How do I insert a string to a StringBuffer?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

public class StringBufferInsert {
    public static void main(String[] args) {
        StringBuffer buffer = new StringBuffer("kodeava");
        System.out.println("Text before        = " + buffer);

        //  |k|o|d|e|a|v|a|....
        //  0|1|2|3|4|5|6|7|...
        //
        // From the above sequence you can see that the index of the
        // string is started from 0, so when we insert a string in
        // the fourth offset it means it will be inserted after the
        // "e" letter. There are other overload version of this
        // method that can be used to insert other type of data such
        // as char, int, long, float, double, Object, etc.
        buffer.insert(4, "j");
        System.out.println("After first insert = " + buffer);

        // Here we insert a string to the StringBuffer at index 8
        buffer.insert(8, " examples");
        System.out.println("Final result       = " + buffer);
    }
}

The program will print the following output:

Text before        = kodeava
After first insert = kodejava
Final result       = kodejava examples

How do I remove some characters from a StringBuffer?

By Wayan in Core API, Lang Package 0 Comment

The example below show you to remove some elements of the StringBuffer. We can use the delete(int start, int end) method call to remove some characters from the specified start index to end end index. We can also remove a character at the specified index using the deleteCharAt(int index) method call.

package org.kodejava.lang;

public class StringBufferDelete {
    public static void main(String[] args) {
        String text = "Learn Java by Examples";

        // Creates a new instance of StringBuffer and initialize
        // it with some text.
        StringBuffer buffer = new StringBuffer(text);
        System.out.println("Original text  = " + buffer);

        // We'll remove a sub string from this StringBuffer starting
        // from the first character to the 10th character.
        buffer.delete(0, 10);
        System.out.println("After deletion = " + buffer);

        // Removes a char at a specified index from the StringBuffer.
        // In the example below we remove the last character.
        buffer.deleteCharAt(buffer.length() - 1);
        System.out.println("Final result   = " + buffer);
    }
}

Output of the program is:

Original text  = Learn Java by Examples
After deletion =  by Examples
Final result   =  by Example

How do I get char value of a string at a specified position?

By Wayan in Core API, Lang Package 0 Comment

The chartAt() method of the String class returns the char value at the specified index. An index ranges from 0 to length() - 1. If we specified an index beyond of this range a StringIndexOutOfBoundsException exception will be thrown.

These method use zero based index which means the first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing.

package org.kodejava.lang;

public class CharAtExample {
    public static void main(String[] args) {
        String[] colors = {"black", "white", "brown", "green", "yellow", "blue"};

        for (String color : colors) {
            // Get char value of a string at index number 3. We'll get the 
            // fourth character of each color in the array because the 
            // index is zero based.
            char value = color.charAt(3);
            System.out.printf("The fourth char of %s is '%s'.%n", color, value);
        }

    }
}

Here is the program output:

The fourth char of black is 'c'
The fourth char of white is 't'
The fourth char of brown is 'w'
The fourth char of green is 'e'
The fourth char of yellow is 'l'
The fourth char of blue is 'e'

How do I get the extension of a file?

By Wayan in Core API, IO 0 Comment

Below is an example that can be used to get the extension of a file. The code below assume that the extension is the last part of the file name after the last dot symbol. For instance if you have a file named data.txt the extension will be txt, but if you have a file named data.tar.gz the extension will be gz.

package org.kodejava.io;

import java.io.File;

public class FileExtension {
    private static final String EXT_SEPARATOR = ".";

    public static void main(String[] args) {
        File file = new File("data.txt");
        String ext = FileExtension.getFileExtension(file);
        System.out.println("Ext = " + ext);

        file = new File("F:/Temp/Data/data.tar.gz");
        ext = FileExtension.getFileExtension(file);
        System.out.println("Ext = " + ext);

        file = new File("F:/Temp/Data/HelloWorld.java");
        ext = FileExtension.getFileExtension(file);
        System.out.println("Ext = " + ext);
    }

    /**
     * Get the extension of the specified file.
     *
     * @param file a file.
     * @return the extension of the file.
     */
    private static String getFileExtension(File file) {
        if (file == null) {
            return null;
        }

        String name = file.getName();
        int extIndex = name.lastIndexOf(FileExtension.EXT_SEPARATOR);

        if (extIndex == -1) {
            return "";
        } else {
            return name.substring(extIndex + 1);
        }
    }
}

How do I trim the capacity of an ArrayList?

By Wayan in Core API, Util Package 0 Comment

For minimizing the storage used by an ArrayList to the number of its elements we can use the ArrayList.trimToSize() method call. In the code below we create an instance of ArrayList with the initial capacity set to 100. Later we only add five data into the list. To make the capacity of the ArrayList minimized we call the trimToSize() method.

package org.kodejava.util;

import java.util.ArrayList;

public class ListTrimToSize {
    public static void main(String[] args) {
        // Create an ArrayList with the initial capacity of 100.
        ArrayList<String> list = new ArrayList<>(100);
        list.add("A");
        list.add("B");
        list.add("C");
        list.add("D");
        list.add("E");
        list.add("F");

        System.out.println("Size: " + list.size());

        // Trim the capacity of the ArrayList to the size
        // of the ArrayList. We can do this operation to reduce
        // the memory used to store data by the ArrayList.
        list.trimToSize();
    }
}

How do I get process ID of a Java application?

