Working on my coursework here thats asks to create code to search a linked list of linearnodes holding comparable items. I've created the list but can't seem to get it so that when I enter a target value it comes up that it's not found in the list.. when its actually in the list. Hoping someone can have a look and help me out thanks.

import java.util.Scanner;
import java.io.*;
public class Wk6
{
public static int size =4;

public static void main(String[] args)throws IOException
{
Account1 user;
String name;
long account;
double initial;
Object target;
long answer;
int result;

LinearNode list = null;
LinearNode temp;

Scanner sc = new Scanner(new File("hello.txt"));
Scanner kbScan = new Scanner(System.in);


for(int i =0; i<size; i++)
{

name = sc.next();
account = sc.nextLong();
initial = sc.nextDouble();

user = new Account1(name, account, initial);
temp = new LinearNode(user);
temp.setNext(list);
list = temp;
}

printList(list);
countList(list);

System.out.println("Enter an account number you would like to search for:");
answer = kbScan.nextLong();
target=answer;

result=search(list, target);

if(result!=-1){
System.out.println("Found in position:\n" + result);
}
else {
System.out.println("Not found");
}

}

public static void printList(LinearNode L)
{
LinearNode temp = L;

while (temp != null)
{
System.out.println(temp.getElement());
temp = temp.getNext();
}

}

// iterative Method
public static void countList(LinearNode L)
{

LinearNode temp = L;
int counter = 0;

while(temp != null)
{
counter++;
temp = temp.getNext();
}

System.out.println("Number of Counters:" + counter);
}


public static int search(LinearNode L, Object target)
{
LinearNode temp = L;

int index =0;
int found = -1;
while(found==-1 && index<size)
{


if ((temp.getElement()).equals(target))

found = index;
index++;
L=(L.getNext()).getNext();


}
return found;
}

...to create code to search a linked list of linearnodes holding comparable items..
You should use a LinkedList Implementation with Comparable Interface Objects.

You are thinking on C (Pointers) Linked List.

temp.setNext(list);
list = temp; 	

while (temp != null)
{
  System.out.println(temp.getElement());
  temp = temp.getNext();
}

public static void countList(LinearNode L) {
  LinearNode temp = L;
  int counter = 0;
  while(temp != null)
  {
    counter++;
    temp = temp.getNext();
  }
  System.out.println("Number of Counters:" + counter);
}

In Java LinkedList is implemented with Collections (The List Interface)

LinkedList.add(item);
List.add(item);

for (Account1 account : allAccounts) {
  System.out.println(account.name);
}

public static void countList(LinkedList L) {
  System.out.println("Number of Accounts:" + L.size().toString());
}

Further information (Trail: Collections):
http://java.sun.com/docs/books/tutorial/collections/index.html


Good luck!
Hackman

: Working on my coursework here thats asks to create code to search a
: linked list of linearnodes holding comparable items. I've created
: the list but can't seem to get it so that when I enter a target
: value it comes up that it's not found in the list.. when its
: actually in the list. Hoping someone can have a look and help me out
: thanks.
:
: import java.util.Scanner;
: import java.io.*;
: public class Wk6
: {
: public static int size =4;
:
: public static void main(String[] args)throws IOException
: {
: Account1 user;
: String name;
: long account;
: double initial;
: Object target;
: long answer;
: int result;
:
: LinearNode list = null;
: LinearNode temp;
:
: Scanner sc = new Scanner(new File("hello.txt"));
: Scanner kbScan = new Scanner(System.in);
:
:
: for(int i =0; i<size; i++)
: {
:
: name = sc.next();
: account = sc.nextLong();
: initial = sc.nextDouble();
:
: user = new Account1(name, account, initial);
: temp = new LinearNode(user);
: temp.setNext(list);
: list = temp;
: }
:
: printList(list);
: countList(list);
:
: System.out.println("Enter an account number you would like
: to search for:");
: answer = kbScan.nextLong();
: target=answer;
:
: result=search(list, target);
:
: if(result!=-1){
: System.out.println("Found in position:\n" + result);
: }
: else {
: System.out.println("Not found");
: }
:
: }
:
: public static void printList(LinearNode L)
: {
: LinearNode temp = L;
:
: while (temp != null)
: {
: System.out.println(temp.getElement());
: temp = temp.getNext();
: }
:
: }
:
: // iterative Method
: public static void countList(LinearNode L)
: {
:
: LinearNode temp = L;
: int counter = 0;
:
: while(temp != null)
: {
: counter++;
: temp = temp.getNext();
: }
:
: System.out.println("Number of Counters:" + counter);
: }
:
:
: public static int search(LinearNode L, Object target)
: {
: LinearNode temp = L;
:
: int index =0;
: int found = -1;
: while(found==-1 && index<size)
: {
:
:
: if ((temp.getElement()).equals(target))
:
: found = index;
: index++;
: L=(L.getNext()).getNext();
:
:
: }
: return found;
: }
:
In your search() method you skip every other node, and you compare the target with only the first node. I've marked the wrong lines in red above.

