How do I read the status of Scroll Lock key?

By Wayan in AWT, Core API 0 Comment

This example show you how to detect if the Scroll Lock key is in active mode. If you run the program you will get an output telling you that the Scroll Lock button is active or not active.

package org.kodejava.awt;

import java.awt.Toolkit;
import java.awt.event.KeyEvent;

public class ScrollLockState {
    public static void main(String[] args) {
        Toolkit toolkit = Toolkit.getDefaultToolkit();

        // Get the locking state of the Scroll Lock button. This method 
        // return boolean true value if it is "on".
        boolean isOn = toolkit.getLockingKeyState(KeyEvent.VK_SCROLL_LOCK);

        System.out.println("ScrollLock button is " + (isOn ? "on" : "off"));
    }
}

How do I read the status of Num Lock key?

By Wayan in AWT, Core API 2 Comments

This example show you how to detect if the Num Lock key is in active mode. If you run the program you will get an output telling you that the Num Lock button is active or not active.

package org.kodejava.awt;

import java.awt.Toolkit;
import java.awt.event.KeyEvent;

public class NumLockState {
    public static void main(String[] args) {
        Toolkit toolkit = Toolkit.getDefaultToolkit();

        // Get the locking state of the Num Lock button. This method
        // return boolean true value if it is "on".
        boolean isOn = toolkit.getLockingKeyState(KeyEvent.VK_NUM_LOCK);

        System.out.println("NumLock button is " + (isOn ? "on" : "off"));
    }
}

How do I read the status of Caps Lock key?

By Wayan in AWT, Core API 0 Comment

This example show you how to detect if the Caps Lock key is in active mode.

package org.kodejava.awt;

import java.awt.Toolkit;
import java.awt.event.KeyEvent;

public class CapsLockState {
    public static void main(String[] args) {
        // Get the locking state of the Caps Lock button. This method
        // return boolean true value if it is "on".
        boolean isOn = Toolkit.getDefaultToolkit().getLockingKeyState(
                KeyEvent.VK_CAPS_LOCK);

        System.out.println("CapsLock button is " + (isOn ? "on" : "off"));
    }
}

How do I read a file into byte array?

By Wayan in Core API, IO 0 Comment 
package org.kodejava.io;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class ReadFileIntoByteArray {
    public static void main(String[] args) throws IOException {
        File file = new File("README.md");
        try (InputStream is = new FileInputStream(file)) {
            if (file.length() > Integer.MAX_VALUE) {
                throw new IOException("File is too large.");
            }

            int offset = 0;
            int bytesRead;
            byte[] bytes = new byte[(int) file.length()];
            while (offset < bytes.length
                    && (bytesRead = is.read(bytes, offset, bytes.length - offset)) >= 0) {
                offset += bytesRead;
            }
        }
    }
}

How do I sort a java.util.Enumeration?

By Wayan in Core API, Util Package 1 Comment

In this code snippet you will see how to sort the content of an Enumeration object. We start by creating a random numbers and stored it in a Vector. We use these numbers and create a Enumeration object by calling Vector‘s elements() method. We convert it to java.util.List and then sort the content of the List using Collections.sort() method. Here is the complete code snippet.

package org.kodejava.util;

import java.util.*;

public class EnumerationSort {
    public static void main(String[] args) {
        // Creates random data for sorting source. Will use java.util.Vector
        // to store the random integer generated.
        Random random = new Random();
        Vector<Integer> data = new Vector<>();
        for (int i = 0; i < 10; i++) {
            data.add(Math.abs(random.nextInt()));
        }

        // Get the enumeration from the vector object and convert it into
        // a java.util.List. Finally, we sort the list using
        // Collections.sort() method.
        Enumeration<Integer> enumeration = data.elements();
        List<Integer> list = Collections.list(enumeration);
        Collections.sort(list);

        // Prints out all generated number after sorted.
        for (Integer number : list) {
            System.out.println("Number = " + number);
        }
    }
}

An example result of the code above is:

Number = 20742427
Number = 163885840
Number = 204704456
Number = 560032429
Number = 601762809
Number = 1300593322
Number = 1371678147
Number = 1786580321
Number = 1786731301
Number = 1856215303

How do I sort LinkedList elements?

