How do I iterate LinkedList elements using ListIterator?

By Wayan in Core API, Util Package 0 Comment

This example show you how to use the ListIterator interface to iterate elements of a LinkedList.

package org.kodejava.util;

import java.util.List;
import java.util.LinkedList;
import java.util.ListIterator;

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

        // Retrieves object from LinkedList using the ListIterator
        // interface.
        ListIterator<String> iterator = grades.listIterator();
        while (iterator.hasNext()) {
            System.out.println("Grades: " + iterator.next());
            System.out.println("  hasPrevious  : " + iterator.hasPrevious());
            System.out.println("  hasNext      : " + iterator.hasNext());
            System.out.println("  previousIndex: " + iterator.previousIndex());
            System.out.println("  nextIndex    : " + iterator.nextIndex());
        }
    }
}

The program will print the following output:

Grades: A
  hasPrevious  : true
  hasNext      : true
  previousIndex: 0
  nextIndex    : 1
Grades: B
  hasPrevious  : true
  hasNext      : true
  previousIndex: 1
  nextIndex    : 2
Grades: C
  hasPrevious  : true
  hasNext      : true
  previousIndex: 2
  nextIndex    : 3
Grades: D
  hasPrevious  : true
  hasNext      : true
  previousIndex: 3
  nextIndex    : 4
Grades: E
  hasPrevious  : true
  hasNext      : false
  previousIndex: 4
  nextIndex    : 5

How do I iterate LinkedList elements using Iterator?

By Wayan in Core API, Util Package 0 Comment

This example show you how to use the Iterator interface to iterate elements of a LinkedList.

package org.kodejava.util;

import java.util.List;
import java.util.LinkedList;
import java.util.Iterator;

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

        // Iterates elements in LinkedList using Iterator.
        Iterator<String> iterator = grades.iterator();
        while (iterator.hasNext()) {
            System.out.println("Grade: " + iterator.next());
        }
    }
}

This program prints the following output:

Grade: A
Grade: B
Grade: C
Grade: D
Grade: E

How do I create a LinkedList?

By Wayan in Core API, Util Package 0 Comment

A linked list is a fundamental data structure in programming. It can store data and a references to the next and/or to the previous node. There can be a singly linked list, a doubly linked list and a circularly linked list.

The code below show you how to use the java.util.LinkedList class to create a linked list. In the example we create a LinkedList to store a string object using the add(Object o) method. After create the list we iterate the list and print out the contents.

package org.kodejava.util;

import java.util.List;
import java.util.LinkedList;

public class LinkedListCreate {
    public static void main(String[] args) {
        // Creates a new instance of java.util.LinkedList and
        // adds five string object into the list.
        List<String> grades = new LinkedList<>();
        grades.add("A");
        grades.add("B");
        grades.add("C");
        grades.add("E");
        grades.add("F");

        // Iterates the LinkedList object using the for each
        // statement.
        for (String grade : grades) {
            System.out.println("Grade: " + grade);
        }
    }
}

This program will produce the following output:

Grade: A
Grade: B
Grade: C
Grade: E
Grade: F

How do I add selection listener to JTree?

By Wayan in Swing 0 Comment

This example shows you how to use the TreeSelectionListener to add a tree selection listener to the JTree component. In the listener method below you can see how to get the selected path and print out the selected path to the console.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;
import java.awt.*;

public class JTreeSelectionListenerDemo extends JFrame {

    public JTreeSelectionListenerDemo() throws HeadlessException {
        initializeUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(
                () -> new JTreeSelectionListenerDemo().setVisible(true));
    }

    private void initializeUI() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
        DefaultMutableTreeNode chapterOne = new DefaultMutableTreeNode("Chapter One");
        DefaultMutableTreeNode one = new DefaultMutableTreeNode("1.1");
        DefaultMutableTreeNode two = new DefaultMutableTreeNode("1.2");
        DefaultMutableTreeNode three = new DefaultMutableTreeNode("1.3");

        root.add(chapterOne);
        chapterOne.add(one);
        chapterOne.add(two);
        chapterOne.add(three);

        JTree tree = new JTree(root);
        tree.addTreeSelectionListener(e -> {
            TreePath path = e.getPath();
            int pathCount = path.getPathCount();

            for (int i = 0; i < pathCount; i++) {
                System.out.print(path.getPathComponent(i).toString());
                if (i + 1 != pathCount) {
                    System.out.print(" | ");
                }
            }
            System.out.println();
        });

        JScrollPane pane = new JScrollPane(tree);
        pane.setPreferredSize(new Dimension(200, 400));

        getContentPane().add(pane);
    }
}

How do I change color of selected node in JTree?

