Doing a Selection sort on an ArrayList

Question

I need to sort the array list from highest to lowest based on the "value" and im really stuck :( basically in this project, they are gonna run a list of items and this method is supposed to put the one with the highest value first and so fort and im trying to use a selection sort. Thank for you help in advance :) here is what i have at the moment

public void pickMostExpensiveFirst(ArrayList<Item> totalListOfItems)
{
    int max, i ,j;
    Item temp;

    for (i = 0; i < totalListOfItems.size() - 1; i++)
    {
        max = i;

        for (j = i + 1; j < totalListOfItems.size(); j++)
        {
            if (totalListOfItems.get(max).getValue()
                    .compareTo(totalListOfItems.get(j).getValue()) > 0)
                max = j;
        }

        temp = totalListOfItems.get(i);
        totalListOfItems.set(i, totalListOfItems.get(max));
        totalListOfItems.set(max, temp);
    }
}

LeleDumbo · Accepted Answer · 2013-10-27 11:38:06Z

1

Your problem lies here:

if (totalListOfItems.get(max).getValue().compareTo(totalListOfItems.get(j).getValue()) > 0)
  max = j;

here you compare item at position max and j, and if item(max) > item(j), you replace max with j. This is basically searching for LOWEST value, not HIGHEST. Switch it over, and your problem is solved.

answered Oct 27, 2013 at 11:38

LeleDumbo

9,3804 gold badges26 silver badges38 bronze badges

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

Comments

Kedar Tokekar · Accepted Answer · 2017-08-15 04:03:52Z

0

Java helps Object Oriented programming, why to implement from scratch when Java collection framework (along with supporting classes) provides ready made proved solutions.

If the objective of your method is just to identify the maximum/ minimum or sort list, then java.util.Collections class provides util methods. only requirement is that your Item class should be (IsA relationship) Comparable, meaning Item should implement Comparable interface. If you do not have control over Item class code, then we can use Interface Comparator to provide comparison rule. the sample code looks as follows.

public static void pickMostExpensiveFirst(ArrayList<Item> totalListOfItems) {
    System.out.println(Collections.max(totalListOfItems));
    // Collections.sort(totalListOfItems); // to sort with Comparable
    // Collections.sort(totalListOfItems, ValueComparator); // to sort with
    //                                                         Comparator
}

class Item implements Comparable<Item> {
    String name;
    int value;

    public Item(String name, int value) {
        this.name = name;
        this.value = value;
    }

    @Override
    public int compareTo(Item other) {
        return Integer.compare(this.value, other.value);
        // return -1 * Integer.compare(this.value, other.value); in case you 
                                                     //need descending order

    }

    @Override
    public String toString() {
        return name + " " + value;
    }

}

answered Aug 15, 2017 at 4:03

Kedar Tokekar

4183 silver badges11 bronze badges

1 Comment

Zabuzard Over a year ago

Note that since Java 8 Comparator.comparing(Item::getValue) quickly and compactly yields the desired Comparator object. Append a reversed() call if the reversed logic is needed.

Collectives™ on Stack Overflow

Doing a Selection sort on an ArrayList

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related