Java Scanner example – read & write contents to/ from file (example)

• Scanner is text parser which used to parse primitives & strings using regular expression.
• Scanner split the input into token using delimiter pattern.
  • Default pattern delimiter is whitespace.
• We will write content to a file using FileWriter class.
  • Then, we will read content from as file using Scanner class.
• Scanner class extends object & implements Closeable & Iterable interface.

Scanner class hierarchy is as follows:

Scanner class constructors (Java IO):

Important methods of Scanner class (Java IO):

Program: Write file & read file in java using Scanner class (example)

package org.learn.io.scan;

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class ReadFileUsingScanner {

    public static void main(String[] args) throws IOException {
        //Write content to file
        writeFileContents();
        //Reading content of file using Scanner class
        readFileContents();
    }

    private static void writeFileContents() throws IOException {

        try (FileWriter fileWriter = new FileWriter("info.txt")) {
            fileWriter.write("10 ");
            fileWriter.write("20.5 ");
            fileWriter.write("Employee ");
            fileWriter.write("50.00 ");
            fileWriter.write("Coffee");
        }
    }

    private static void readFileContents() throws IOException {
        System.out.println("Reading contents of file using Scanner class:");
        try (FileReader fileReader = new FileReader("info.txt");
                Scanner scanner=new Scanner(fileReader)){
            while (scanner.hasNext()) {
                if(scanner.hasNextInt()) {
                    System.out.println(scanner.nextInt());
                } else if(scanner.hasNextDouble()) {
                    System.out.println(scanner.nextDouble());
                } else if(scanner.hasNext()) {
                    System.out.println(scanner.next());
                }
            }
        }
    }
}

Output: Read file in java using Scanner class (example)

Reading contents of file using Scanner class:
10
20.5
Employee
50.0
Coffee