java中TreeSet集合如何實現元素的判重

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

    TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }
    第一種構造方法
    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
    }
    第二種構造方法
    public TreeSet() {
        this(new TreeMap<E,Object>());
    }
    ..........
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;

    /*
        再看一下 TreeMap 中是如何實現的 put（）函數的
        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;
    }
    */
    }
}

也就是說TreeSet內部實現使用TreeMap這個類來完成的
TreeSet的內部實現元素之間是否相等？
如果指定了Comparator（也就是利用第一種構造方法）, 那么就用其中的compare方法進行比較
否則就用Comparable中的compareTo()方法進行元素的比較
*/

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;
   }
}

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