How do I create a queue using LinkedList class?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.LinkedList;
import java.util.Queue;

public class QueueDemo {
    public static void main(String[] args) {
        // Create an instance of a queue, ere we use the LinkedList class which
        // implements the Queue interface. Add some elements to the queue using
        // the offer method.
        Queue<String> queue = new LinkedList<>();
        queue.offer("First visitor");
        queue.offer("Second visitor");
        queue.offer("Third visitor");
        queue.offer("Fourth visitor");

        // Let see the size of our queue
        System.out.println("Size: " + queue.size());

        // The peek and element method read the head of the queue without removing
        // the element. The difference is, if the queue is empty peek method
        // return null while element method throws a NoSuchElementException
        // exception.
        System.out.println("Queue head using peek   : " + queue.peek());
        System.out.println("Queue head using element: " + queue.element());

        // The poll method retrieves and then removes the head of the queue.
        // On the next code will process all the element of the queue. When no
        // item in the queue the poll method will return null.
        Object data;
        while ((data = queue.poll()) != null) {
            System.out.println(data);
        }
    }
}

The code snippet above print the following output:

Size: 4
Queue head using peek   : First visitor
Queue head using element: First visitor
First visitor
Second visitor
Third visitor
Fourth visitor

How do I use the Stack class in Java?

By Wayan in Core API, Util Package 0 Comment

Stack is an extension of the java.util.Vector class that provided a LIFO (last-in-first-out) data structure. This class provide the usual method such as push() and pop(). The peek method is used the get the top element of the stack without removing the item.

package org.kodejava.util;

import java.util.Stack;

public class StackExample {
    public static void main(String[] args) {
        Stack<Integer> stack = new Stack<>();

        // We stored some values in the stack object.
        for (int i = 0; i < 10; i++) {
            stack.push(i);
            System.out.print(i + " ");
        }
        System.out.println();

        // Searching for an item in the stack. The position returned
        // as the distance from the top of the stack. Here we search
        // for the 3 number in the stack which is in the 7th row of
        // the stack.
        int position = stack.search(3);
        System.out.println("Search result position: " + position);

        // The current top value of the stack
        System.out.println("Stack top: " + stack.peek());

        // Here we're popping out all the stack object items.
        while (!stack.empty()) {
            System.out.print(stack.pop() + " ");
        }
    }
}

The result of the code snippet:

0 1 2 3 4 5 6 7 8 9 
Search result position: 7
Stack top: 9
9 8 7 6 5 4 3 2 1 0

How do I convert string date to long value?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class StringDateToLong {
    public static void main(String[] args) {
        // Here we have a string date, and we want to covert it to long value
        String today = "25/09/2021";

        // Create a SimpleDateFormat which will be used to convert the string to
        // a date object.
        DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
        try {
            // The SimpleDateFormat parse the string and return a date object.
            // To get the date in long value just call the getTime method of
            // the Date object.
            Date date = formatter.parse(today);
            long dateInLong = date.getTime();

            System.out.println("Date         = " + date);
            System.out.println("Date in Long = " + dateInLong);
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

The result of the code snippet:

Date         = Sat Sep 25 00:00:00 CST 2021
Date in Long = 1632499200000

How do I create a scheduled task using timer?

By Wayan in Core API, Util Package 0 Comment

This example show you how to create a simple class for scheduling a task using Timer and TimerTask class.

package org.kodejava.util;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class TimerExample extends TimerTask {
    private final DateFormat formatter = new SimpleDateFormat("hh:mm:ss a");

    public static void main(String[] args) {
        // Create an instance of TimerTask implementor.
        TimerTask task = new TimerExample();

        // Create a new timer to schedule the TimerExample instance at a
        // periodic time every 5000 milliseconds (5 seconds) and start it
        // immediately
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(task, new Date(), 5000);
    }

    /**
     * This method is the implementation of a contract defined in the 
     * TimerTask class. This in the entry point of the task execution.
     */
    public void run() {
        // To make the example simple we just print the current time.
        System.out.println(formatter.format(new Date()));
    }
}

Here is the result printed by the code snippet above:

09:53:28 AM
09:53:33 AM
09:53:38 AM
09:53:43 AM
09:53:48 AM

How do I get the last day of a month?

By Wayan in Core API, Util Package 2 Comments 
package org.kodejava.util;

import java.text.DateFormatSymbols;
import java.util.Calendar;

public class LastDayOfMonth {
    public static void main(String[] args) {
        // Get a calendar instance
        Calendar calendar = Calendar.getInstance();

        // Get the last date of the current month. To get the last date for a
        // specific month you can set the calendar month using calendar object
        // calendar.set(Calendar.MONTH, theMonth) method.
        int lastDate = calendar.getActualMaximum(Calendar.DATE);

        // Set the calendar date to the last date of the month so then we can
        // get the last day of the month
        calendar.set(Calendar.DATE, lastDate);
        int lastDay = calendar.get(Calendar.DAY_OF_WEEK);

        // Print the current date and the last date of the month
        System.out.println("Last Date: " + calendar.getTime());

        // The lastDay will be in a value from 1 to 7 where 1 = Sunday and 7 =
        // Saturday. The first day of the week is based on the locale.
        System.out.println("Last Day : " + lastDay);

        // Get weekday name
        DateFormatSymbols dfs = new DateFormatSymbols();
        System.out.println("Last Day : " + dfs.getWeekdays()[lastDay]);
    }
}

Here is the output of the code snippet above:

Last Date: Thu Sep 30 06:44:05 CST 2021
Last Day : 5
Last Day : Thursday