How Can I Show My Doubly LinkedList Data in a JTable?

Question

I've been searching for many hours on how to add linked list data to a Jtable but none of the results I found were satisfying. I'm trying to teach myself java so it's a bit difficult for me. Anyways, here is my code. I know it's probably really bad so please be patient with me and help me in making it better.

public class node {

    public node next,pre;
    public String name;
    public double price;

    public node (String n,double p){            
        this (n,p,null,null);
    }

    public node (String n,double p, node ne,node pr){           
        name = n;
        price = p;
        next = ne;
        pre = pr;
    }       
}

---

public class list {

    public node head, tail;

    public list (){         
        head = tail = null;
    }

    public void addHead (String n,double p){            
        if (head != null){              
            head = new node (n,p,head, null);
            head.next.pre = head;
        }           
        else
            head = tail = new node (n,p);
    }

    public int  size (){            
        int size = 0;
        for(node n = head; n.next != null; n = n.next)
          size++;     
          return size;
    }       
    public String print (){
        String s = "";
        if (head !=null){               
            for (node p = head; p !=null; p = p.next)
                return p.name +"\t"+ p.price;                   
        }           
        return s;           
    }
}

---

I don't know what to write in the getValueAt method

import javax.swing.*;
import java.awt.*;
import javax.swing.event.*;
import java.awt.event.*;
import javax.swing.table.*;
class gui extends JFrame implements ActionListener {

    list li = new list ();
    JButton ad;
    JTextField t,t1;
    JTextField t2;
    JTable table  = new JTable (new table_model());

    public gui (){          
        setSize(500,500);
        setTitle("DEMO");
        setLocationRelativeTo(null);
        setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        setLayout(new GridLayout(2,2));
        t = new JTextField ("");
        add(t);
        t1 = new JTextField ("");
        add(t1);
        ad = new JButton ("add");
        ad.addActionListener(this);
        add(ad);
        add(table);
    }

    public class table_model extends AbstractTableModel {
        public list data;
        String [] columns = {"Name","Price",
        };          
        public void addList (list data){                
            this.data = data;
        }
        public int getColumnCount() {
        return columns.length;
        }
        public int getRowCount() {
         return data.size();
        }
           public String getColumnName(int col) {
            return columns[col];
        }

        public Object getValueAt(int row, int col)
        {            

        }
    }

    public void actionPerformed (ActionEvent e){
        if (e.getSource() == ad && !t.equals("")){              
            li.addHead(t.getText(),Integer.parseInt(t1.getText()));         
        }
    }
}

class test{

    public static void main (String [] aed){            
        gui g = new gui();
        g.setVisible (true);            
    }
}

Answer 1

Accessing an element by index in a linked list requires O(n) operations.

JTable needs this kind of access.

A getValueAt for a linked list would look roughly as this: start at the list head, and advance k-1 times to the next entry, then return the resulting value. Obviously, this isn't fast for large data sets.

In other words: don't use a linked list model, but an array-based model, for tables.

Answer 2

I would definitely recommend that you use the LinkedList class from the java.util package instead of implementing your own. If you use Java's LinkedList, then it will have the method T get(int index) which will return the element at the specified index. Then all you have to do is map your objects properties to the correct column.

class MyObj {
    public String name;
    public double price;
}

class MyTableModel extends AbstractTableModel {

    private List<MyObj> contents;

    public MyTableModel(List<MyObj> contents){
        this.contents = contents;
    } 

    @Override
    public int getRowCount(){
        return this.contents.size();
    }

    @Override
    public int getColumnCount(){
        return 2;
    }

    @Override
    public Object getValueAt(int row, int column){
        MyObj myObj = contents.get(row);

        //map column index to property
        return (column == 0)? myObj.name : myObj.price;
    }
}

This does not require a LinkedList specifically. All of the required methods are defined in the List Interface, which the LinkedList class of course implements. If you must use your own LinkedList implementation, then you should also implement the List interface. This will allow your implementation to be used wherever a List is required. Then you will be programming to an interface, not an implementation.