By Wayan in Swing 0 Comment

This example show you how to change the color of the selected node of the JTree component. It shows you how to set the node background color, the font color and the selected node border color.

To do this you need to obtain the DefaultTreeCellRenderer object from the JTree instance and modified the selection color of the node.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
import java.awt.*;

public class JTreeTextSelectionColorDemo extends JFrame {
    public JTreeTextSelectionColorDemo() throws HeadlessException {
        initializeUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(
                () -> new JTreeTextSelectionColorDemo().setVisible(true));
    }

    private void initializeUI() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Department");
        DefaultMutableTreeNode book = new DefaultMutableTreeNode("Books");
        DefaultMutableTreeNode fiction = new DefaultMutableTreeNode("Fictions");
        DefaultMutableTreeNode science = new DefaultMutableTreeNode("Sciences");
        DefaultMutableTreeNode text = new DefaultMutableTreeNode("Text Books");
        DefaultMutableTreeNode children = new DefaultMutableTreeNode("Children");

        root.add(book);
        book.add(fiction);
        book.add(science);
        book.add(text);
        book.add(children);

        JTree tree = new JTree(root);

        // Get the DefaultTreeCellRenderer instance of the JTree
        // component. Then we customize the color of the selection
        // node using blue background, white font color and black
        // border.
        DefaultTreeCellRenderer renderer =
                (DefaultTreeCellRenderer) tree.getCellRenderer();
        renderer.setTextSelectionColor(Color.white);
        renderer.setBackgroundSelectionColor(Color.blue);
        renderer.setBorderSelectionColor(Color.red);

        JScrollPane pane = new JScrollPane(tree);
        pane.setPreferredSize(new Dimension(250, 350));

        getContentPane().add(pane);
    }
}
JTree Node Color Demo

JTree Node Color Demo

How do I use a JTree component?

By Wayan in Swing 0 Comment

The example introduce you how to use the JTree swing component to create a presentation of hierarchical data. The hierarchical data can be viewed in expand mode or collapse mode.

To create an item of the tree we create an instance of DefaultMutableTreeNode which located in the javax.swing.tree package. This class implements the TreeNode and MutableTreeNode interfaces. Mutable means that the node can be changed. It can be added new children node or deleted children node from their parent node.

Below we create a tree component to display information about week day names and the month names. The Root node have the Days and Months. The Days node contains a week day names and the Months node contains the month names.

package org.kodejava.swing;

import javax.swing.*;
import javax.swing.tree.DefaultMutableTreeNode;
import java.awt.*;
import java.text.DateFormatSymbols;

public class JTreeDemo extends JFrame {
    public JTreeDemo() {
        initializeUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new JTreeDemo().setVisible(true));
    }

    private void initializeUI() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        // Creating tree node of day names.
        DefaultMutableTreeNode day = new DefaultMutableTreeNode("Days");
        DefaultMutableTreeNode sun = new DefaultMutableTreeNode("Sunday");
        DefaultMutableTreeNode mon = new DefaultMutableTreeNode("Monday");
        DefaultMutableTreeNode tue = new DefaultMutableTreeNode("Tuesday");
        DefaultMutableTreeNode wed = new DefaultMutableTreeNode("Wednesday");
        DefaultMutableTreeNode thu = new DefaultMutableTreeNode("Thursday");
        DefaultMutableTreeNode fri = new DefaultMutableTreeNode("Friday");
        DefaultMutableTreeNode sat = new DefaultMutableTreeNode("Saturday");

        // Adding the day nodes into day tree node.
        day.add(sun);
        day.add(mon);
        day.add(tue);
        day.add(wed);
        day.add(thu);
        day.add(fri);
        day.add(sat);

        // Creates tree node of month names using a for loop where the
        // month names is obtained using the DateFormatSymbols class.
        DefaultMutableTreeNode month = new DefaultMutableTreeNode("Months");
        String[] months = DateFormatSymbols.getInstance().getMonths();
        for (String monthName : months) {
            DefaultMutableTreeNode node = new DefaultMutableTreeNode(monthName);
            month.add(node);
        }

        // Creating a root node for our JTree and add day and month items
        // to the tree.
        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
        root.add(day);
        root.add(month);

        // Creating an instance of JTree using the instance of
        // DefaultMutableTreeNode. We also create a scroll pane for our
        // tree container.
        JTree tree = new JTree(root);
        JScrollPane pane = new JScrollPane(tree);
        pane.setPreferredSize(new Dimension(250, 450));
        getContentPane().add(pane);
    }
}
Swing JTree Demo

Swing JTree Demo

How do I get the remainder of a division?

