Question

I want to go over the objects inside my TreeSet, I can do it by making an array using toArray but I don’t need to go over all of the objects in the Set.

How can I go over the objects in the Set (starting with the first than the second etc’) ?

And another small question about TreeSet : Can I keep the objects in the TreeSet sorted (so the first object will be with the smallest key etc’) ?

edit: say I have a class myInt (with int myInteger) and I want to use it in TreeSet with a different oredering than the natural one, what do I need to define in my class (myInt) to do this ?

Answer 1

How can I go over the objects in the Set

The easiest way to iterate over the items of the set is like so:

SortedSet<T> set = new TreeSet<T>();
for (T elem : set) {
  // use elem
}

Can I keep the objects in the TreeSet sorted

TreeSet is automatically sorted, so you don’t need to do anything.

I have a class MyInt (with int myInteger) and I want to use it in TreeSet with a different ordering than the natural one

You have two options:

Option 1: Make it implement Comparable<MyInt>:

public class MyInt implements Comparable<MyInt> {
   public int compareTo(MyInt o) {
     // return -1 if `this` is less than `o`
     //         0 if `this` is equal to `o`
     //         1 of `this` is greater than `o`
   }
}

Option 2: Supply a Comparator<MyInt> when constructing the TreeSet:

public class MyIntCmp implements Comparator<MyInt> {
  // implement compare() and equals() as per Comparator javadoc
}
SortedSet<T> set = new TreeSet<T>(new MyIntCmp());