java中的链表教程

Question

i am learning linked list in Java and wrote some sample code for practise. Basically its a singe linked list. The code works fine but it reverses the output. That is it prints out cory, joe and tom and i want the output to be tom, joe and cory. Tom being the first node. How do i go about that or is that the way a single linked list works. That is it always reverses the output?

public class LinkedList {
public String name;
public LinkedList next;
public LinkedList(String name)
{
  this.name = name;
  this.next = null;
}
public String toString()
{
  return name;
}
public static void main(String[] args) {
    // TODO Auto-generated method stub
      Linked l = new Linked();
      l.insert("tom");
      l.insert("joe");
      l.insert("cory");
      l.print();

    }
 }
class Linked
{
LinkedList first;

public Linked()//initialize 
{
    this.first = null;
}

public void insert(String name)
{    
    LinkedList g = new LinkedList(name);
    g.next = first;
    first = g;  
}
 //checks if the list is empty
public boolean isEmpty()
{
    return (first ==null);
}
public void print() //displays the list
 {
    LinkedList t = first;
    while(t!=null)
    {
        System.out.println(t);
        t = t.next;
    }
  }
}

Answer 1

You are inserting at beginning of LinkedList. If you want to add then insert new node after last node. You would need a tail reference.

public String name;
    public LinkedList next;
    public LinkedList(String name)
    {
      this.name = name;
      this.next = null;
    }
    public String toString()
    {
      return name;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
          Linked l = new Linked();
          l.insert("tom");
          l.insert("joe");
          l.insert("cory");
          l.print();

        }
     }
    class Linked
    {
    LinkedList first;
    LinkedList tail;

    public Linked()//initialize 
    {
        this.first = null;
        this.tail = first;
    }

    public void insert(String name)
    {    
        LinkedList g = new Test(name);
        if(isEmpty())
        {
            first = g;
            tail = first;
        }
        else
        {
            tail.next = g;
            tail = g;
        } 
    }
     //checks if the list is empty
    public boolean isEmpty()
    {
        return (first ==null);
    }
    public void print() //displays the list
     {
        LinkedList t = first;
        while(t!=null)
        {
            System.out.println(t);
            t = t.next;
        }
}

If you notice I added a tail reference and instead of inserting the new object at the beginning i attach it to the end of the LinkedList. You could change the method name to add. In fact you could have 2 methods keep yours how it is...then add my new method insert but call it add that way you could insert at beginning or add to end of LinkedList.

Answer 2

As @brso05 pointed out, you are inserting values to head, instead of to the tail.

That is

tom
joe -> tom
cory -> joe -> tom

instead you should insert it to the tail, like this

public void insert(String name)
{ 
  if(first==null) 
  {
        LinkedList g = new LinkedList(name);
        g.next = null;
        first = g;  
  } else {

        LinkedList g = new LinkedList(name);

        if (first.next==null) {
          g.next = null;
          first = g;  
          return;
        }

        LinkedList l=first.next;
        for(;l!=null;l=l.next){
         if(l.next==null) {
           l.next = g;
           g.next = null;  
           break;
         }
        }


  }

}

This is not a very good solution, it should be improvised