How can I change file attribute to read only?

By Wayan in Core API, IO 0 Comment

This code demonstrate how we can modify file attribute to be read only. File class has a setReadOnly() method to make file read only and a canWrite() method to know whether it is writable or not.

package org.kodejava.io;

import java.io.File;

public class FileReadOnlyExample {
    public static void main(String[] args) throws Exception {
        File file = new File("ReadOnly.txt");

        // Create a file only if it doesn't exist.
        boolean created = file.createNewFile();

        // Set file attribute to read only so that it cannot be written
        boolean succeeded = file.setReadOnly();

        // We are using the canWrite() method to check whether we can
        // modified file content.
        if (file.canWrite()) {
            System.out.println("File is writable!");
        } else {
            System.out.println("File is in read only mode!");
        }
    }
}

This code snippet print the following output:

File is in read only mode!

How do I know the memory size in virtual machine?

By Wayan in Core API, Lang Package 0 Comment

If you want to know the free memory, and the total memory available in the Java runtime environment then you can use the following code snippet to check.

package org.kodejava.lang;

public class MemoryExample {
    public static void main(String[] args) {
        long freeMemory = Runtime.getRuntime().freeMemory();
        long totalMemory = Runtime.getRuntime().totalMemory();

        System.out.println("Free Memory  = " + freeMemory);
        System.out.println("Total Memory = " + totalMemory);
    }
}

Here is the result of the code snippet above:

Free Memory  = 1018439896
Total Memory = 1029177344

How do I ping a host?

By Wayan in Core API, Networking 0 Comment

Since Java 1.5 (Tiger) the java.net.InetAddress class introduces isReachable() method that can be used to ping or check if the address specified by the InetAddress is reachable.

package org.kodejava.net;

import java.net.InetAddress;

public class PingExample {
    public static void main(String[] args) {
        try {
            InetAddress address = InetAddress.getByName("172.16.2.0");

            // Try to reach the specified address within the timeout
            // period. If during this period the address cannot be
            // reach then the method returns false.
            boolean reachable = address.isReachable(10000);

            System.out.println("Is host reachable? " + reachable);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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 change the cursor shape in Swing?

By Wayan in Swing 0 Comment

Using the following code snippet you can change the shape of mouse cursor in your Java Swing desktop application. The cursor is represented by the java.awt.Cursor class. Create an instance of Cursor using the new operator and pass the cursor type to the Cursor class constructor.

We can change Swing’s objects (JLabel, JTextArea, JButton, etc) cursor using the setCursor() method. In the snippet below, for demonstration, we change the cursor of the JFrame. Your mouse pointer or cursor shape will be changed if you positioned inside the frame.

A collections of cursor shape defined in the java.awt.Cursor class, such as:

  • Cursor.DEFAULT_CURSOR
  • Cursor.HAND_CURSOR
  • Cursor.CROSSHAIR_CURSOR
  • Cursor.WAIT_CURSOR
  • etc
package org.kodejava.swing;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import java.awt.Cursor;

public class ChangeCursor extends JFrame {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            ChangeCursor frame = new ChangeCursor();
            frame.setTitle("Change Cursor");
            frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            frame.setSize(500, 500);

            // Here we create a hand shaped cursor!
            Cursor cursor = new Cursor(Cursor.HAND_CURSOR);
            frame.setCursor(cursor);
            frame.setVisible(true);
        });
    }
}