adding and deleting from ordered Arraylist

Question

I need to add an Object to an ordered ArrayList depending on an attribute inside of the Object. I know how to use the .add method to add the object but I don't know how to search for the right place for it using the compareTo() method. And also I need to remove an Object from the ArrayList if the Object contains a certain String but I cant figure out how to access the Object attributes from the ArrayList.

Realtor Object

/**
 * Constructor for Realtor object using parameter
 * @param readData - array of data from line
 */ 
public Realtor(String[]readData){
    licenseNumber = readData[2];
    firstName = readData[3];
    lastName = readData[4];
    phoneNumber = readData[5];
    commission = Double.parseDouble(readData[6]);
}

RealtorLogImpl

public class RealtorLogImpl {

    private ArrayList<Realtor> realtorList;

     /**
     * Add Realtor object to ordered list
     * @param obj - Realtor object
     */
    public void add(Realtor obj){

       //needs to be added into correct place depending on Realtor licenseNumber
        realtorList.add(obj);
    }

    /**
     * Delete Realtor object from list if license matches
     * and return true if successful
     * @param license
     * @return 
     */
    public boolean remove (String license){
      //need to remove Realtor with specific licenseNumber and return true if successful
    }

List<String> list = new ArrayList<>(); and if (list.get(13).length() == 42) {...} — Joop Eggen
– Joop Eggen, Commented May 21, 2017 at 21:11
What is the type of the objects in the list? If the type is literally just Object, what does it mean for an element to "contain" a string? — Daniel Pryden
– Daniel Pryden, Commented May 21, 2017 at 21:12
First, does the Object implement an .equals() that has the "certain String"? If so, then the .remove(object) will work. Otherwise, you'll need to use an Iterator, which will allow you to get the Object, and then use the standard methods to retrieve the value and compare. Second, do you really need an ArrayList (See: Why Is there No Sorted List). Best approach is just to add and then sort with an appropriate comparator. — KevinO
– KevinO, Commented May 21, 2017 at 21:12
thank @KevinO I needed to be able to access the values in the Object — Tommy Barrett
– Tommy Barrett, Commented May 21, 2017 at 21:19

Eli Miller · Accepted Answer · 2017-05-21 21:19:25Z

1

I'm assuming you are using java 8. Some of these things have not been implemented in java 7 so keep that in mind.

First, to remove the items I would recommend using the removeif() method on the arraylist. This takes a lambda expression which could be something like x -> x.getString().equals("someString").

Second, You could add the object to the array then simply sort the array afterwards. You would just have to write a comparator to sort it by.

answered May 21, 2017 at 21:19

Eli Miller

865 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user3429660 · Accepted Answer · 2017-05-21 21:30:35Z

Here is some basic code; I have no compiler here, so you might find small errors/typos.

I'm sure there are better classes you can use instead of managing your own ordered list.

To insert:

public bool add(Realtor obj) {
    int idx = 0;
    for (Realtor s : realtorList) {
        if (s.licenseNumber.equals(item.licenseNumber)) {
           return false; // Already there
        }
        if (s.licenseNumber.compareTo(item.licenseNumber) > 0) {
           orderedList.add(idx, item);
           return true; // Inserted
        }
        idx++;
    }
    orderedList.add(item);
    return true; // Appended
}

To delete:

public bool deleteItem(String license) {
    int idx = 0;
    for (Realtor s : realtorList) {
        if (s.licenseNumber.equals(license)) {
           realtorList.remove(idx);
           return true; // Removed
        }
    }
    return false; // Not found
}

Marteng · Accepted Answer · 2017-05-21 21:40:08Z

To answer your question check the following snippet (requires Java 8) and adapt on your demand:

public static void main(String[] args) {

    final List<String> list = new ArrayList<>();
    list.add("Element 1");
    list.add("Element 2");
    list.add("Element 3");

    /*
     * Insert at a specific position (add "Element 2.5" between "Element 2" and "Element 3")
     */
    Optional<String> elementToInsertAfter = list.stream().filter(element -> element.equals("Element 2")).findFirst();
    if(elementToInsertAfter.isPresent()) {
        list.set(list.indexOf(elementToInsertAfter.get()) + 1, "Element 2.5");
    }

    /*
     * Remove a particular element (in this case where name equals "Element 2")
     */
    list.removeIf(element -> element.equals("Element 2"));
}

#add(element) just adds an element to the list. In case of an ArrayList it's added at the end. If you want to insert an element at a particular position you need to use #set(index,element)

But instead of inserting your element at a particular position manually you should maybe use a comparator instead. See java.util.List.sort(Comparator<? super E> e)

Collectives™ on Stack Overflow

adding and deleting from ordered Arraylist

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related