By Wayan in Core API, Management 3 Comments

The code below show you how to get the process ID of a Java application. We can use the ManagementFactory.getRuntimeMXBean().getName() to get the process ID. In Windows the method return a string in the form of [PID]@[MACHINE_NAME].

Since JDK 10, we can use ManagementFactory.getRuntimeMXBean().getPid() method to get the process ID. This method returns the process ID representing the running Java virtual machine.

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;

public class GetProcessID {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();

        // Get name representing the running Java virtual machine.
        // It returns something like 35656@Krakatau. The value before
        // the @ symbol is the PID.
        String jvmName = bean.getName();
        System.out.println("Name = " + jvmName);

        // Extract the PID by splitting the string returned by the
        // bean.getName() method.
        long pid = Long.parseLong(jvmName.split("@")[0]);
        System.out.println("PID  = " + pid);

        // Get the process ID representing the running Java virtual machine.
        // Since JDK 10.
        pid = ManagementFactory.getRuntimeMXBean().getPid();
        System.out.println("PID = " + pid);

    }
}

Here is the result of the code above:

Name = 35656@Krakatau
PID  = 35656
PID  = 35656

How do I print a file using the default registered application?

By Wayan in AWT, Core API 1 Comment

The example code below shows you how to print a file using the default registered application’s print command for the corresponding file type. As an example, on Windows notepad.exe is the default application for printing a .txt file.

To print a file using the default registered application we call the java.awt.Desktop.print(File) method. The print() method takes a parameter of File, which is the reference to a file to be printed. The code snippet below, when run on Windows, will open notepad.exe and print the data.txt file.

package org.kodejava.awt;

import java.awt.*;
import java.io.File;
import java.io.IOException;

public class RunningDefaultAppPrint {
    public static void main(String[] args) {
        File file = new File("data.txt");
        try {
            Desktop desktop = Desktop.getDesktop();

            // Prints a file with the native desktop printing facility, 
            // using the associated application's print command.
            desktop.print(file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I edit a file using the default registered application?

By Wayan in AWT, Core API 0 Comment

For editing a file using the default registered or associated application we can do a call to the java.awt.Desktop.edit(File) method. In the code snippet below we will edit a PNG file. Using the edit() method of the Desktop class will open the default registered application for PNG files. For example on Windows there could be the Windows Paint or GIMP on the Linux operating system.

package org.kodejava.awt;

import java.awt.*;
import java.io.File;
import java.io.IOException;

public class RunningDefaultAppEdit {
    public static void main(String[] args) {
        File file = new File("logo.png");
        try {
            // Edit a file using the default program for the file 
            // type. In the example we will launch a default 
            // registered program to edit a PNG image.
            Desktop desktop = Desktop.getDesktop();
            desktop.edit(file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I open a file using the default registered application?

By Wayan in AWT, Core API 1 Comment

If you want to open a file using the default registered or associated application for those files you can use the Desktop.open(File file) method call. In the example below we’ll ask the Desktop class to open a text file.

package org.kodejava.awt;

import java.awt.*;
import java.io.File;
import java.io.IOException;

public class RunningDefaultAppOpen {
    public static void main(String[] args) {
        // A reference to a text file
        File file = new File("data.txt");

        try {
            Desktop desktop = Desktop.getDesktop();

            // Open a file using the default program for the file type.
            // In the example we will launch a default registered
            // program to open a text file. For example on Windows
            // operating system this call might launch a notepad.exe
            // to open the file.
            desktop.open(file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I launch user-default mail client application?

By Wayan in AWT, Core API 0 Comment

Here is an example using the java.awt.Desktop class to open user’s default mail client application. There are two methods provided, the mail() and the mail(URI uri) methods.

When specifying the URI to the application will be opened with the message field filled with the mailto information. You can refer to the following document for the valid mailto URI scheme http://www.ietf.org/rfc/rfc2368.txt

package org.kodejava.awt;

import java.awt.*;
import java.io.IOException;
import java.net.URI;

public class RunningDefaultMailClient {
    public static void main(String[] args) {
        // Get an instance of Desktop. An UnsupportedOperationException will
        // be thrown if the platform doesn't support Desktop API.
        Desktop desktop = Desktop.getDesktop();

        try {
            // Open user-default mail client application.
            desktop.mail();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Open user-default mail client with the email message fields information.
            String message = "mailto:[email protected][email protected]&subject=First%20Email";
            URI uri = URI.create(message);
            desktop.mail(uri);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}