链接列表，从文本文件中读取，并按键排序

Question

I'm trying to sort the Linked List by the key( priority number, the int number) from highest to lowest, with the data from text file. I'm stucking at insert the item and sort them. Here is My text file.

Myjob 66

Junk 17

Fun 25

Important 96

Vital 99

MoreFun 28

Work 69

Assignment 44

Here is my Linked List class

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintStream;


@SuppressWarnings("unused")
public class LinkedList {
    Node head;
    Node prev;
    Node cur;
    Node node;

public LinkedList(){

}

public LinkedList(Node head){
    head = null;
}

//getter to get head
public Node gethead(){
    return head;
}

//insert method
public void insert(Data dt){
    try {
        if(head==null){
            head = new Node(dt.getData(), null);
            System.out.println("Opps");
            }
        else if (dt.getData().num > head.dt.num){
            head = new Node(dt.getData(),head);
            System.out.println("Was Here");}
        else if (head.getNext()==null){
            head.setNext(new Node(dt.getData(),null));
            }
        else{
            cur = head.getNext();
            for(prev = head;cur!= null;cur=cur.getNext()){
                if(cur.dt.num>prev.dt.num){
                    Node temp = new Node(dt.getData(),cur);
                    prev.setNext(temp);
                    break;
                }
                else{
                    prev=cur;

                }
            }
        }
    }
        catch (NullPointerException e){
            System.out.println("Here is Error");
        }


}



//Running Linked list
public static void main(String[] args) throws FileNotFoundException{

        LinkedList l1 = new LinkedList();
        Data dt = new Data();

        l1.insert(dt);


}

}

Here is My Node class:

public class Node {
Data dt;
Node next;


public Node(Data dt, Node next){
    this.dt=dt;
    this.next=next;
}


public Node getNext(){
    return next;
}

public void setNext(Node next){
    this.next=next;
}


public Data getData(){
    return dt.getData();
}




}

Here is my Data class:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Data {

protected String name;
protected int num;

public Data(){
}

public Data(String name,int num){
    this.name=name;
    this.num=num;
}

//getter to get Data
@SuppressWarnings("unused")
public Data getData(){
        try{
            int count =0;
            File x = new File("Asg2Data.txt");
            Scanner sc = new Scanner(x);
            while (sc.hasNext()){
                String name = sc.next();
                int num = sc.nextInt();
                Data data= new Data(name,num);
                System.out.println("Name = "+ name+"          "+"Priority = "+num);
                System.out.println(" ");
                count++;
            }
            System.out.println("Total Objects: "+count);
            sc.close();
        }catch(FileNotFoundException e){
            System.out.println("Error");
        }
        return this;
}

//Compare Function
//  public int compare(Data dt){
//      if (this.getData().num > dt.getData().num)
//          return 1;
//      else if (this.getData().num < dt.getData().num)
//          return -1;
//      else
//          return 0;
//  }


// Testing: Worked !!!!!    
    public static void main(String[] args){
        Data d1 = new Data();
        d1.getData();
    }

}

My currently output, when I run from Linked List class:

Name = Myjob          Priority = 66

Name = Junk          Priority = 17

Name = Fun          Priority = 25

Name = Important          Priority = 96

Name = Vital          Priority = 99

Name = MoreFun          Priority = 28

Name = Work          Priority = 69

Name = Assignment          Priority = 44

Total Objects: 8
Opps

My insert method always stop at the first if statement, and never keep going. I have no clue how to fix it. At the mean time, it can not perform the insert the data + sort them by the priority number from highest to lowest. Can anyone help me ? I'm super new in Java. Thank you so much.

-Dustin

Answer 1

First things first your LinkedList is not getting initialized is because in your Data->getData() method you are creating the data objects but never assigning them to the head and the next of the LinkedList head.

As you are new to Java just want to give you some tips on coding with Java.

• Don't use suppress warnings unless utmost important. Most of the time you can handle them.
• Try to segregate the code as much as possible. This will help you and everybody else to understand the code. Ex. why does your Data class have the initialization code, it should be in the LinkedList. Data is just a representation class which will act as a model for your data (This may be design consideration and you might have your reasons to do this..just saying)
• You can also go through the identifiers once and how to use them.

I won't give you the complete the code (because then there will be nothing for you to do) but the below snippet should get you started. I have tried to use your code as much as possible so that it is easier for you to understand. Below code will initialize a LinkedList with the data required, maybe you can take care from there. You can continue to ask any questions if you face any issue going forward

`

 import java.io.File;
 import java.util.Scanner;

 public class LinkedList
    {
        Node head;

        public static void main(String[] args)
        {
            LinkedList list = new LinkedList();
            list.initializeLL();
            list.printLinkedList();
        }

        private void printLinkedList(){
            System.out.println(head);
        }

        private void initializeLL()
        {
            Node currentNode = head;
            try
            {
                File file = new File("Asg2Data.txt");
                Scanner sc = new Scanner(file);
                while (sc.hasNext())
                {
                    Data d = new Data(sc.next(), sc.nextInt());
                    Node n = new Node(d);
                    if(currentNode == null){
                        currentNode = n;
                        head = n;
                    }else{
                        currentNode.setNextNode(n);
                        currentNode = n;
                    }
                }
                sc.close();
            }
            catch (Exception ex)
            {
                ex.printStackTrace();
            }
        }

    }

    class Node
    {

        private Data data;

        private Node nextNode;

        public Node(Data data)
        {
            this.data = data;
        }

        public Data getData()
        {
            return data;
        }

        public void setData(Data data)
        {
            this.data = data;
        }

        public Node getNextNode()
        {
            return nextNode;
        }

        public void setNextNode(Node nextNode)
        {
            this.nextNode = nextNode;
        }

        @Override
        public String toString()
        {
            return "Node [data=" + data + ", nextNode=" + nextNode + "]";
        }



    }

    class Data
    {

        private String name;

        private int data;

        public Data(String name, int data)
        {
            this.name = name;
            this.data = data;
        }

        public String getName()
        {
            return name;
        }

        public void setName(String name)
        {
            this.name = name;
        }

        public int getData()
        {
            return data;
        }

        public void setData(int data)
        {
            this.data = data;
        }

        @Override
        public String toString()
        {
            return "Data [name=" + name + ", data=" + data + "]";
        }
    }

`

Answer 2

Your advices are so awesome. I just fix my code. And it works well now. for now I'm still stucking with the sorting part. I'm doing insertionSort. and here is my code.

public Node insertSort(Node node){
       Node sortedNode = null;
       while(node != null){
        Node current = node;
        node = node.next;
        Node x;
        Node previous = null;
        for(x = sortedNode; x != null; x = x.next){
            if(current.getData().getNum() > x.getData().getNum()){
                    break;
             }
             previous = x;
        }
        if(previous == null){               
              current.next = sortedNode;
              sortedNode = current;
        }
        else{               
           current.next = previous.next;
           previous.next = current;
        }
      }
      return sortedNode; }

My output is

Name = Myjob            Priority=66
Name = Assignment            Priority=44
Name = MoreFun            Priority=28
Name = Fun            Priority=25
Name = Junk            Priority=17
null

they skips whatever greater than 66. Do you have any ideas how to fix this issue, so it can dipslay from 99 down to 17? I rearrange the order in the text file, with the highest first. then It can perform sorting from 99 back to 17 perfectly. But with the original order, my program just perform sorting from 66 to lowest. I don't know why ,and how to fix it? Thank you so much.