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Thread: Deleting an element out of a linked list with boolean method

  1. #1
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    Default Deleting an element out of a linked list with boolean method

    Hey, long time no see?

    Jokes aside, I need to implement a delete method now. It is boolean as well but it uses a diffrent parameter. I've tested the code, teh insert method works fine, but the delete doenst.After I try to delete a Person the size stays the same.

     
    public boolean delete(String name) {
    		Node p = head;
     
    		if( p == null) {
    			size--;
    			return true;
    		}else {
     
    			Node temp = p;
    			int comparison;
    			while(temp.next != null) {
    				comparison = temp.person.name.compareTo(name);
    				if(comparison == 0) {
    					temp.next = temp.next.next;
    					size--;
    					return true;
    				} else {
    					temp = temp.next;
     
    				}
    			}
    		}return false;
    	}

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Deleting an element out of a linked list with boolean method

    Time for some debugging. Add some print statements that print out the values of variables as they are used and to show the execution path.
    The print out will show you what the computer sees when the code is executed and help you find the problem.


    One problem I see is the size of an empty list is decreased by 1.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Deleting an element out of a linked list with boolean method

    Aight I did some tweaks and now I've got this;

     
    public boolean delete(String name) {
            if (head == null)
                return false;
            if (head.name.compareTo(name) == 0) {
                head = head.next;
                size--;
                return true;
            }
     
            Node current = head;
            Node prev = head;
            while (current != null) {
                if (current.name.compareTo(name) == 0) {
                    prev.next = current.next;
                    size--;
                    return true;
                }
                prev = current;
                current = current.next;
            }
        }
    And this error comes up, I think I've had it before

    PhoneBookList.java:48: error: cannot find symbol
    if (head.name.compareTo(name) == 0) {
    ^
    symbol: variable name
    location: variable head of type Node
    PhoneBookList.java:57: error: cannot find symbol
    if (current.name.compareTo(name) == 0) {
    ^
    symbol: variable name
    location: variable current of type Node
    2 errors

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Deleting an element out of a linked list with boolean method

    PhoneBookList.java:48: error: cannot find symbol
    if (head.name.compareTo(name) == 0) {
    ^
    symbol: variable name
    location: variable head of type Node
    The compiler can not find a member named name in the Node class (head)

    Yes, that look familiar. Remember name is in the Person class that is inside of the Node class.
    refToNode.refToPerson.name
    If you don't understand my answer, don't ignore it, ask a question.

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    Wink Re: Deleting an element out of a linked list with boolean method

    Yep,I've had that fixed it works:

     
    public boolean delete(String name) {
            if (head == null)
                return false;
            if (head.person.name.compareTo(name) == 0) {
                head = head.next;
                size--;
                return true;
            }
     
            Node current = head;
            Node prev = head;
            while (current != null) {
                if (current.person.name.compareTo(name) == 0) {
                    prev.next = current.next;
                    size--;
                    return true;
                }
                prev = current;
                current = current.next;
            }
    		return false;
        }

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: Deleting an element out of a linked list with boolean method

    Is it working now?
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Deleting an element out of a linked list with boolean method

    Yea works just fine

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