By Wayan in Core API, Util Package 0 Comment

To sort the elements of LinkedList we can use the Collections.sort(List<T> list) static methods. The default order of the sorting is a descending order.

package org.kodejava.util;

import java.util.LinkedList;
import java.util.Collections;

public class LinkedListSort {
    public static void main(String[] args) {
        LinkedList<String> grades = new LinkedList<>();
        grades.add("E");
        grades.add("C");
        grades.add("A");
        grades.add("F");
        grades.add("B");
        grades.add("D");

        System.out.println("Before sorting:");
        System.out.println("===============");
        for (String grade : grades) {
            System.out.println("Grade = " + grade);
        }

        // Sort the elements of linked list based on its data
        // natural order.
        Collections.sort(grades);

        System.out.println("After sorting:");
        System.out.println("===============");
        for (String grade : grades) {
            System.out.println("Grade = " + grade);
        }
    }
}

The result of the program are:

Before sorting:
===============
Grade = E
Grade = C
Grade = A
Grade = F
Grade = B
Grade = D
After sorting:
===============
Grade = A
Grade = B
Grade = C
Grade = D
Grade = E
Grade = F

How do I get the first and the last element of a LinkedList?

By Wayan in Core API, Util Package 0 Comment

The get the first element we can use the LinkedList.getFirst() method and to get the last element we can use the LinkedList.getLast() method.

package org.kodejava.util;

import java.util.LinkedList;

public class LinkedListGetFirstLast {
    public static void main(String[] args) {
        LinkedList<String> names = new LinkedList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Carol");
        names.add("Mallory");

        // Get the first and the last element of the linked list
        String first = names.getFirst();
        String last = names.getLast();

        System.out.println("First member = " + first);
        System.out.println("Last member  = " + last);
    }
}

The program will print the following result:

First member = Alice
Last member  = Mallory

How do I reverse the order of LinkedList elements?

By Wayan in Core API, Util Package 0 Comment

To reverse the order of LinkedList elements we can use the reverse(List<?> list) static method of java.util.Collections class. Here is the example:

package org.kodejava.util;

import java.util.LinkedList;
import java.util.Collections;

public class LinkedListReverseOrder {
    public static void main(String[] args) {
        LinkedList<String> grades = new LinkedList<>();
        grades.add("A");
        grades.add("B");
        grades.add("C");
        grades.add("D");
        grades.add("E");
        grades.add("F");

        System.out.println("Output in original order:");
        System.out.println("=========================");
        for (String grade : grades) {
            System.out.println("Grade = " + grade);
        }

        // Reverse the element order in the linked list object.
        Collections.reverse(grades);

        System.out.println("Output in reverse order:");
        System.out.println("=========================");
        for (String grade : grades) {
            System.out.println("Grade = " + grade);
        }
    }
}

Here is the output of the program:

Output in original order:
=========================
Grade = A
Grade = B
Grade = C
Grade = D
Grade = E
Grade = F
Output in reverse order:
=========================
Grade = F
Grade = E
Grade = D
Grade = C
Grade = B
Grade = A

How do I remove an item from LinkedList?

By Wayan in Core API, Util Package 0 Comment

This program shows you how to use the remove(int index) method of LinkedList class to remove an item at specified index from linked list object.

package org.kodejava.util;

import java.util.LinkedList;

public class LinkedListRemove {
    public static void main(String[] args) {
        LinkedList<String> names = new LinkedList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Carol");
        names.add("Mallory");

        System.out.println("Original values are:");
        System.out.println("====================");
        for (String name : names) {
            System.out.println("Name = " + name);
        }

        // Remove Carol from the linked list.
        names.remove(2);

        System.out.println("New values are:");
        System.out.println("====================");
        for (String name : names) {
            System.out.println("Name = " + name);
        }
    }
}

The result of the program above are:

Original values are:
====================
Name = Alice
Name = Bob
Name = Carol
Name = Mallory
New values are:
====================
Name = Alice
Name = Bob
Name = Mallory

How do I insert an item into LinkedList?

By Wayan in Core API, Util Package 0 Comment

To insert an item at any position into a linked list object we can use the add(int index, Object o) method. This method takes the index to where the new object to be inserted and the object to be inserted itself.

package org.kodejava.util;

import java.util.LinkedList;

public class LinkedListAddDemo {
    public static void main(String[] args) {
        LinkedList<String> names = new LinkedList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Mallory");

        System.out.println("Original values are:");
        System.out.println("====================");
        for (String name : names) {
            System.out.println("Name = " + name);
        }

        // Add a new item to the list at index number 2. Because
        // a list are 0 based index Carol will be inserted after
        // Bob.
        names.add(2, "Carol");

        System.out.println("New values are:");
        System.out.println("====================");
        for (String name : names) {
            System.out.println("Name = " + name);
        }
    }
}

The result of our program are:

Original values are:
====================
Name = Alice
Name = Bob
Name = Mallory
New values are:
====================
Name = Alice
Name = Bob
Name = Carol
Name = Mallory