How do I determine whether a string is a palindrome?

By Wayan in Core API, Lang Package 0 Comment

This code checks a string to determine if it is a palindrome or not. A palindrome is a word, phrase, or sequence that reads the same backward as forward.

package org.kodejava.lang;

public class PalindromeChecker {

    public static void main(String[] args) {
        String text = "Sator Arepo Tenet Opera Rotas";

        PalindromeChecker checker = new PalindromeChecker();
        System.out.println("Is palindrome = " + checker.isPalindrome(text));
    }

    /**
     * This method checks the string for palindrome. We use StringBuilder to
     * reverse the original string.
     *
     * @param text a text to be checked for palindrome.
     * @return <code>true</code> if a text is palindrome.
     */
    private boolean isPalindrome(String text) {
        System.out.println("Original text = " + text);

        String reverse = new StringBuilder(text).reverse().toString();
        System.out.println("Reverse text  = " + reverse);

        // Compare the original text with the reverse one and ignoring its case
        return text.equalsIgnoreCase(reverse);
    }
}

How do I create a thread by implementing Runnable interface?

By Wayan in Core API, Lang Package 0 Comment

Here is the second way for creating a thread. We create an object that implements the java.lang.Runnable interface. For another example see How do I create a thread by extending Thread class?.

package org.kodejava.lang;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class TimeThread implements Runnable {
    private final DateFormat df = new SimpleDateFormat("hh:mm:ss");

    // The run() method will be invoked when the thread of this runnable object
    // is started.
    @Override
    public void run() {
        while (true) {
            Calendar calendar = Calendar.getInstance();
            System.out.format("Now is: %s.%n", df.format(calendar.getTime()));

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        TimeThread time = new TimeThread();

        Thread thread = new Thread(time);
        thread.start();
    }
}

An example result of this code are:

Now is: 07:18:39.
Now is: 07:18:40.
Now is: 07:18:41.
Now is: 07:18:42.
Now is: 07:18:43.

How do I create a thread by extending Thread class?

By Wayan in Core API, Lang Package 0 Comment

There are two ways that we can use tho create a thread. First is by extending the java.lang.Thread class and the second way is by creating a class that implements the java.lang.Runnable interface. See How do I create a thread by implementing Runnable interface?

In this example we’ll extend the Thread class. To run a code in a thread we need to provide the run() method in our class. Let’s see the code below.

package org.kodejava.lang;

public class NumberPrinter extends Thread {
    private final String threadName;
    private final int delay;

    public NumberPrinter(String threadName, int delay) {
        this.threadName = threadName;
        this.delay = delay;
    }

    // The run() method will be invoked when the thread is started.
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println("Thread [" + threadName + "] = " + i);

            try {
                Thread.sleep(delay);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        NumberPrinter printerA = new NumberPrinter("A", 1000);
        NumberPrinter printerB = new NumberPrinter("B", 750);

        printerA.start();
        printerB.start();
    }
}

The example result of our code is:

Thread [B] = 0
Thread [A] = 0
Thread [B] = 1
Thread [A] = 1
Thread [B] = 2
Thread [A] = 2
Thread [B] = 3
Thread [B] = 4
Thread [A] = 3
Thread [B] = 5
Thread [A] = 4
Thread [B] = 6
Thread [A] = 5
Thread [B] = 7
Thread [B] = 8
Thread [A] = 6
Thread [B] = 9
Thread [A] = 7
Thread [A] = 8
Thread [A] = 9

How do I get Java Home directory?

By Wayan in Core API, Lang Package 0 Comment

To get Java Home directory we can obtain it from system properties using the java.home key.

package org.kodejava.lang;

public class JavaHomeDirectory {
    public static void main(String[] args) {
        String javaHome = System.getProperty("java.home");
        System.out.println("JAVA HOME = " + javaHome);
    }
}

On my computer this code give me the following output:

JAVA HOME = C:\Program Files\Java\jdk-17

How do I get the username of operating system active user?

By Wayan in Core API, Lang Package 0 Comment

This example show you how to get operating system active user’s login name. We can obtain the username of current user by reading system properties using the user.name key.

package org.kodejava.lang;

public class GettingUserName {
    public static void main(String[] args) {
        String username = System.getProperty("user.name");
        System.out.println("username = " + username);
    }
}