Java Interfaces vs. Abstract class

Summary of the similarities and differences between the Interfaces and Abstract class

	Abstract class	Interface
Has a constructor	Yes	No
An instance can be created from it	No	No
Implemented as part of the Class Hierarchy. Uses Inheritance	Yes (In extendes clause)	No (In implements clause)
records and enums can extend or implement?	No	Yes
Inherits from java.lang.Object	Yes	No
Can have both abstract methods and concrete methods	Yes	Yes (as of JDK 8)
Abstract methods must include abstract modifier	Yes	No (Implicit)
Supports default modifier for it's methods	No	Yes (as of JDK 8)
Can have instance fields (non-static instance fields)	Yes	No
Can have static fields (class fields)	Yes	Yes - (implicitly public static final)

Java - Data Structures - non linear - Binary Tree from the scratch

 

package datastructures.linear;

public class TreeFromTheScratch {
    public static void main(String[] args) {
        TreeImpl tree = new TreeImpl();
        tree.insert(10);
        tree.insert(5);
        tree.insert(15);
        tree.insert(6);
        tree.insert(1);
        tree.insert(8);
        tree.insert(12);

        System.out.println(("6 "+(tree.find(6)?"Found":"Not Found")));
        System.out.println(("7 "+(tree.find(7)?"Found":"Not Found")));
    }
}

class TreeImpl{
    private Node root;

    public void insert(int value){
        var newNode = new Node(value);
        if(null==root){
            root = newNode;
            return;
        }
        var current= root;
        while(true){
            if(current.value>value){
                if(current.leftChild==null){
                    current.leftChild = newNode;
                    break;
                }
                current = current.leftChild;
            } else {
                if(current.rightChild==null){
                    current.rightChild = newNode;
                    break;
                }
                current = current.rightChild;
            }
        }
    }

    public boolean find(int value){
        var current = root;
        while (current!=null){
            if(current.value==value){
                return true;
            } else if(current.value>value){
                current = current.leftChild;
            } else {
                current = current.rightChild;
            }
        }
        return false;
    }

    private class Node{
        private int value;
        private Node leftChild;
        private Node rightChild;

        public Node(int value) {
            this.value = value;
        }

        @Override
        public String toString() {
            return "Node{" +
                    "value=" + value +
                    ", leftChild=" + ((null!=leftChild)?leftChild.value:"null") +
                    ", rightChild=" + ((null!=rightChild)?rightChild.value:"null") +
                    '}';
        }
    }
}

 

Java - Data Structures - Creating HashMap using array and LinkedLists

Collision Resolved by Using Changing Technique

 

package datastructures.linear;

import java.util.LinkedList;

public class HashMapFromArray {
    public static void main(String[] args) {
        HashMapArray obj = new HashMapArray();

        obj.put(0, "Data 1");
        obj.put(3,"Data 3");
        obj.put(13,"Data 13");
        obj.put(23,"Data 23");
        obj.put(43,"Data 43");
        obj.put(2352,"Data 2352");
        obj.put(972,"Data 972");

        obj.get(0);
        obj.get(3);
        obj.get(13);
        obj.remove(3);
        obj.get(3);
        obj.get(13);
        obj.get(2352);

        //obj.display();
    }
}

class HashMapArray {
    private LinkedList<Entry>[] hashmap = new LinkedList[10];

    public void put(int key, String value) {
        var newKey = getHash(key);

        //If there are no data in the index,initiate new list
        if (null == hashmap[newKey])
            hashmap[newKey] = new LinkedList<Entry>();

        //If the Item already existing in the list,replace the value
        for (var entry: hashmap[newKey])
            if(entry.key==key){
                entry.value = value;
                return;
            }

        //If item not in the array,add value as a new item
        hashmap[newKey].addLast(new Entry(key, value));
    }

    public void get(int key) {
        var newKey = getHash(key);
        var currentData = hashmap[newKey];
        boolean flag = false;
        if (null == currentData)
            throw new IllegalArgumentException();
        else
            for (var dataObj : currentData)
                if(dataObj.key==key) {
                    System.out.println(dataObj.value);
                    flag = true;
                    break;
                }
        System.err.println((!flag)?key+" - Not Fond":"");
    }

    public void remove(int key){
        var newKey = getHash(key);
        var currentData = hashmap[newKey];
        boolean flag = false;
        if (null == currentData)
            throw new IllegalArgumentException();
        else
            for (var dataObj : currentData)
                if(dataObj.key==key) {
                    currentData.remove(dataObj);
                    System.out.println("Done");
                    flag = true;
                    break;
                }
        System.err.println((!flag)?"Error":"");
    }

    private int getHash(int key) {
        return (key >= hashmap.length) ? key % hashmap.length : key;
    }

    public void display() {
        System.out.println(hashmap);
    }

    private class Entry {
        private int key;
        private String value;

