int i = 0; i < n; i++) {
System.out.println(ran.nextInt(6) + 1);
}
System.out.println("Continue : yes or no");
} while(sc.next().equals("yes"));
// while(sc.nextLine().equals("yes"));

Both functions are used to move to the next Scanner token.
The difference lies in how the scanner token is generated
next() generates scanner tokens using delimiter as White Space
nextLine() generates scanner tokens using delimiter as '\n' (i.e Enter
key presses)

A scanner breaks its input into tokens using a delimiter pattern, which is by default known the Whitespaces.
Next() uses to read a single word and when it gets a white space,it stops reading and the cursor back to its original position.
NextLine() while this one reads a whole word even when it meets a whitespace.the cursor stops when it finished reading and cursor backs to the end of the line.
so u don't need to use a delimeter when you want to read a full word as a sentence.you just need to use NextLine().
public static void main(String[] args) {
// TODO code application logic here
String str;
Scanner input = new Scanner( System.in );
str=input.nextLine();
System.out.println(str);
}

I also got a problem concerning a delimiter.
the question was all about inputs of
enter your name.
enter your age.
enter your email.
enter your address.
The problem
I finished successfully with name, age, and email.
When I came up with the address of two words having a whitespace (Harnet street) I just got the first one "harnet".
The solution
I used the delimiter for my scanner and went out successful.
Example
public static void main (String args[]){
//Initialize the Scanner this way so that it delimits input using a new line character.
Scanner s = new Scanner(System.in).useDelimiter("\n");
System.out.println("Enter Your Name: ");
String name = s.next();
System.out.println("Enter Your Age: ");
int age = s.nextInt();
System.out.println("Enter Your E-mail: ");
String email = s.next();
System.out.println("Enter Your Address: ");
String address = s.next();
System.out.println("Name: "+name);
System.out.println("Age: "+age);
System.out.println("E-mail: "+email);
System.out.println("Address: "+address);
}

The basic difference is next() is used for gettting the input till the delimiter is encountered(By default it is whitespace,but you can also change it) and return the token which you have entered.The cursor then remains on the Same line.Whereas in nextLine() it scans the input till we hit enter button and return the whole thing and places the cursor in the next line.
**
Scanner sc=new Scanner(System.in);
String s[]=new String[2];
for(int i=0;i<2;i++){
s[i]=sc.next();
}
for(int j=0;j<2;j++)
{
System.out.println("The string at position "+j+ " is "+s[j]);
}
**
Try running this code by giving Input as "Hello World".The scanner reads the input till 'o' and then a delimiter occurs.so s[0] will be "Hello" and cursor will be pointing to the next position after delimiter(that is 'W' in our case),and when s[1] is read it scans the "World" and return it to s[1] as the next complete token(by definition of Scanner).If we use nextLine() instead,it will read the "Hello World" fully and also more till we hit the enter button and store it in s[0].
We may give another string also by using nextLine(). I recommend you to try using this example and more and ask for any clarification.

The difference can be very clear with the code below and its output.
public static void main(String[] args) {
List<String> arrayList = new ArrayList<>();
List<String> arrayList2 = 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);
}
product = input.nextLine();
System.out.println("Enter a product");
while (!product.equalsIgnoreCase("q")) {
arrayList2.add(product);
System.out.println("Enter a product");
product = input.nextLine();
}
System.out.println();
System.out.println();
System.out.println();
System.out.println();
System.out.println("You wrote the following products \n");
for (String naam : arrayList2) {
System.out.println(naam);
}
}
Output:
Enter a product
aaa aaa
Enter a product
Enter a product
bb
Enter a product
ccc cccc ccccc
Enter a product
Enter a product
Enter a product
q
You wrote the following products
aaa
aaa
bb
ccc
cccc
ccccc
Enter a product
Enter a product
aaaa aaaa aaaa
Enter a product
bb
Enter a product
q
You wrote the following products
aaaa aaaa aaaa
bb
Quite clear that the default delimiter space is adding the products separated by space to the list when next is used, so each time space separated strings are entered on a line, they are different strings.
With nextLine, space has no significance and the whole line is one string.

Ignore space, blanks

Does anybody know how i could make scanner ignore space? I wanna type a first and second name, but scanner wont let me, i want to save the full name
String name;
System.out.print("Enter name: ");
name = scan.next(); //Ex: John Smith
System.out.println(name);
Edit:
New problem.. While using nextLine in my extended program, nextLine just ignores the whole question and moves on without a chance to scan the name.

Scanner#next() splits lines around whitespace. Scanner.nextLine() does not, therefore leaving spaces in.
name = scan.nextLine(); //Ex: John Smith

Well, first your System.out.print(); call is flawed. Everything inside must be inside quotations
System.out.print("Enter name: ");
scan.next() gets the next character in the stream, whereas scan.nextLine() gets the next line (terminated by an EOL character), which may be more helpful to you.
After that, you can create an array of words, like
String[] broken = name.split(" ");
which will place into broken all of the words that you've typed in delimited by spaces.
Then you can go something like
for(int i = 0; i < broken.size; i++)
{
System.out.print(broken[i] + " ");
}
System.out.println();

Scanner.next delimits using whitespaces, to read a full line you can use:
name = scan.nextLine();

use scanner.nextLine() which reads full line, instead of scan.next();
Example:
name = scan.nextLine();
Read oracle documentation for Scanner class for available methods.

sounds like you want to read the entire line (minus the line ending). if someone enters, "helen r. smith", you can read the line in with:
name = scan.nextLine();

YOU CAN DO LIKE THIS
import java.util.*;
class scanner2
{
public static void main(String args[])
{
Scanner in= new Scanner(System.in);
System.out.println("enter the name");
String name= in.nextLine();//for name with spaces with more than one word or for one word.
System.out.println("enter single word");
String rl= in.next();//single word name
System.out.println("name is "+name+" rl is "+rl);
}
}
Execute it you will get your answer.