Objektorienteeritud programmeerimine (Narva Kolledž) 2017/18 kevad

Session 4

Files

In Java, there are several opportunities for communicate with files. In this section, we will get to know only one way how to get data from a file and write data into a file.

import java.io.File;            // import package that handles Files
import java.io.PrintWriter;     // import package that can write into a file
import java.util.Scanner;       // import package that can read from a file


public class ReadWriteFile {

    // add two words into the header of main method to handle errors (will study in detail later)
    public static void main(String[] args) throws Exception {

        // create an instance of File class and define the file to create connection with
        File myFile = new File("c:/temp/mydata.txt");

        // check if the file already exists
        if (myFile.exists())
            System.out.println("This file already exists in this folder.");
        else
            System.out.println("This file does not exist in this folder.");

        // to write into a file, create an instance of PrintWriter class 
        // the arguments are: the reference to the file and encording
        PrintWriter pw = new PrintWriter(myFile, "UTF-8");

        // write into the file
        pw.print("Kerese ");
        pw.println("street");

        // close the connection witht he file
        pw.close();


        // to read from a file, create an instance of Scanner class and
        // the arguments are: the reference to the file and encording
        Scanner sc = new Scanner(myFile, "UTF-8");

        // read data from the file using a loop
        while (sc.hasNextLine()) {  // method hasNextLine returns a boolean value
                                    // if the Scanner has another line in its input to read
            String line = sc.nextLine(); // method nextLine returns the line that was read
            System.out.println(line);
        }

        // close the connection with the file
        sc.close();

    }
}

Session 4