How to create a queue function in Java

This tutorial is all about how to create a queue function in Java. This function is use to insert and remove and element but in Queue, the element is inserted at the end of the queue and remove the element at the beginning of the queue.

Image: Wikipedia

In creating this program, you need to create a 3 files. Two java class for your java codes and 1 text file for your data. In my case I use the following filenames:

1. QueueBook.Java
2. QueueRun.Java
3. what_Queue.Txt

	import java.io.File;
	import java.util.Scanner;
	import java.util.StringTokenizer;
	/**
	*
	* @author Jillian
	*/
	public class QueueBook {
	/*
	Step 1: create new Book named front and back - LINE 24,25
	Step 2: create a new class named Book - LINE 26, 34
	Step 3: Declare next as new Book - LINE 29
	Step 4: Declare data as new String - LINE 28
	Step 5: Create a new method named Book and includes parameters - LINE 30 TO 33
	*/
	Book front;
	Book back;
	class Book{
	//String name;
	String data;
	Book next;
	Book(String id,String title,String author,String publisher,String year){
	data = id + " | " + title + " | " + author + " | " + publisher + " | " + year;
	next = null;
	}
	}
	/*
	Step 1: Create a string method named enqueue with parameters - LINE 40 TO 53
	Step 2: declare newBook as new Book and initialized it with parameters - LINE 41
	Step 3: declare val as String and initialized it with enqueued--> - LINE 42
	Step 4: create if else statment - line 44 to 52
	Step 5: in if block, initialized the front and back with newBook if isEpty - line 46 to 48
	Step 6: in else block, initialized the front and back with newBook if not Epty - line 51 to 53
	Step 7: return the val value - line 56
	*/
	public String enqueue(String id,String title,String author,String publisher,String year){
	Book newBook = new Book(id,title,author,publisher,year);
	String val = "enqueued--> ";
	if(isEmpty()){
	this.front = newBook;
	this.back = newBook;
	val += newBook.data;
	}else{
	newBook.next = this.back;
	this.back = newBook;
	val += newBook.data;
	}
	return val;
	}
	/*
	Step 1: Create a string method named dequeue with parameters - line 67 to 86
	Step 2: declare frontBook as new Book and initialized it with front - LINE 68
	Step 3: declare val as String and initialized it with dequeued--> - LINE 69
	Step 4: create if else statment - line 71 to 84
	Step 5: in if block, display Noting no records found if empty - line 72
	Step 6: in else if block, initialized the front and back with null if temp is equls to front - line 73 to 77
	Step 7: in else block, create a while loop to check if temp and front is not equal then if true, initialized temp with temp.next
	Step 8: initilized front with temp - line 82
	Step 9: initialized front.next with null - line 85
	Step 10: initialized val variable with frontBook.data - line 87
	Step 11: return val value - line 89
	*/
	public String dequeue(){
	Book frontBook = front;
	String val = "dequeued--> ";
	Book temp = this.back;
	if(isEmpty()){
	val += "Nothing...No records found";
	}else if(temp == front){
	front = null;
	back = null;
	val += frontBook.data;
	}else{
	while(temp.next !=front){
	temp = temp.next;
	}
	front = temp;
	front.next = null;
	val += frontBook.data;
	}
	return val;
	}
	private boolean isEmpty(){
	return this.front == null || this.back==null;
	}
	/*
	Step 1: create a new method named whatThis - line 102
	Step 2: inside the method, declare file as new File and initialized it with a file path - line 103
	Step 3: declare sc as new Scanner and initialized using the file - line 104
	Step 4: create a while loop to check if the scanner element - line 105
	Step 5: inside the loop, create tks as new String tokenizer - line 106
	Step 6: create a while loop to separate the string - line 107 to 118
	*/
	public void whatThis()throws Exception{
	File file = new File("D:\\MIX FILES\\Assorted Files\\DataStructure\\DataStructure2\\DataStucture\\src\\Queues\\what_Queue.txt");
	Scanner sc = new Scanner(file);
	while (sc.hasNextLine()){
	StringTokenizer tks = new StringTokenizer(sc.nextLine(), ",");
	while (tks.hasMoreTokens()){
	String problem = tks.nextToken();
	String implemen = tks.nextToken();
	String subject = tks.nextToken();
	String programmer = tks.nextToken();
	System.out.println("--------------------------------------");
	System.out.println("Problem Domain: " + problem);
	System.out.println("Implementation: " +implemen);
	System.out.println("Subject: " +subject);
	System.out.println("Programmer: " +programmer);
	}
	}
	}
	}

view raw Queue in Java - Queue Book hosted with ❤ by GitHub

	import java.io.File;
	import java.util.Scanner;
	import java.util.StringTokenizer;
	/**
	*
	* @author Jillian
	*/
	public class QueueRun {
	/*
	Step 1: create a main method - line 28 to 45
	Step 2: inside the method, declare file as new File and initialized it with a file path - line 30
	Step 3: declare sc as new Scanner and initialized using the file - line 31
	Step 4: create a while loop to check if the scanner element - line 32
	Step 5: inside the loop, create stl as new String tokenizer - line 33
	Step 6: create a while loop to separate the string - line 34 to 41
	Step 7: display book using dequeue or enqueue - line 43
	Step 8: display book whatThis method - line 44
	*/
	public static void main(String[] args) throws Exception{
	QueueBook Book = new QueueBook();
	File file = new File("D:\\MIX FILES\\Assorted Files\\DataStructure\\DataStructure2\\DataStucture\\src\\DoublyLinkedList2\\bookList.txt");
	Scanner sc = new Scanner(file);
	while (sc.hasNextLine()){
	StringTokenizer st1 = new StringTokenizer(sc.nextLine(), ",");
	while (st1.hasMoreTokens()){
	String callNum = st1.nextToken();
	String title = st1.nextToken();
	String author = st1.nextToken();
	String publisher = st1.nextToken();
	String year = st1.nextToken();
	System.out.println(Book.enqueue(callNum,title,author,publisher,year));
	}
	}
	System.out.println(Book.dequeue());
	Book.whatThis();
	}
	}

view raw Queue in Java - Queue Run hosted with ❤ by GitHub