How do I append data to a text file?

By Wayan in Core API, IO 0 Comment

One of the common task related to a text file is to append or add some contents to the file. It’s really simple to do this in Java using a FileWriter class. This class has a constructor that accept a boolean parameter call append. By setting this value to true a new data will be appended at the end of the file when we write a new data to it.

Let’s see an example.

package org.kodejava.io;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class AppendFileExample {
    public static void main(String[] args) {
        File file = new File("user.txt");

        try (FileWriter writer = new FileWriter(file, true)) {
            writer.write("username=kodejava;password=secret" + System.lineSeparator());
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I use LineNumberReader class to read file?

By Wayan in Core API, IO 0 Comment

In this example we use LineNumberReader class to read file contents. What we try to do here is to get the line number of the read data. Instead of introducing another variable; an integer for instance; to keep track the line number we can utilize the LineNumberReader class. This class offers the getLineNumber() method to know the current line of the data that is read.

package org.kodejava.io;

import java.io.FileReader;
import java.io.LineNumberReader;
import java.util.Objects;

public class LineNumberReaderExample {
    public static void main(String[] args) throws Exception {
        // We'll read a file called student.csv that contains our
        // student information data.
        String filename = Objects.requireNonNull(Thread.currentThread().getContextClassLoader()
                .getResource("student.csv")).getFile();

        // To create the FileReader we can pass in our student data
        // file to the reader. Next we pass the reader into our
        // LineNumberReader class.
        try (FileReader fileReader = new FileReader(filename);
             LineNumberReader lineNumberReader = new LineNumberReader(fileReader)) {
            // If we set the line number of the LineNumberReader here
            // we'll got the line number start from the defined line
            // number + 1

            //lineNumberReader.setLineNumber(400);

            String line;
            while ((line = lineNumberReader.readLine()) != null) {
                // We print out the student data and show what line
                // is currently read by our program.
                System.out.printf("Line Number %s: %s%n", lineNumberReader.getLineNumber(), line);
            }
        }
    }
}

The /resources/student.csv file:

Alice, 7
Bob, 8
Carol, 5
Doe, 6
Earl, 6
Malory, 8

And here is the result of our code snippet above:

Line Number 1: Alice, 7
Line Number 2: Bob, 8
Line Number 3: Carol, 5
Line Number 4: Doe, 6
Line Number 5: Earl, 6
Line Number 6: Malory, 8

How do I get total space and free space of my disk?

By Wayan in Core API, IO 0 Comment 
package org.kodejava.io;

import java.io.File;

public class FreeSpaceExample {
    public static void main(String[] args) {
        // We create an instance of a File to represent a partition
        // of our file system. For instance here we used a drive D:
        // as in Windows operating system. 
        File file = new File("D:");

        // Using the getTotalSpace() we can get an information of
        // the actual size of the partition, and we convert it to
        // mega bytes. 
        long totalSpace = file.getTotalSpace() / (1024 * 1024);

        // Next we get the free disk space as the name of the
        // method shown us, and also get the size in mega bytes.
        long freeSpace = file.getFreeSpace() / (1024 * 1024);

        // Just print out the values.
        System.out.println("Total Space = " + totalSpace + " Mega Bytes");
        System.out.println("Free Space = " + freeSpace + " Mega Bytes");
    }
}

Here is the result of the program:

Total Space = 1907605 Mega Bytes
Free Space = 946213 Mega Bytes

How do I rename a file or directory?

By Wayan in Core API, IO 0 Comment 
package org.kodejava.io;

import java.io.File;
import java.io.IOException;

public class FileRenameExample {
    public static void main(String[] args) throws IOException {
        // Creates a new file called OldHouses.csv
        File oldFile = new File("OldHouses.csv");
        boolean created = oldFile.createNewFile();
        System.out.println("File created? " + created);

        // Creates the target file.
        File newFile = new File("NewHouses.csv");

        // The renameTo() method renames file or directory to a
        // new name by passing the new destination file.
        boolean renamed = oldFile.renameTo(newFile);
        System.out.println("File renamed? " + renamed);
    }
}

How do I check if a file is hidden?

By Wayan in Core API, IO 0 Comment

The File.isHidded() method checks to see if the file represented by aFile object is a hidden file. The definition of hidden is varied between operating systems. On UNIX based systems, a file is considered to be hidden when their name begins with a period character ('.'). On Windows operating system, a file is considered to be hidden if it has been marked hidden in the filesystem.

This File.isHidden() method returns true if and only if the file denoted by this File object is hidden according to the conventions of the underlying platform.

package org.kodejava.io;

import java.io.File;
import java.io.IOException;

public class FileHiddenExample {
    public static void main(String[] args) throws IOException {
        File file = new File("Hidden.txt");
        file.createNewFile();

        // We are using the isHidden() method to check whether a file
        // is hidden.
        if (file.isHidden()) {
            System.out.println("File is hidden!");
        } else {
            System.out.println("File is not hidden!");
        }
    }
}

If you want to set the file attribute to hidden in Windows operating system you can see it in the following example: How do I set the value of file attributes?