: : Working on my coursework here thats asks to create code to search a
: : linked list of linearnodes holding comparable items. I've created
: : the list but can't seem to get it so that when I enter a target
: : value it comes up that it's not found in the list.. when its
: : actually in the list. Hoping someone can have a look and help me out
: : thanks.
: :
: : import java.util.Scanner;
: : import java.io.*;
: : public class Wk6
: : {
: : public static int size =4;
: :
: : public static void main(String[] args)throws IOException
: : {
: : Account1 user;
: : String name;
: : long account;
: : double initial;
: : Object target;
: : long answer;
: : int result;
: :
: : LinearNode list = null;
: : LinearNode temp;
: :
: : Scanner sc = new Scanner(new File("hello.txt"));
: : Scanner kbScan = new Scanner(System.in);
: :
: :
: : for(int i =0; i<size; i++)
: : {
: :
: : name = sc.next();
: : account = sc.nextLong();
: : initial = sc.nextDouble();
: :
: : user = new Account1(name, account, initial);
: : temp = new LinearNode(user);
: : temp.setNext(list);
: : list = temp;
: : }
: :
: : printList(list);
: : countList(list);
: :
: : System.out.println("Enter an account number you would like
: : to search for:");
: : answer = kbScan.nextLong();
: : target=answer;
: :
: : result=search(list, target);
: :
: : if(result!=-1){
: : System.out.println("Found in position:\n" + result);
: : }
: : else {
: : System.out.println("Not found");
: : }
: :
: : }
: :
: : public static void printList(LinearNode L)
: : {
: : LinearNode temp = L;
: :
: : while (temp != null)
: : {
: : System.out.println(temp.getElement());
: : temp = temp.getNext();
: : }
: :
: : }
: :
: : // iterative Method
: : public static void countList(LinearNode L)
: : {
: :
: : LinearNode temp = L;
: : int counter = 0;
: :
: : while(temp != null)
: : {
: : counter++;
: : temp = temp.getNext();
: : }
: :
: : System.out.println("Number of Counters:" + counter);
: : }
: :
: :
: : public static int search(LinearNode L, Object target)
: : {
: : LinearNode temp = L;
: :
: : int index =0;
: : int found = -1;
: : while(found==-1 && index<size)
: : {
: :
: :
: : if ((temp.getElement()).equals(target))
: :
: : found = index;
: : index++;
: : L=(L.getNext()).getNext();
: :
: :
: : }
: : return found;
: : }
: :
: In your search() method you skip every other node, and you compare
: the target with only the first node. I've marked the wrong lines in
: red above.