        Entry(int key, String value) {
            this.key = key;
            this.value = value;
        }
    }
}

 GitHub Url

Java - Data Structures - LinkedList Example

package datastructures.linear;

import java.util.*;
import java.util.stream.Collectors;

public class LinkListExample {
    public static void main(String[] arg){
        LinkedList<Integer> ll = new LinkedList<Integer>();

        for (int i=0;i<10;i++)
        //Adding data
        ll.add((int) Math.round(Math.random()*100));

        System.out.println("Initial LinkedList " + ll);

        ll.set(1, 55);
        System.out.println("Updated LinkedList " + ll);

        ll.add(1, 66);
        System.out.println("Updated LinkedList " + ll);

        ll.addFirst(11);
        ll.addLast(99);
        System.out.println("After Adding the first and Last Element" + ll);

        ll.remove(3);
        System.out.println("After the Index Removal " + ll);

        ll.remove("99");
        System.out.println("After the Object Removal " + ll);

        //Removing first and last element from the array
        ll.removeFirst();
        ll.removeLast();
        System.out.println("After Adding the first and Last Element" + ll);

        //Searching Item in the Array
        System.out.println(((ll.contains(45))?"45 found":"45 not found"));

        //Iterate linklist
        //using for loop
        for (int j=0;j<ll.size();j++)
            System.out.print(ll.get(j)+",");
        System.out.println();
        //Using Iterator
        Iterator it = ll.iterator();
        while (it.hasNext())
            System.out.print(it.next()+",");
    }
}

Java - Logics - Palindrome word Checker

package logics.words;

import java.util.ArrayList;
import java.util.NoSuchElementException;
import java.util.Scanner;
import java.util.stream.Collectors;

public class PalindromeWordsChecker {
    public static void main(String[] arg){
        Scanner scanner = new Scanner(System.in);
        boolean flag = true;
        ArrayList<Character> wordCheck;
        int count;
        String scan = "";
        do {
            System.out.println();
            System.out.print("Enter Word : ");
            try {
                scan = scanner.nextLine().toLowerCase();
            } catch (Exception e){
                scan = null;
                System.err.println("Error in read Line :"+e.getMessage());
            }
            if(scan.isEmpty()||scan.length()<2||scan.isBlank()) continue;
            flag = true;
            wordCheck = new ArrayList<>(
                    scan.chars()
                            .mapToObj(e -> (char) e)
                            .collect(Collectors.toList()));
            count = wordCheck.size()-1;
            for (int i = 0;i<wordCheck.size()/2;i++){
                if(wordCheck.get(i) !=wordCheck.get(count)){
                    flag = false;
                    break;
                }
                count--;
            }
            if(flag){
                System.out.println(scan+" is palindrome word");
            } else {
                System.err.println(scan+" is NOT palindrome word");
            }
        } while(!scanner.equals("q"));
    }
}

GitHub Link

Java - Data Structures - Queue Example

 Elements are processed in the First In First Out (FIFO) manner

Those Queues that are present in the util package are known as Unbounded Queues.

Those Queues that are present in the util. concurrent packages are known as bounded Queues.

Since Queue is an interface, It requires a concrete class for the declaration.

The most common classes are the LinkedList, PriorityQueue, ArrayBlockingQueue, and ArrayDeque

Methods of Java Queue Interface

Method	Description
boolean add(object)	It is used to insert the specified element into this queue and return true upon success.
boolean offer(object)	It is used to insert the specified element into this queue.
Object remove()	It is used to retrieve and removes the head of this queue.
Object poll()	It is used to retrieve and remove the head of this queue or returns null if this queue is empty.
Object element()	It is used to retrieve but does not remove, the head of this queue.
Object peek()	It is used to retrieve, but does not remove, the head of this queue, or returns null if it is empty.

Code Example

package datastructures.linear;

import java.util.*;

public class QueueExample {

    public static void main(String[] arg){

        /*
        Since Queue is an interface, It requires a concrete class for the declaration.
        The most common classes are the LinkedList and PriorityQueue and ArrayDeque
        Methods of Java Queue Interface

        * boolean add(object)
            - It is used to insert the specified element into this queue and return true upon success.
        * boolean offer(object)
            - It is used to insert the specified element into this queue.
        * Object remove()
            - It is used to retrieves and removes the head of this queue.
        * Object poll()
            - It is used to retrieves and removes the head of this queue, or returns null if this queue is empty.
        * Object element()
            - It is used to retrieves, but does not remove, the head of this queue.
        * Object peek()
            - It is used to retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
         */

        //Queue implementation Using One Dimensional Array
        OneDimensionalArrayAsAQueue qu1 = new OneDimensionalArrayAsAQueue(5);
        qu1.runQueue();

