I am trying to solve a linked list coding challenge in python. And I have given only following class to create a linked list # Definition for singly-linked list. class ListNode(object): def More on stackoverflow.com

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I create a linked list using python class. But I can't manipulate the output format: class Node: def __init__(self, item=None): self.item = item self.next = None class LinkedL... More on stackoverflow.com

I will now use meaningful names for classes if you don't mind, so it makes more sense. First of all,we need to start with creating a single link, or a Node (or your "DEF" object). public class Node { Date data; // the payload, which will be a single date entry from the text file Node next; //pointer to the next link in chain Node prev; //pointer to the previous link in chain public Node(Date date) { //a constructor that takes a Date value as parameter and stores it in a link, pointing to nothing this.data = date; this.next = null; this.prev = null; } } A doubly-linked list will maintain a chain of Nodes and keep track of its size: class MyLinkedList { int size; Node head; //we need to know where to start from, so we keep a reference to the first link Node tail; //pointer to the end of the list //..other methods, including addNode(), removeNode(), //get(index), isEmpty(), etc. } The assignment requires to keep two sentinel nodes as well - i.e. empty head and tail nodes. Sentinels contain no payload (no data) and are pointing to nulls, just so we can safely reach the end of the list and avoid a NullPointerException. I don't want to do your entire homework for you, so I recommend you read up on doubly linked list implementation with sentinel nodes in your textbook/lecture notes. If you don't have any for some reason, here's a quick reference you can use or just google "java doubly linked list implementation example" anywhere. Next, you're gonna tie it all together - read text from a file line by line, extract each date, wrap it in a single Node and add the Node to the linked list. To read data from a file, google "java Scanner" examples, it's fairly easy. Then depending on the file's format, you will need to figure out how to extract a single date from a line of input. But the lines you read are of type String (or simple text). In my example I'm assuming thre's no more data in a single line but a single date in plain text format. To convert a String to a valid Date (not sure if required, but you mentioned error checks so I'm assuming it is) you might want to use the DateFormat.parse(String) method and handle the ParseException as your prof's heart desires. Here's how it should go in a nutshell: public class ABC { String myFile; public ABC(String myFile) { this.myFile = myFile; } The reason I don't put the input code inside the constructor is that it's considered a bad practice. Constructors should return very fast and avoid using methods that can throw IO exceptions - in this particular case at least (until you learn about finalizers and such)/ Instead, I took the input out to the separate method doInput() which will return a ready-made LinkedList made of your text file data: public MyLinkedLIst doInput() { //use Scanner to read from myFile, convert each line to a Date //and wrap it in a Node: Scanner myScanner = null; try { myScanner = //instantiate a Scanner object here with //the passed file name (myFile) MyLinkedList myList = new MyLinkedList(); while (myScanner.hasNextLine()) { String line = //read next line from the scanner try { Date myDate = DateFormat.parse(line.trim()); Node node = //wrap myDate in a Node instance myList.add(node); catch (ParseException e) { System.out.println("Could not parse line " + line); } catch (IOException e) { System.out.println("ERROR: Could not open file " + myFile); } } Then in a main() method somewhere, be it your ABC class, or somewhere else, you will instantiate an object of type ABC with your textfile name as a single argument, and call doInput() on it to receive a linked list of dates to do with as you please. All you have to do now is implement the MyLinkedList class as mentioned above. (and then display it with JFrame but that part I hope you can handle yourself'). More on reddit.com