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 find and replace string?

By Wayan in Regex 0 Comment

The code below demonstrates the use Matcher.appendReplacement() and Matcher.appendTail() methods to create a program to find and replace a sub string within a string.

Another solution that can be used to search and replace a string can be found on the following example: How do I create a string search and replace using regex?.

package org.kodejava.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class AppendReplacementExample {
    public static void main(String[] args) {
        // Create a Pattern instance
        Pattern pattern = Pattern.compile("[Pp]en");

        // Create matcher object
        String input = "Please use your Pen to answer the question, " +
                "black pen is preferred.";
        Matcher matcher = pattern.matcher(input);
        StringBuilder builder = new StringBuilder();

        // Find and replace the text that match the pattern
        while (matcher.find()) {
            matcher.appendReplacement(builder, "pencil");
        }

        // This method reads characters from the input sequence, starting
        // at the beginning position, and appends them to the given string
        // builder. It is intended to be invoked after one or more
        // invocations of the appendReplacement method in order to copy
        // the remainder of the input sequence.
        matcher.appendTail(builder);

        System.out.println("Input : " + input);
        System.out.println("Output: " + builder);
    }
}

Here is the result of the above code:

Input : Please use your Pen to answer the question, black pen is preferred.
Output: Please use your pencil to answer the question, black pencil is preferred.

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();
        }
    }
}