LinkedList Java遍历和打印

Question

I would really appreciate if you can help to answer to this question:

I have already created a custom linked list myself in a very standard way using Java. Below are my classes:

public class Node {

   private Object obj;
   private Node next;

   public Node(Object obj){
       this(obj,null);
   }

   public Node(Object obj,Node n){
       this.obj = obj;
       next = n;
   }

   public void setData(Object obj){
       this.obj = obj;
   }

   public void setNext(Node n){
       next = n;
   }

   public Object getData(){
       return obj;
   }

   public Node getNext(){
       return next;
   }

}




public class linkedList {
    private Node head;


    public linkedList(){
        head = null;
    }

    public void setHead(Node n){
        head = n;
    }

    public Node getHead(){
        return head;
    }


   public void add(Object obj){
       if(getHead() == null){
           Node tmp = new Node(obj);
           tmp.setNext(getHead());
           setHead(tmp);
       }else{
           add(getHead(),obj);
       }
   }


   private void add(Node cur,Object obj){
       if(cur.getNext() == null){
           Node tmp = new Node(obj);
           tmp.setNext(cur.getNext());
           cur.setNext(tmp);
       }else{
           add(cur.getNext(),obj);
       }
   }


}

Im trying to print value i have inserted into the list as below

public static void main(String[] args) {
        // TODO code application logic here
        Node l = new Node("ant");
        Node rat = new Node("rat");
        Node bat = new Node("bat");
        Node hrs = new Node("hrs");

        linkedList lst = new linkedList();
        lst.add(l);
        lst.add(rat);
        lst.add(bat);
        lst.add(hrs);



        Node tmp = lst.getHead();
        while(tmp != null){

            System.out.println(tmp.getData());
            tmp = tmp.getNext();

        }


    }

but the output i got from the IDE is

linklist.Node@137bd6a1
linklist.Node@2747ee05
linklist.Node@635b9e68
linklist.Node@13fcf0ce

why does it print out the reference but not the actual value of the string such as bat,ant,rat... ?

If i want to print out the actual value then what should i do?

Thank you very much

Answer 1

Your linkedList class already creates the Node s for you!

linkedList list = new linkedList();
list.add("foo");
list.add("bar");
Node tmp = lst.getHead();
while(tmp != null){
    System.out.println(tmp.getData());
    tmp = tmp.getNext();
}

Will print

foo
bar

Answer 2

You need to override the toString() method on Node :

@Override
String toString() {
  String val = // however you want to represent your Node
  return val;
}

and print the node:

System.out.println(tmp);

Alternatively, have Node.getData() return a String if you know you are only going to store String s -- change the Object s to String in the Node definition

Alternatively, you could use generics to specify the type of data inside the node

UPDATE: after a little more thought (provoked by comments), I see something amiss:

tmp.getData() should return a string (based on Node's single parameter ctor and that you are passing strings), but the output is about references to Node objects. Is it possible that linkedList.add re-sets the Node 's obj member to a Node instead?

Answer 3

The LinkedList is of Objects, Objects toString method prints out the reference. If you want to print out the string you are going to have either change the LinkedList to a String/Generics or cast the print out like this:

String output = (String)tmp.getData();
System.out.println(output);

(you can do this in one line if you want).

Answer 4

Your getData() in Node class returns an Object type. You need to cast it into a String so that it gets printed by println() properly.

System.out.println((String)tmp.getData());

should do the trick for you.