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javacomparatorcomparable

How to make my own generic structure to have dynamic comparator

I want to know how i can override compareTo method in class which implements Comparable

my structure Tree is declared like this

public class Tree<T extends Comparable<T>>

and class which used that structure is Plane that looks like that

public class Plane implements Comparable<Plane>

with override compareTo method,

the thing is if i want create a tree with default comparator i can do that easily with this 

Tree<Plane> planes = new Tree<Plane>();

but i want have another tree structure with planes and with different compareTo method, how i can override that method in plane?

Thanks

Solution

  • Define an overloaded constructor:

    public Tree() {
  this(Comparator.naturalOrder());
}

public Tree(Comparator<? super T> comparator) {
  this.comparator = comparator; // store in a field
}

    And then use the comparator instead of the compareTo method on the tree elements.

    But note that the ability to supply a comparator removes the restriction that T extends Comparable<T> (which is better as T extends Comparable<? super T> anyway).

    But in such a case, you can't have a default constructor type-safely. You would either need to require a comparator always to be passed; or provide a static factory method to create a naturally-ordered tree:

    static <T extends Comparable<? super T>> Tree<T> withNaturalOrder() {
  return new Tree<>(Comparator.naturalOrder());
}

    And invoke like

    Tree<String> tree = Tree.withNaturalOrder();