Objektorienteeritud programmeerimine (Narva Kolledž) 2019/20 kevad

Chapter 4

Files

In Java, there are several possibilities to communicate with files. In this section, we consider 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 
    // we will study these two words in detail a bit 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 encoding
        // the keyword "try" attempts to open and close the file given as an argument
        try (PrintWriter pw = new PrintWriter(myFile, "UTF-8")) {

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

        // create an instance of Scanner class to read from a file
        // the arguments are: the reference to the file and encoding
        try (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 to read from input
                String line = sc.nextLine(); // method nextLine returns the line that was read
                System.out.println(line);
            }
        }
    }
}

Chapter 4