Java BubbleSort Array List w/ multiple fields

Question

I have a List of row objects. Each row has an id, name, and population.

Example:

Row x = new Row(305, Miami, 2.2);

I want to list the rows alphabetically by name using bubble sort. I know I need 2 loops for the bubble sort. This is what I get

protected void nameBubbleSort(List<AbstractRow> a) {
        a=getcList();
    int size = a.size();
    int end = size-1; // size-1, so you don't get an IndexOutOfBoundsException
    boolean sorted = false;
    for(int i = 0; i < size-1 && !sorted; i++) 
    {
        sorted = true; // if you never execute a swap, the list is already sorted
        for (int j=0; j<end; j++) {
            AbstractRow t1 = (AbstractRow) a.get(j);
            AbstractRow t2 = (AbstractRow) a.get(j+1); // j+1, so you don't change the value of i
            if(t1.getName().compareTo(t2.getName()) > 0)
            { 
                sorted = false;
                a.remove(j);
                a.add(j+1, t1); // j+1, so you don't change the value of i
            }
        }
        end--;
    }

    for(int i = 0; i<size; i++)
    {
        AbstractRow tmp = (AbstractRow) getcList().get(i);
        System.out.println(tmp.toString()); }
    }
    protected void bubbleSortName(List<AbstractRow> list) {
        list = getcList();
        int n = list.size();
        int temp = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 1; j < (n - i); j++) {
                if (list.get(j - 1).getName() compareTo list.get(j).getName()) {
                    //swap elements  
                    temp = aList.get(j - 1);
                    aList.set(j-1, aList.get(j));
                    aList.set(j, temp);
                }
            }
        }
    }

I then want to go back and sort using the id number.

Help please

protected void nameBubbleSort(List<AbstractRow> a) {
        a=getcList();
    int size = a.size();
    int end = size-1; // size-1, so you don't get an IndexOutOfBoundsException
    boolean sorted = false;
    for(int i = 0; i < size-1 && !sorted; i++) 
    {
        sorted = true; // if you never execute a swap, the list is already sorted
        for (int j=0; j<end; j++) {
            AbstractRow t1 = (AbstractRow) a.get(j);
            AbstractRow t2 = (AbstractRow) a.get(j+1); // j+1, so you don't change the value of i
            if(t1.getName().compareTo(t2.getName()) > 0)
            { 
                sorted = false;
                a.remove(j);
                a.add(j+1, t1); // j+1, so you don't change the value of i
            }
        }
        end--;
    }

    for(int i = 0; i<size; i++)
    {
        AbstractRow tmp = (AbstractRow) getcList().get(i);
        System.out.println(tmp.toString()); }
    }
    protected void bubbleSortName(List<AbstractRow> list) {
        list = getcList();
        int n = list.size();
        int temp = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 1; j < (n - i); j++) {
                if (list.get(j - 1).getName() compareTo list.get(j).getName()) {
                    //swap elements  
                    temp = list.get(j - 1);
                    list.set(j-1, list.get(j));
                    list.set(j, temp);
                }
            }
        }
    }

I know how to loop through the array list and get the length of each name, I'm just having a hard time pointing to the right object in the arrayList. I know thats what I have getName() and getID set up.

Alexander Ivanchenko · Accepted Answer · 2022-11-29 09:10:18Z

You don't need to operate via remove() and add(). Instead, you can use List.set() to swap the elements.

protected void nameBubbleSort(List<AbstractRow> a) {
    
    for (int i = 0; i < a.size(); i++) {
        for (int j = 0; j < a.size() - 1 - i; j++) {
            AbstractRow t1 = a.get(j);
            AbstractRow t2 = a.get(j + 1);
            if (t1.getName().compareTo(t2.getName()) > 0) { // swap the elements
                a.set(j, t2);
                a.set(j + 1, t1);
            }
        }
    }
}

You might also want to lean about Comparator, in a nutshell it is a special object which facilitates comparison of elements. You can use it a similar way you've used method compareTo() (in real life scenarios while it is used with built-in sorting, or methods like Collections.max(), Stream.max(), etc.)

public static final Comparator<AbstractRow> BY_NAME = Comparator.comparing(AbstractRow::getName);

protected void nameBubbleSort(List<AbstractRow> a) {
    
    for (int i = 0; i < a.size(); i++) {
        for (int j = 0; j < a.size() - 1 - i; j++) {
            AbstractRow t1 = a.get(j);
            AbstractRow t2 = a.get(j + 1);
            if (BY_NAME.compare(t1, t2) > 0) { // swap the elements
                a.set(j, t2);
                a.set(j + 1, t1);
            }
        }
    }
}

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