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Thread: Arraylist removing element

  1. #1
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    Default Arraylist removing element

    Hi

    i have an arraylist thats keeping a track of members, i need to remove a member and have the list push all other elements down by 1. Please help

     
    ArrayList<Membership> member;
     ArrayList<Books> book;
     private int nextMemberID;
     private int nextBookId;
        /**
         * Constructor for objects of class Library
         */
        public Library() 
        {
     
           nextMemberID = 1;
           nextBookId = 1;
     
           member = new ArrayList<Membership>();
           book = new ArrayList<Books>();
     
     
        }
     
     
     
     
     
    public void removeMember(int ID) {
        //First we find the lot with the given number
        Membership membership = getMember(ID);
        if (membership != null) {
            //Then we can use the method remove with lot as argument
           member.remove(membership);
           nextMemberID--;
     
        }
     
    }


  2. #2
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    Default Re: Arraylist removing element

    sorry i didn't mean the element because they do move down as you remove objects, i meant to get my "nextMemberID" to shuffle down by 1 so as to fill the gap.

  3. #3
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    Default Re: Arraylist removing element

    I'm not sure what the question really is...it seems your code removes an element, and decrements a marker. I'd suggest an SSCCE to more clearly demonstrate the behavior you get vs the behavior you want.

  4. #4
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    Default Re: Arraylist removing element

    Ok i can see my question isn't clear so i'll try to explaine. if i add 10 members to the array then the array will hold these members in cells 0-9. My "nextMemberID" will hold these members as 1-10.

    If i remove a member (say member 3) then the array will hold them as 0-8 but my "nextMemberID" will have a gap in the number line where 3 was

    e.g 1-2 4-10.

    Now my nextMemberID-- means that the next member i input will go into array cell 9 but nextMeberID cell 10 which is already in use.

    Hope this helps.

  5. #5
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    Default Re: Arraylist removing element

    Still confused so you'll have to clarify with either a better code example or description. I have no idea what your nextMemberID is used for (its an int, so how can it have a gap?), but based upon its name and description presume all you want it to do is represent member.size() + 1 ?

  6. #6
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    Default Re: Arraylist removing element

    Here is how i add a member, When i add a member it adds one to the nextMemberID int. So if i add member 4 to the list of 3 members then i'll have 4 members 1,2,3,4. If i remove member 2 then i'll have 1,3,4 but i dont want it to hold the numbers like this, i need the numbers to move down so when i print them it will have their numbers as 1,2,3.

    if i have 4 members then the next MemberID number will be 5, but if i remove a member then it will drop the next MemeberID number to 4 but i will still have members 1,3,4. So the next time i add a member it will want to add a MemberID of 4 so i end up with 1,3,4,4.

       public void addnewMember( String first, String last, String telephone)
        {
     
        member.add(new Membership(nextMemberID,first,last,telephone));
        nextMemberID++; 
    }


     
    public class Membership
    {
     
        private String firstName;
        private String lastName;
        private String telephoneNumber;
        private int ID;
     
     
        /**
         * Constructor for objects of class Member
         */
        public Membership(int ID, String first, String last, String telephone)
        {
           this.ID = ID;
           this.firstName = first;
           this.lastName = last;
           this.telephoneNumber = telephone;
     
     
        }
     
        /**
         * @return The member's number.
         */
        public int getID()
        {
            return ID;
        }

  7. #7
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    Default Re: Arraylist removing element

    all depends on what u want. Do u want the ID to represent the position in list of members? Do u want same ID not to be used twice or more (after removing ID 2 not to have it used again)? Or u want removed ID to be used again?

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