Thanks I knew it was something to do with the search method because everything else seems to work ok. Just can't get that bit right, any ideas on how I can get it to search every other one instead of just the first one?? Thanks x

: : : public static int search(LinearNode L, Object target)
: : : {
: : : LinearNode temp = L;
: : :
: : : int index =0;
: : : int found = -1;
: : : while(found==-1 && index<size)
: : : {
: : :
: : :
: : : if ((temp.getElement()).equals(target))
: : :
: : : found = index;
: : : index++;
: : : L=(L.getNext()).getNext();
: : :
: : :
: : : }
: : : return found;
: : : }
: : :
: : In your search() method you skip every other node, and you compare
: : the target with only the first node. I've marked the wrong lines in
: : red above.
:
:
: Thanks I knew it was something to do with the search method because
: everything else seems to work ok. Just can't get that bit right, any
: ideas on how I can get it to search every other one instead of just
: the first one?? Thanks x
:
:
First you need to check which variable holds which value:

- L is the first node
- temp is the currect node

In your code you are checking if temp equals the target. Then you move the L variable to the next's next node. Here's a simple example of how your code performs its search:

1  LinearNode temp = L;
2  while(found==-1 && index<size) {	
3	if ((temp.getElement()).equals(target))
4		found = index;
5	L=(L.getNext()).getNext();
6  }

given this list: 1, 2, 3, 4, 5 and target = 2.
Before line 1: L = 1
Then after line 1: temp = 1
In line 3 you compare temp to the target (i.e. 1.equals(2)) which is false.
In line 5 you call L.getNext() (L = 2, inside brackets) and immediately call it again (L = 3, outside the brackets).
Then back to line 2, and the loop continues.
Again line 3 is executed: temp is compared to the target (i.e. 1.equals(2)) which is false.
And then line 5 is executed again: L = 4 and L = 5.
For the last time back to line 3.
Still comparing temp to the target.
Now inside the brackets in line 5 the next node is retrieved (L = null). And then getNext() is called again, but this time the object is null, throwing a NullPointerException.
As you can see there are 2 mistakes in your code: line 3 and line 5. In line 3 you're checking the value of temp, but that variable always remains at the first node. In line 5 you're updating the variable L twice per iteration through the loop. This should only happen once.

: : : : public static int search(LinearNode L, Object target)
: : : : {
: : : : LinearNode temp = L;
: : : :
: : : : int index =0;
: : : : int found = -1;
: : : : while(found==-1 && index<size)
: : : : {
: : : :
: : : :
: : : : if ((temp.getElement()).equals(target))
: : : :
: : : : found = index;
: : : : index++;
: : : : L=(L.getNext()).getNext();
: : : :
: : : :
: : : : }
: : : : return found;
: : : : }
: : : :
: : : In your search() method you skip every other node, and you compare
: : : the target with only the first node. I've marked the wrong lines in
: : : red above.
: :
: :
: : Thanks I knew it was something to do with the search method because
: : everything else seems to work ok. Just can't get that bit right, any
: : ideas on how I can get it to search every other one instead of just
: : the first one?? Thanks x
: :
: :
: First you need to check which variable holds which value:
:
: - L is the first node
: - temp is the currect node
:
: In your code you are checking if temp equals the target. Then you
: move the L variable to the next's next node. Here's a simple example
: of how your code performs its search:
:

: 
: 1  LinearNode temp = L;
: 2  while(found==-1 && index<size) {	
: 3	if ((temp.getElement()).equals(target))
: 4		found = index;
: 5	L=(L.getNext()).getNext();
: 6  }
: 

:
: given this list: 1, 2, 3, 4, 5 and target = 2.
: Before line 1: L = 1
: Then after line 1: temp = 1
: In line 3 you compare temp to the target (i.e. 1.equals(2)) which is
: false.
: In line 5 you call L.getNext() (L = 2, inside brackets) and
: immediately call it again (L = 3, outside the brackets).
: Then back to line 2, and the loop continues.
: Again line 3 is executed: temp is compared to the target (i.e.
: 1.equals(2)) which is false.
: And then line 5 is executed again: L = 4 and L = 5.
: For the last time back to line 3.
: Still comparing temp to the target.
: Now inside the brackets in line 5 the next node is retrieved (L =
: null). And then getNext() is called again, but this time the object
: is null, throwing a NullPointerException.
: As you can see there are 2 mistakes in your code: line 3 and line 5.
: In line 3 you're checking the value of temp, but that variable
: always remains at the first node. In line 5 you're updating the
: variable L twice per iteration through the loop. This should only
: happen once.

Thanks, I understand what you mean. Going to have a go at it now, thanks x