A question in searching a link in a circular list

[transgalactic]

i was told to build a method for which if
we find the asked value in one of the links we
return the previous link
i have built a method that supposedly does it
the problem is that i was told that this code is wrong because
we need to check the "this" link seperatly from the FOR loop
why is that?

public static  Link find(Object x)
Link p;//current object
Link t;//previous object
for (p=Link;(p!=this);p=p.next, t=p)
{
if (p.data.equals(x)){
 return t;
 
}
return null;
}

 

[D H]

That isn't valid c++ code.
- 'this' is doesn't exist in a static member function.
- There is no left operand for the && operator in the for loop.

 

[transgalactic]

its JAVA not C++

 

[D H]

The same comments apples to Java. From http://www.owlnet.rice.edu/~tchjava/2002/notes/current/node53.html ,

Similarly, the code in a static method cannot refer to this or to the fields of this because there is no class instance to serve as the receiver for such an access.

"&&" is a binary infix conditional operator in Java. Binary: "&&" needs two operands on which to operate. Infix: the two operands go to the left and right of the operator. Conditional: If the left operand is false so is the expression.

 

[transgalactic]

i removed &&i changed the post

the link doesn't talk about linked listcan you answer my original post??

 

[D H]

The link talks about using the parameter this in a static method. You cannot do that. Why did you use the word "static" doing at the start of the code? You cannot use this in a static method. You have other errors as well, such as "p=Link". "Link" is a class; I suspect you meant "p=this" instead. Of course, if you do start with "p=this", the code will never enter the loop as written.

 

[jambaugh]

One problem that I see is:

If your first link happens to be the one where you find the value then the t-pointer to the previous link will not yet be assigned.

 

[transgalactic]

ok i ment p=this
and suppose that its not static
so what know
i don't understand this comment
"if you do start with "p=this", the code will never enter the loop as written"
its starts with this then in the for loop i say that p=p.next
so it goes further
and checks "p" again which represents the next link
i was told to start the for loop from p=this.next
and to check "this" object seperatly
i don't know why?

 

[D H]

It is a good idea to trace through code by hand. Doing that with this chunk of code,

for (p=this; p != this; p= p.next) {
  < loop body >
}

The variable p is initially set to this. The termination condition is then checked. p is equal to this, so the body of the loop is never entered. Starting with p.next initially prevents this problem, but creates a new one. The body of the loop is never performed with this itself. That is easily rectified in this case as the body of this particular loop is a one-liner.

 

[transgalactic]

ahhhhhhhhhh ok thanks