I am trying to sort an ordered list with objects, but I am not sure how to do it. I am putting in objects with a population(integer) associated with it. How would I make a method to sort the list so that the object with the lowest population would be first, and the object with the highest population would be last.
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Needs code. Most folks use `Arrays.sort()` or `Collections.sort()` – markspace Apr 05 '20 at 20:05
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Also, what version of Java are you using? – markspace Apr 05 '20 at 20:05
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https://stackoverflow.com/questions/5932720/how-to-sort-an-attribute-of-an-object-using-collections Found by Google "java sort by attribute" – markspace Apr 05 '20 at 20:06
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E.g. `cities.sort(Comparator.comparingInt(City::getPopulation))` – Andreas Apr 05 '20 at 20:21
1 Answers
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"For any class to support natural ordering, it should implement the Comparable interface and override it’s compareTo() method. It must return a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object."
public class YourObject implements Comparable<YourObject> {
int population;
YourObject(int pop) {
population = pop;
}
@Override
public int compareTo(YourObject other)
{
return this.population - other.population;
}
}
then you can use Collections.sort(list) on your list
Miłosz Tomkiel
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1Don't use subtraction to sort by `int` values. Use [`Integer.compare(int x, int y)`](https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html#compare-int-int-). – Andreas Apr 05 '20 at 20:19