cannot find symbol for "list.addFirst"

[alexbryan_08]

Can somebody help me with this code..

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

public class ListPerformanceDemo
{
final int SIZE = 100000;

public ListPerformanceDemo()
{
System.out.println(Integer.MAX_VALUE + "\n\n");

ArrayList<String> arrayL = new ArrayList<String>();
System.out.println("time for ArrayList = " + timeAddFrontofList(arrayL));

LinkedList<String> linkedL = new LinkedList<String>();
System.out.println("time for LinkedList = " + timeAddFrontofList(linkedL));
}

//Add object to the front of the list using addFirst


long timeAddFrontofList(List list)
{
long start = System.currentTimeMillis();

for (int i = 0; i < SIZE; i++)
{
String s = new String(i + " ");
// add object to the front of the list
list.addFirst(s);
}

return System.currentTimeMillis() - start;
}

public static void main(String args[])
{
new ListPerformanceDemo();
}
}//end class


apparently this code will work if i change it to list.add(0,s), but i want to use list.addFirst(s)..
what should i change??
:confused::confused:

[alexbryan_08]

owh..
and i actually want to add new object on the at the front of the list..

[Fubarable]

What is this addFirst method? Where in the API have you seen this? You know that you can't just make up a method for an existing class and expect mathemagically that it will work.

[r035198x]

addFirst is a method in LinkedList. You are trying to call it on an ArrayList which is not a LinkedList. Better have the API specs open as you are coding.

[alexbryan_08]

What is this addFirst method? Where in the API have you seen this? You know that you can't just make up a method for an existing class and expect mathemagically that it will work.

DataStructures
Class LinkedList

java.lang.Object
|
+--DataStructures.LinkedList
public class LinkedList
extends java.lang.Object
A simple implementation of singly linked lists.

Lists are created empty, for example:

LinkedList list = new LinkedList();

after which items can be inserted at the front of the list by
list.addFirst(item)

-retrieve from website www[dot]informatics[dot]susx[dot]ac[dot]uk/courses/dats/DataStructures/docs/DataStructures/LinkedList

[Fubarable]

Wrong info -- deleted

[Fubarable]

addFirst is a method in LinkedList. You are trying to call it on an ArrayList which is not a LinkedList. Better have the API specs open as you are coding.

Arg, so it is. He's calling it on the List interface actually, and that is the API that I looked up. My bad. Please ignore what I stated above!

[alexbryan_08]

addFirst is a method in LinkedList. You are trying to call it on an ArrayList which is not a LinkedList. Better have the API specs open as you are coding.

im sorry..
i dont understand..
im pretty new on this..
just learned it this sem..
wat u mean wit specs open?
:confused::confused:

[mrmatt1111]

You have this method:

long timeAddFrontofList(List list)
{
...
}

It is saying you have a variable named 'list' of class 'List'. The class List does not have a method 'addFirst' only the class LinkedList does.

Specs:

List
LinkedList
ArrayList

[alexbryan_08]

owh..
no wonder..
change List -> LinkedList..

problem solved..
thanks everyone..
:):)

[r035198x]

owh..
no wonder..
change List -> LinkedList..

problem solved..
thanks everyone..
:):)

By specs I meant API specs. Here is a sample. Programming without those is like shooting in the dark. You could even shoot your own foot.