        QueueExampleRun pq = new QueueExampleRun(new PriorityQueue<>());
        pq.runQueue();
        QueueExampleRun ad = new QueueExampleRun(new ArrayDeque<>());
        ad.runQueue();
        QueueExampleRun ll = new QueueExampleRun(new LinkedList<>());
        ll.runQueue();
    }
}

class QueueExampleRun extends CommonMethods{

    QueueExampleRun(Queue<Integer> queue) {
        super(queue);
    }

    public void runQueue(){
        addData();
        displayData();
        Scanner scanner = new Scanner(System.in);
        int val = 0;
        do {
            System.out.println();
            System.out.print("Enter Value : ");
            val = scanner.nextInt();
            addSingleItemToQueue(val);
            displayData();
        } while (val!=99);

        int exit = 1;
        do {
            exit = scanner.nextInt();
            removeItemFromQueue();
            // displayData();
        } while(exit!=0);
    }
}

class OneDimensionalArrayAsAQueue{
    int startPointer,endPointer;
    int queueSize;
    static int[] q1;

    OneDimensionalArrayAsAQueue(){
        startPointer = 0;
        endPointer = 0;
        queueSize = 5;
    }

    OneDimensionalArrayAsAQueue(int size){
        queueSize = size;
        q1 = new int[queueSize];
    }

    void runQueue(){
        for (int i=0;i<5;i++)
            enQueue((int) Math.round(Math.random()*100));
        display();
        deQueue();
        display();
        deQueue();
        display();
        deQueue();
        display();
        deQueue();
        display();
        deQueue();
        display();
        deQueue();
    }

    /*
    Used for insert Data
    Logic - if it isn't full ( array size = endPointer ),
    insert data to the array and increase pointer by 1
     */
    void enQueue(int value){
        if(queueSize==endPointer){
            System.out.println("Queue is full");
        } else {
            q1[startPointer] = value;
            startPointer++;
        }
    }

    /*
    Used for remove Item from the Queue
    Since Queue are FIFO( First In First Out ), Removing should start from the begging of the array
    All other items should shifted to 1 position up
     */
    void deQueue(){
        if(startPointer==0){
            System.out.println("Queue is empty");
        } else {
            for (int i=0;i<startPointer-1;i++)
                q1[i] = q1[i+1];
            startPointer--;
        }
    }

    void display(){
        if(startPointer==0){
            System.out.println("Queue is empty");
        } else {
            System.out.println();
            for (int i=0;i<startPointer;i++) {
                System.out.println(q1[i]);
            }
        }
    }
}

abstract class CommonMethods{
    Queue<Integer> queue;

    CommonMethods(Queue<Integer> queue){
        this.queue = queue;
    }

    public void addData(){
        //Adding Data to Queue
        for (int i=0;i<5;i++)
            queue.add(((int) Math.round(Math.random()*100)));
    }

    public void removeItemFromQueue(){
        System.out.println("Removing Item using remove = "+queue.remove());

        System.out.println("Removing Item using poll = "+queue.poll());
    }

    public void viewTopItemInQueue(){
        System.out.println("View top item using element = "+queue.element());

        System.out.println("View top item using peek = "+queue.peek());
    }

    public void addSingleItemToQueue(int value){
        //Add Item to Queue
        if(queue.add(value)) System.out.println("Added Item to Queue using Add method "); else System.out.println("Error in Adding Data to Queue");

        //Add data using offer method
        if(queue.offer(value)) System.out.println("Added Item to Queue using offer method"); else System.out.println("Error in Adding Data to Queue");
    }

    public void displayData(){
        System.out.println();
        System.out.println("Queue Size: " + queue.size());

        System.out.println("Queue is empty: " + queue.isEmpty());

        System.out.println("----------------------------------------------------");
        System.out.println("Display Data using Iterator");
        Iterator<Integer> iterator = queue.iterator();
        while(iterator.hasNext()) System.out.println(iterator.next());
        System.out.println("----------------------------------------------------");
        System.out.println();
        System.out.println("----------------------------------------------------");
        System.out.println("Display Data using for");
        for (Integer queueItem : queue) System.out.println(queueItem);
        System.out.println("----------------------------------------------------");
    }
}

