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help with single linked list

 
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help with single linked list
itsjustme82
10 Oct, 2007 - 11:13 PM
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Hi i was given an assignment to write a program to display single linked list using generics.
I am very new to java and want to work on it.

i have a code which should implement it
1) to add an element at the last i tried to work like this but gives me an error saying that "abstract method do not specify a body"
what should i do....?
CODE



public class LinkedList <E> {
    int node;
    
    private LinkedList<E> list;
    public LinkedList (){
        list = null;
        
    }
    public interface List <E> extends Iterable<E> {
        public void add(E obj){
        LinkedList node = new LinkedList(obj);
        LinkedList current;
        
        if(list==null)
            list=node;
        else{
            current = list;
            while  ( current.next !=null)
                current = current.next;
            current.next = node;
        }
        }
        
        Iterator<E> iterator();
            
    }

}      



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1lacca
RE: Help With Single Linked List
11 Oct, 2007 - 01:38 AM
Post #2

code.rascal
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Could you explain what was your intention with the following lines?:
public interface List <E> extends Iterable<E> {
and
Iterator<E> iterator();
?
The second one is generating the error you encounter, and it is because the compiler thinks that it is a function declaration without a function body.
The first line does however something different than what you expect I think.
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itsjustme82
RE: Help With Single Linked List
11 Oct, 2007 - 12:22 PM
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Thanks for writing in..

I have modified the program as below but i have no clue where to start so i thought of starting
1) add elements at the bottom.

I am very new to java and trying to learn .
Thanks for your help.

CODE


import java.util.Iterator;

public interface lList <E> extends Iterable<E> {
    private int data;
    
    /**
     * Add new element to the end of the list.
     * @param obj
     * @postcondition obj is last element of list
     */
    void add(E obj);
    
    /**
     * Attempts to remove value from list.
    
     * @return true if val is an element of the list.
     */
    boolean remove(E val);
    
    /**
     * Test whether parameter is an element of the list.
     * @param obj value for which to test
     * @return true if object is an element of list
     */
    boolean contains(E obj);
    
    /**
     * Test whether list is empty
     * @return true if list has no elements
     */
    boolean isEmpty();
    
    
    int size();
    
    Iterator<E> iterator();
        
}
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1lacca
RE: Help With Single Linked List
11 Oct, 2007 - 10:04 PM
Post #4

code.rascal
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Do you have to declare your own linked list interface?
Java already has a List interface, you could simply implement it with your linked list class. (As a hint: there is also a class called java.util.AbstractList<E> , that takes care most of the boilerplate code)
Apart from this, what you've written seems to be a good start. Now you have to create a class that Implements this interface (I would think about storing the size of the list in a variable, because it is redundant information, and as such can cause problems, but it can be used for optimization as well. Anyway, putting it into the interface as a variable is not a good idea, but if you define it as a method, like size(), then the implementing class can decide how to calculate it - storing in a variable, or counting the data stored every time).
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