trying to implement concept of LinkedList through java , but it is giving giving error at compile time?

Question

I am trying simple linked list Collection program, but it is not giving me out put.
i created this stuff

import java.lang.*;  
import java.util.*;  

cla         


        

Answer 1

Use

LinkedList<Integer> ll = new LinkedList<Integer>();
Iterator<Integer> itr = ll.iterator();
ListIterator<Integer> litr = ll.listIterator();

Insted of

LinkedList ll = new LinkedList();
Iterator itr = ll.iterator();
ListIterator litr = ll.listIterator();

As shown below

    LinkedList<Integer> ll = new LinkedList<Integer>();
    System.out.println("CONTENTS OF l1 = " + ll);
    System.out.println("SIZE = " + ll.size());
    ll.add(new Integer(10));
    ll.add(new Integer(20));
    ll.add(new Integer(30));
    ll.add(new Integer(40));
    System.out.println("CONTENTS OF ll = " + ll);
    System.out.println("SIZE = " + ll.size());
    // retrieving data of ll using toArray ()
    Object obj[] = ll.toArray();
    int s = 0;
    for (int i = 0; i < obj.length; i++) {
        Integer io = (Integer) obj[i];
        int x = io.intValue();
        s = s + x;
    }
    System.out.println("SUM USING toArray () = " + s);
    ll.addFirst(new Integer(5));
    ll.addFirst(new Integer(6));
    System.out.println("CONTENTS OF ll = " + ll);
    System.out.println("SIZE = " + ll.size());
    // retrieving data of ll using iterator ()
    Iterator<Integer> itr = ll.iterator();
    int s1 = 0;
    while (itr.hasNext()) {
        Object obj1 = itr.next();
        Integer io1 = (Integer) obj1;
        int x1 = io1.intValue();
        s1 = s1 + x1;
    }
    System.out.println("SUM USING iterator () = " + s1);
    ListIterator<Integer> litr = ll.listIterator();
    while (litr.hasNext()) {
        Object obj2 = litr.next();
        System.out.print(obj2 + ",");
    }
    System.out.println("\n");
    while (litr.hasNext()) {
        Object obj3 = litr.next();
        System.out.print(obj3 + ",");
    }
    System.out.println("\n");
    Object obj4 = ll.get(2);// random retrieval
    System.out.println(obj4);

Answer 2

The first answer (by Nandkumar) is right, I'd also check the runtime error, caused by this lines:

while (litr.hasPrevious ())  
    {  
        Object obj3=litr.next ();  
        System.out.print (obj3+",");  
    }

That is: you check if your iterator has a "previous" item, then go for tne "next"? Probably not what you intended to do.

The "error" at compile time is only a warning, you can run your program after compilation, but the compiler is telling you that it found something strange in your code.

Answer 3

I executed your program through eclipse :

Just use LinkedList<Integer> instead of just LinkedList. No Warnings.

Output =>

CONTENTS OF l1 = []
SIZE = 0
CONTENTS OF ll = [10, 20, 30, 40]
SIZE = 4
SUM USING toArray () = 100
CONTENTS OF ll = [6, 5, 10, 20, 30, 40]
SIZE = 6
SUM USING iterator () = 111
6,5,10,20,30,40,

Exception in thread "main" java.util.NoSuchElementException
    at java.util.LinkedList$ListItr.next(Unknown Source)
    at com.Linkedlist.main(Test.java:46)