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

How do I add item at the beginning or the end of LinkedList?

By Wayan in Core API, Util Package 0 Comment

To add an item before the first item in the linked list we use the LinkedList.addFisrt() method and to add an items after the last item in the linked list we use the LinkedList.addLast() method.

package org.kodejava.util;

import java.util.LinkedList;

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

        System.out.println("Original values are:");
        System.out.println("====================");
        for (String grade : grades) {
            System.out.println("Grade = " + grade);
        }

        grades.addFirst("A");
        grades.addLast("F");

        System.out.println("New values are:");
        System.out.println("====================");
        for (String grade : grades) {
            System.out.println("Grade = " + grade);
        }
    }
}

The result of the program are the following:

Original values are:
====================
Grade = B
Grade = C
Grade = D
Grade = E
New values are:
====================
Grade = A
Grade = B
Grade = C
Grade = D
Grade = E
Grade = F

How do I remove the first and last item from LinkedList?

By Wayan in Core API, Util Package 0 Comment

To remove the first or the last elements from the linked list we can use the removeFirst() and removeLast() methods provided by the LinkedList class.

package org.kodejava.util;

import java.util.LinkedList;

public class LinkedListRemoveItems {
    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("Original values are:");
        System.out.println("====================");
        for (String grade : grades) {
            System.out.println("Grade: " + grade);
        }

        grades.removeFirst();
        grades.removeLast();

        System.out.println("New values are:");
        System.out.println("====================");
        for (String grade : grades) {
            System.out.println("Grade: " + grade);
        }
    }
}

This program print out the following result:

Original values are:
====================
Grade: A
Grade: B
Grade: C
Grade: D
Grade: E
Grade: F
New values are:
====================
Grade: B
Grade: C
Grade: D
Grade: E

How do I retrieve particular object from LinkedList?

By Wayan in Core API, Util Package 0 Comment

The example show you how to retrieve particular object from LinkedList using the indexOf() method.

package org.kodejava.util;

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

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

        // Search for Carol using the indexOf method. This method
        // returns the index of the object when found. If not found
        // -1 will be returned.
        int index = names.indexOf("Carol");
        System.out.println("Index = " + index);

        // We can check to see if the index returned is in the range
        // of the LinkedList element size.
        if (index > 0 && index < names.size()) {
            String name = names.get(index);
            System.out.println("Name  = " + name);
        }
    }
}

The program prints the following output:

Index = 2
Name  = Carol

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);
    }
}