Printing out a linked list using toString

Question

Ok guys  so I am trying to learn how to print out a linked list   I have all the methods that I would need to use for the list  but I can t figure out how to display the values of the nodes   Right now there is nothing in my main method because I kept getting errors trying to call non static methods in the main   I have a toString method that displays the contents of the list   How would I go about calling this toString to display the value of each node   Any advice will be greatly appreciated   Here is the node class   public class LinkedListNode        private int data      private LinkedListNode next        public LinkedListNode int data                this data   data          this next   null             public int getData                 return data             public void setData int d                data   d             public LinkedListNode getNext                 return next             public void setNext LinkedListNode n                next   n            Here is the LinkedList class that contains the main and methods to manipulate the list   public class LinkedList        public LinkedListNode head       public static void main String   args         LinkedList l   new LinkedList        l insertFront 0       System out println l toString                 public LinkedList             this head   null             public int removeFront            if head    null               System out println  Error - Attempting to call removeFront   on empty list                return 0           else              int temp   head getData                head   head getNext                  return temp                        public void insertFront int data           if head    null               head   new LinkedListNode data            else              LinkedListNode newNode   new LinkedListNode data               newNode setNext head               head   newNode                              public void insertBack int data           if head    null               head   new LinkedListNode data            else              LinkedListNode newNode   new LinkedListNode data               LinkedListNode current   head              while current getNext      null                   current   current getNext                              current setNext newNode                               public int removeBack            if head    null               System out println  Error - Attempting to call removeBack   on empty list                return 0           else if  head getNext      null               int temp   head getData                head   null              return temp           else               LinkedListNode current   head              while current getNext   getNext      null                   current   current getNext                              int temp   current getNext   getData                current setNext null               return temp                              public String toString            String retStr    Contents  n            LinkedListNode current   head          while current    null               retStr    current getData       n               current   current getNext                        return retStr             public LinkedListNode getHead             return head             public void setHead LinkedListNode head            this head   head

User · Answer

As has been pointed out in some other answers and comments, what you are missing here is a call to the JVM System class to print out the string generated by your toString() method.

LinkedList myLinkedList = new LinkedList();
System.out.println(myLinkedList.toString());

This will get the job done, but I wouldn't recommend doing it that way. If we take a look at the javadocs for the Object class, we find this description for toString():

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The emphasis added there is my own. You are creating a string that contains the entire state of the linked list, which somebody using your class is probably not expecting. I would recommend the following changes:

Add a toString() method to your LinkedListNode class.
Update the toString() method in your LinkedList class to be more concise.
Add a new method called printList() to your LinkedList class that does what you are currently expecting toString() to do.

In LinkedListNode:

public String toString(){
   return "LinkedListNode with data: " + getData();
}

In LinkedList:

public int size(){
    int currentSize = 0;
    LinkedListNode current = head;
    while(current != null){
        currentSize = currentSize + 1;
        current = current.getNext();
    }

    return currentSize;
}

public String toString(){
    return "LinkedList with " + size() + "elements.";
}

public void printList(){
    System.out.println("Contents of " + toString());

    LinkedListNode current = head;
    while(current != null){
        System.out.println(current.toString());
        current = current.getNext();
    }

}

User · Answer

When the JVM tries to run your application  it calls your main method statically  something like this   LinkedList main      That means there is no instance of your LinkedList class  In order to call your toString   method  you can create a new instance of your LinkedList class   So the body of your main method should be like this   public static void main String   args          creating an instance of LinkedList class     LinkedList ll   new LinkedList            adding some data to the list     ll insertFront 1       ll insertFront 2       ll insertFront 3       ll insertBack 4        System out println ll toString

User · Answer

I do it the following way   public static void main String   args         LinkedList list   new LinkedList        list insertFront 1       list insertFront 2       list insertFront 3       System out println list toString        String toString         StringBuilder result   new StringBuilder        for Object item this            result append item toString             result append   n      optional           return result toString

User · Answer

public static void main String   args         LinkedList list   new LinkedList        list insertFront 1       list insertFront 2       list insertFront 3       System out println list toString        String toString                 String result                   LinkedListNode current   head              while current getNext      null                   result    current getData                    if current getNext      null                        result                                            current   current getNext                              return  List      result

User · Answer

A very simple solution is to override the toString   method in the Node  Then  you can call print by passing LinkedList s head  You don t need to implement any kind of loop     Code     public class LinkedListNode                  New      Override     public String toString             return String format  Node  d  next    s    data  next              public class LinkedList        public static void main String   args             LinkedList l   new LinkedList            l insertFront 0           l insertFront 1           l insertFront 2           l insertFront 3              New         System out println l head

[java] Printing out a linked list using toString

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