[silvia]

Please i need help.

Code:

class Node
{

public Object data;
public Node next;

public Node()
{
this.data = null;
this.next = null;
}

public Node(Object a)
{
this.data = a;
this.next = null;
}

public Node(Object a, Node b)
{
this.data = a;
this.next = b;
}

}

Code:

public class List
{
private Node head;
private Node tail;
public List()
{
this.head = null;
this.tail = null;
}
public void insertAtFront(Object obj)
{
if (this.size()==0)
{
Node n = new Node(obj);
this.head = n;
this.tail = n;
}
else
{
Node n = new Node(obj);
n.next = this.head;
this.head = n;
}
}
public void insertAtBack(Object obj)
{
if (this.size()==0)
{
Node n = new Node(obj);
this.head = n;
this.tail = n;
}
else
{
Node n = new Node(obj);
this.tail.next = n;
this.tail = n;
}
}
public Object removeFromFront()
{
if (this.size()==0)
{
System.out.println("No data to remove.");
return null;
}
else if (this.size()==1)
{
Object a = this.head.data;
this.head = null;
this.tail = null;
return a;
}
else
{
Object a = this.head.data;
this.head = this.head.next;
return a;
}
}

Code:

public void insertAtSorted(String s)
{
if (this.size()==0)
{
insertAtFront(s);
return;
}
else if (s<=this.head)// stuck on these type of statements
{
insertAtFront(s);
return;
}
else if (s>=this.tail) // how to make so this works? <----------
{
insertAtBack(s);
return;
}
else
{
Node ntlnode = this.head;
while (ntlnode.next <= s)
{
ntlnode = ntlnode.next;
Node blah = new Node(s);
blah.next = ntlnode;
this.next = blah;
}
}
}

Code:

public Object removeFromBack()
{
if (this.size()==0)
{
System.out.println("No data to remove.");
return null;
}
else if (this.size()==1)
{
Object a = this.tail.data;
this.head = null;
this.tail = null;
return a;
}
else
{
Object a = this.tail.data;
Node ntlnode = this.head;
while (ntlnode.next != this.tail)
{
ntlnode = ntlnode.next;
}
this.tail = ntlnode;
this.tail.next = null;
return a;
}
}
public boolean isEmpty()
{
return this.head == null;
}
public void print()
{
if (this.size()==0)
{
System.out.println("Empty list!");
return;
}
Node curr = this.head;
while (curr != null)
{
System.out.println(curr.data.toString());
curr = curr.next; //move forward to the next data item.
}
System.out.println();
}
public int size()
{
int count = 0;
Node curr = this.head;
while (curr != null)
{
count++;
curr = curr.next;
}
return count;
}
}

The error is:

Code:

List.java:100: operator <= cannot be applied to java.lang.String,java.lang.Object
else if (s<=this.head.data) //not sure about this format of object<---------------
^
List.java:105: operator >= cannot be applied to java.lang.String,java.lang.Object
else if (s>=this.tail.data)
^
List.java:113: operator <= cannot be applied to Node,java.lang.String
while (ntlnode.next <= s)
^
List.java:118: cannot find symbol
symbol : variable next
location: class List
this.next = blah;
^
4 errors

Thanks