GitHub Link

Java - Data Structures - Stack Example

package datastructures.linear;

import java.util.EmptyStackException;
import java.util.Iterator;
import java.util.Stack;

public class StackExample {
    public static void main(String[] arg){
        StackImplementation obj  = new StackImplementation();
        obj.addData();
        obj.displayData();
        obj.operations();
    }
}

class StackImplementation{
    // Creating an empty Stack
    Stack stackObj;
    //Creating Integer stack
    Stack<Integer> stackSpecificObj = new Stack<>();

    public StackImplementation(){
        stackObj = new Stack();
    }

    public void addData(){
        //without specifying data type, we can store any type of Data
        stackObj.push(5);
        stackObj.push("Hello");
        stackObj.push(10.5);
        stackObj.push(45);
        System.out.println(stackObj);

        stackSpecificObj.push(12);
        stackSpecificObj.push(67);
    }

    public void operations(){
        /*
        there are five operations
        -------------------------------------------------------------------------------------------------
        |Method       |Modifier and Type    | Method Description                                        |
        |-----------------------------------------------------------------------------------------------|
        |empty()      |boolean              | checks the stack is empty or not                          |
        |push(E Item) |E                    | insert an element on to the top of the stack              |
        |pop()        |E                    | return top of the stack ( removed item from the stack )   |
        |peek()       |E                    | return top of the stack ( without removing )              |
        |search(Obj)  |int                  | Search and return the position                            |
        -------------------------------------------------------------------------------------------------
         */
        emptyCheck();
        insertData(15);
        displayData();
        popData();
        displayData();
        peekData();
        displayData();
        searchData(67);
        insertData(11);
        insertData(61);
        insertData(7);
        sortStack();
        displayData();

        iterateStack();
        displayData();
        popAllData();
        displayData();
        popData();
        displayData();
        peekData();
    }

    public void searchData(int value){
        System.out.println("---------search() Operation ="+value+"------------");
        System.out.println(stackSpecificObj.search(value));
    }

    public void peekData(){
        try {
            System.out.println("---------peek() Operation------------");
            System.out.println(stackSpecificObj.peek());
        } catch (EmptyStackException e){
            System.err.println("No more Data to peek");
        }
    }

    public void popData(){
        try {
            System.out.println("---------pop() Operation------------");
            System.out.println(stackSpecificObj.pop());
        } catch (EmptyStackException e){
            System.err.println("No more Data to pop");
        }
    }

    public void insertData(int value){
        System.out.println("---------insert(object) Operation------------");
        stackSpecificObj.push(value);
    }

    public void emptyCheck(){
        System.out.println("---------empty() Operation------------");
        if(stackSpecificObj.empty()){
            System.out.println("Stack is Empty");
        } else {
            System.out.println("Stack isn't Empty");
        }
    }

    public void sortStack(){
        System.out.println("---------sort() Operation------------");
        stackSpecificObj.sort(null);
    }

    public void displayData(){
        System.out.println("---------Display Stack------------");
        System.out.println(stackSpecificObj);
    }

    public void iterateStack(){
        System.out.println("---------Iterate Stack------------");
        Iterator it = stackSpecificObj.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }

    public void popAllData(){
        System.out.println("---------pop() Operation for all------------");
        while(!stackSpecificObj.empty()){
            System.out.println(stackSpecificObj.pop());
        }
    }
}

Github Link

Java - Data Structures - Multi dimensional Arrays Example

package datastructures.linear;

class MultidimensionalArrays {
    public static void main(String[] arg) {
        System.out.println("Two Dimensional datastructures.linear.Array Example");
        System.out.println("_____________________________");
        TwoDimensionalArray obj = new TwoDimensionalArray();
        obj.displayArray();
        System.out.println("");
        System.out.println("Three Dimensional datastructures.linear.Array Example");
        System.out.println("_____________________________");
        ThreeDimensionalArray objt = new ThreeDimensionalArray();
        objt.displayArray();
    }
}


class TwoDimensionalArray{
    //Declaration an array
    private int[][] intArray;

    public TwoDimensionalArray(){
        //Initializing an array
        intArray = new int[][]{{11,24,36,42,58},{45,67,23,45,23},{29,64,73,40,71},{44,66,87,43,95},{34,72,93,37,89}};
    }

    public void displayArray(){
        for(int i=0;i<intArray.length;i++){
            for(int j=0;j<intArray[i].length;j++)
                System.out.print("["+i+"]["+j+"]'"+intArray[i][j]+"' ");
            System.out.println("");    
        }        
    }
}

class ThreeDimensionalArray{
    //Declaration an array
    private long[][][] intArray = new long[5][5][5];

    public void assignValues(){
        //Initializing an array with random values
        for(int i=0;i<5;i++)
            for(int j=0;j<5;j++)
                for(int k=0;k<5;k++)
                    intArray[i][j][k] = Math.round(Math.random()*100);
    }

    public void displayArray(){
        this.assignValues();
        for(int i=0;i<5;i++){
            for(int j=0;j<5;j++){
                for(int k=0;k<5;k++)
                    System.out.print("["+i+"]["+j+"]["+k+"]'"+intArray[i][j][k]+"' ");
                System.out.println("");    
            } 
            System.out.println("");
        }       
    }

}

GitHub Link