By Wayan in Basic, Core API 0 Comment

The remainder or modulus operator (%) let you get the remainder of a division of two numbers. This operator can be used to obtain a reminder of an integer or floating point types.

package org.kodejava.basic;

public class RemainderOperatorDemo {
    public static void main(String[] args) {
        int a = 10;
        double b = 49;

        // The reminder operator (%) gives you the remainder of
        // an integer or floating point division operation.
        System.out.println("The result of " + a + " % 5 = " + (a % 5));
        System.out.println("The result of " + b + " % 9.5 = " + (b % 9.5));
    }
}

Here is the result of the program:

The result of 10 % 5 = 0
The result of 49.0 % 9.5 = 1.5

How do I use the ternary operator?

By Wayan in Basic, Core API 0 Comment

The ternary operator or conditional operator can be use as a short version of the if-then-else statement. When you have a simple if-then-else statement in your code that return a value you might use the ternary operator, it can make your code easier to read.

The ternary operator is written using the symbol of ?: and it has the following syntax:

result = testCondition ? value1 : value2;

When the test condition evaluates to true the expression value1 will be returned else the expression value2 will be returned. The value1 or value2 is not only for a simple field or variable, it can be a call to a method for example. But it is advisable to use the ternary operator for a simple thing, because if you over do it, it will make your code harder to read.

Let’s see the following code:

package org.kodejava.basic;

public class TernaryOperatorDemo {
    public static void main(String[] args) {
        int a = 10;
        int b = 20;

        // Get the maximum value
        int min = a < b ? a : b;

        // The use of ternary operator above is an alternative
        // of the following if-then-else statement.
        int minValue;
        if (a < b) {
            minValue = a;
        } else {
            minValue = b;
        }

        // Get the maximum value.
        int max = a > b ? a : b;

        // Get the absolute value.
        int abs = a < 0 ? -a : a;

        System.out.println("min      = " + min);
        System.out.println("minValue = " + minValue);
        System.out.println("max      = " + max);
        System.out.println("abs      = " + abs);
    }
}

The output of the code snippet above:

min      = 10
minValue = 10
max      = 20
abs      = 10

How do I use the continue statement?

By Wayan in Basic, Core API 0 Comment

The continue statement has two forms, the unlabeled and labeled continue statement. The first example shows you how to use the unlabeled continue statement while the second example shows you how to use the labeled continue statement.

package org.kodejava.basic;

public class ContinueDemo {
    public static void main(String[] args) {
        int[] numbers = {5, 11, 3, 9, 12, 15, 4, 7, 6, 17};
        int counter = 0;

        for (int number : numbers) {
            // When number is greater or equals to 10 skip the
            // current loop and continue to the next loop because
            // we only interested to count number less than 10.
            if (number >= 10) {
                continue;
            }

            counter++;
        }

        System.out.println("Found " + counter + " numbers less than 10.");

        // The example below used a labeled continue statement. In the
        // loop below we sum the number in the array until reminder of
        // the number divided by 2 equals to zero. We skip to the next
        // array if the reminder is 0.
        int[][] values = {
                {8, 2, 1},
                {3, 3},
                {3, 4, 5},
                {5, 4},
                {6, 5, 2}};

        int total = 0;

        outer:
        for (int[] value : values) {
            for (int item : value) {
                if (item % 2 == 0) {
                    continue outer;
                }
                total += item;
            }
        }

        System.out.println("Total = " + total);
    }
}

The output of the code snippet:

Found 6 numbers less than 10.
Total = 14

How do I use the break statement?

By Wayan in Basic, Core API 0 Comment

The break statement has two forms, the unlabeled and labeled break. On the example below you see the first example as the unlabeled break. This type of break statement will terminate the innermost loop such as the for, while and do-while loop.

On the second example you’ll see the labeled break. We have two loops, the infinite while and the inner for loop. Using the labeled break we can terminate the outermost loop. In the for loop when the value of y equals to 5 then it will break to the start: label which will continue the program execution to the line after the while loop.

package org.kodejava.basic;

public class BreakDemo {
    public static void main(String[] args) {
        int[] numbers = {5, 3, 6, 9, 8, 7, 4, 2, 1, 10};

        int index;
        boolean found = false;

        int search = 7;
        for (index = 0; index < numbers.length; index++) {
            if (numbers[index] == search) {
                found = true;
                break;
            }
        }

        if (found) {
            System.out.println(search + " found at index " + index);
        } else {
            System.out.println(search + " was not found.");
        }

        start:
        while (true) {
            for (int y = 0; y < 10; y++) {
                System.out.print("y = " + y + "; ");
                if (y == 5) {
                    System.out.println();
                    break start;
                }
            }
        }
    }
}