Sorting Arraylist by an object variable - sorting

Question

Any ideas on how to apply Collections.sort method to sort my arraylist by priority of each grocItem object within the itemData ArrayList?
public class GroceryProgram {
private final static int GROC_SIZE = 6;
private final List<ItemData> itemData = new ArrayList<ItemData>();
private void setUpList() {
Scanner keyboard = new Scanner(System.in);
for (int i = 0; i < GROC_SIZE; i++) {
System.out.print("\nEnter item name (" + i + ") : ");
String name = keyboard.next();
System.out.print("\nEnter the price of item (" + i + ") : ");
double cost = keyboard.nextDouble();
System.out.print("\nEnter Priority Number (" + i + ") : ");
int priority = keyboard.nextInt();
ItemData grocItem = new ItemData(name, cost, priority);
itemData.add(grocItem); // add grocery items to itemData ArrayList
Collections.sort(grocItem);
for (Int priority : priority) {
System.out.println(integer);

Answer 1

Call sort() with a Comparator. For example, a Comparator in ascending-order of priority could look like this.
Collections.sort( items, new Comparator<ItemData>() {
public int compare (ItemData o1, ItemData o2) {
int comp = o1.getPriority() - o2.getPriority();
return comp;
}
});
PS: 'itemData' is bad variable naming -- it would refer to a single item, not a list. 'groceryItems', 'stockItems' or 'itemList' would be better.
Variable names should enable you to speak in meaningful, clear, concise English about your software.
Hope this helps.

Answer 2

Could you use Collections.sort(List list, Comparator c) to deal with this? You could simply do the following :
Collections.sort(itemData, new Comparator() {
public int compare(Object o1, Object o2) {
// Return a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.
}
}

Answer 3

You can use custom comparator as below:
Collections.sort(itemData ,new PriorityComparator());
//print sorted arraylist,it will print the data in ascending order (low priority->high priority).feel free to modify if you want to go for descending order
System.out.println(itemData );
PriorityComparator class definition:
private static class PriorityComparator implements Comparator{
#Override
public int compare(ItemData object1, ItemData object2) {
return (object1.priority< object2.priority) ? -1: (object1.priority> object2.priority) ? 1:0 ;
}
}
Reference:
how-to-sort-arraylist-in-java-example
I hope it will be helpful !!