Reading file with Scanner
From Java 5 onwards java.util.Scanner class can be used to read
file in Java. Earlier we have seen example of reading
file in Java using FileInputStream and reading
file line by line using BufferedInputStream and in this Java tutorial we
will See How can we use Scanner to read files in Java. Scanner is a
utility class in java.util package and provides several
convenient method to read int, long, String, double etc from
source which can be an InputStream,
a file or a String itself. As noted on How
to get input from User, Scanner is also an easy way to read
user input using System.in (InputStream) as source.Main advantage of using Scanner for reading file is that it allows you to change delimiter using useDelimiter() method, So you can use any other delimiter like comma, pipe instead of white space.
How to Read File in Java - Scanner Example
In this Java program, we have used java.util.Scanner to read
file line by line in Java. We have first created a File instance
to represent a text file in Java and than we passed this File instance to java.util.Scanner for
scanning. Scanner provides methods like hasNextLine() and readNextLine() which can
be used to read
file line by line. It's advised to check for next line before reading next
line to avoid NoSuchElementException
in Java. Here is complete code
example of using Scanner to read text file in Java :
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
/**
*
* Java program to read file using Scanner class in Java.
* java.util.Scanner is added on Java 5 and offer convenient method to read data
*
* @author
*/
public class ScannerExample {
public static void main(String args[]) throws FileNotFoundException {
//creating File instance to reference text file in Java
File text = new File("C:/temp/test.txt");
//Creating Scanner instnace to read File in Java
Scanner scnr = new Scanner(text);
//Reading each line of file using Scanner class
int lineNumber = 1;
while(scnr.hasNextLine()){
String line = scnr.nextLine();
System.out.println("line " + lineNumber + " :" + line);
lineNumber++;
}
}
}
Output:
line 1 :--------------------- START-----------------------------------------------------
line 2 :Java provides several way to read files.
line 3 :You can read file using Scanner, FileReader, FileInputStream and BufferedReader.
line 4 :This Java program shows How to read file using java.util.Scanner class.
line 5 :--------------------- END--------------------------------------------------------
import java.io.FileNotFoundException;
import java.util.Scanner;
/**
*
* Java program to read file using Scanner class in Java.
* java.util.Scanner is added on Java 5 and offer convenient method to read data
*
* @author
*/
public class ScannerExample {
public static void main(String args[]) throws FileNotFoundException {
//creating File instance to reference text file in Java
File text = new File("C:/temp/test.txt");
//Creating Scanner instnace to read File in Java
Scanner scnr = new Scanner(text);
//Reading each line of file using Scanner class
int lineNumber = 1;
while(scnr.hasNextLine()){
String line = scnr.nextLine();
System.out.println("line " + lineNumber + " :" + line);
lineNumber++;
}
}
}
Output:
line 1 :--------------------- START-----------------------------------------------------
line 2 :Java provides several way to read files.
line 3 :You can read file using Scanner, FileReader, FileInputStream and BufferedReader.
line 4 :This Java program shows How to read file using java.util.Scanner class.
line 5 :--------------------- END--------------------------------------------------------
This is the content of test.txt file exception line
numbers. You see it doesn't require much coding to read file in Java using Scanner. You just
need to create an instance of Scanner and you are ready to read file.
Further Learning
Complete Java Masterclass
Java Fundamentals: The Java Language
Java In-Depth: Become a Complete Java Engineer!
Other Java IO tutorials you may like
import java.io.FileNotFoundException;
ReplyDeleteWhy is this line put ?? What is the function of it??
Its a library in order the compiler to understand what is File for example
DeleteIt's a library, contains the class FileNotFoundException which is used for throwing a exception in case of not find any input text file.
DeleteThe statement
Deleteimport java.io.FileNotFoundException;
just makes it easier to use the Exception class java.io.FileNotFoundException. It doesn't import any class, it just makes a name easier to use. You just need to write FileNotFoundException instead of the full name.
So it doesn't have anything to do with any Java libraries (Jar files).
When the program create a new File object, it will throw a java.io.FileNotFoundException object which contains an error code if the named file doesn't exists.
As there are no try ... catch that handles that exception in the main method, the method main must then be declared to be expected to generate such an error to everyone that calls the main method.
Here is the old way to read a plain text file in Java. It uses FileInputStream instead of FileReader to read text file.
ReplyDeleteI want to clean & scaning temp file in j2me. What is the code of scaning and cleaning
ReplyDeleteHello, I am making a very slow progress learning java.
ReplyDeleteWould you be able to help me out and let me know why my data is not displayed after writing the code as below? I am trying to read in a ppm picture, which is white and black and where 255 stands for white and 0 for black. I will need to calculate the number of white lines that are longer than 1/3 of the table size:
public
class test {
public static final int X = 512;
int count = 0;
int a = 255;
public static void main(String[] args){
int[] data = getData ("C:\\Users\\Joannna\\Desktop\\inData.ppm");
System.out.println(data.length);
System.out.println(data);
}
public static int[] getData(String path){
try{
Scanner scanner = new Scanner(new File("C:\\Users\\Joannna\\Desktop\\inData.ppm"));
int [] data = new int [X*X];
int i = 0;
while(scanner.hasNextInt()){
data[i++] = scanner.nextInt();
scanner.nextInt();
scanner.nextInt();
}
return data;
}catch(Exception io){
System.out.println(io);
return null;
}
}
}
Good to know your writing.
ReplyDelete