java中TreeSet集合如何实现元素的判重

 /*
 看一下部分的TreeSet源码....
 public class TreeSet<E> extends AbstractSet<E>
     implements NavigableSet<E>, Cloneable, java.io.Serializable
 {
     private transient NavigableMap<E,Object> m;
     //NavigableMap继承SortedMap， 二者都是接口，在TreeMap中有实现
     private static final Object PRESENT = new Object();

     TreeSet(NavigableMap<E,Object> m) {
         this.m = m;
     }
     ////第一种构造方法
     public TreeSet(Comparator<? super E> comparator) {
         this(new TreeMap<>(comparator));
     }
     ////第二种构造方法
     public TreeSet() {
         this(new TreeMap<E,Object>());
     }
     ..........
     public boolean add(E e) {
         return m.put(e, PRESENT)==null;

     /*
         再看一下 TreeMap 中是如何实现的 put（）函数的
         public V put(K key, V value) {
         Entry<K,V> t = root;
         if (t == null) {
             compare(key, key); // type (and possibly null) check

             root = new Entry<>(key, value, null);
             size = 1;
             modCount++;
             return null;
         }
         int cmp;
         Entry<K,V> parent;
         // split comparator and comparable paths
         Comparator<? super K> cpr = comparator;
         if (cpr != null) {
             do {
                 parent = t;
                 cmp = cpr.compare(key, t.key);
                 if (cmp < 0)
                     t = t.left;
                 else if (cmp > 0)
                     t = t.right;
                 else
                     return t.setValue(value);
             } while (t != null);
         }
         else {
             if (key == null)
                 throw new NullPointerException();
             Comparable<? super K> k = (Comparable<? super K>) key;
             do {
                 parent = t;
                 cmp = k.compareTo(t.key);
                 if (cmp < 0)
                     t = t.left;
                 else if (cmp > 0)
                     t = t.right;
                 else
                     return t.setValue(value);
             } while (t != null);
         }
         Entry<K,V> e = new Entry<>(key, value, parent);
         if (cmp < 0)
             parent.left = e;
         else
             parent.right = e;
         fixAfterInsertion(e);
         size++;
         modCount++;
         return null;
     }
     */
     }
 }

 也就是说TreeSet内部实现使用TreeMap这个类来完成的
 TreeSet的内部实现元素之间是否相等？
 如果指定了Comparator（也就是利用第一种构造方法）, 那么就用其中的compare方法进行比较
 否则就用Comparable中的compareTo()方法进行元素的比较
 */

 import java.util.*;
 public class CompTest{
     public static void main(String args[]){
         Set<myClass> st = new TreeSet<myClass>();
         st.add(new myClass(1, "fd"));
         st.add(new myClass(2, "fff"));
         st.add(new myClass(2, "tttt"));
         st.add(new myClass(1, "fd"));

         for(Iterator<myClass> it = st.iterator(); it.hasNext();)
             System.out.println(it.next());
     }
 }

 class myClass implements Comparable<myClass>{

    public int x;
    public String name;
    public myClass(int x, String name){
        this.x=x;
        this.name=name;
    }
    public int compareTo(myClass tmp){
        if(this.x==tmp.x)
           return this.name.compareTo(tmp.name);
        else return this.x-tmp.x;
    }

    public String toString(){
       return x+" "+name;
    }
 }