1 /*  2 看一下部分的TreeSet源码....  3 public class TreeSet
     
       extends AbstractSet
      
         4     implements NavigableSet
       
        , Cloneable, java.io.Serializable  5 {  6     private transient NavigableMap
        
          m;  7     //NavigableMap继承SortedMap， 二者都是接口，在TreeMap中有实现  8     private static final Object PRESENT = new Object();  9  10     TreeSet(NavigableMap
         
           m) { 11         this.m = m; 12     } 13     第一种构造方法 14     public TreeSet(Comparator
           comparator) { 15         this(new TreeMap<>(comparator)); 16     } 17     第二种构造方法 18     public TreeSet() { 19         this(new TreeMap
          
           ()); 20 } 21 .......... 22 public boolean add(E e) { 23 return m.put(e, PRESENT)==null; 24 25 /* 26 再看一下 TreeMap 中是如何实现的 put（）函数的 27 public V put(K key, V value) { 28 Entry
           
             t = root; 29 if (t == null) { 30 compare(key, key); // type (and possibly null) check 31 32 root = new Entry<>(key, value, null); 33 size = 1; 34 modCount++; 35 return null; 36 } 37 int cmp; 38 Entry
            
              parent; 39 // split comparator and comparable paths 40 Comparator
              cpr = comparator; 41 if (cpr != null) { 42 do { 43 parent = t; 44 cmp = cpr.compare(key, t.key); 45 if (cmp < 0) 46 t = t.left; 47 else if (cmp > 0) 48 t = t.right; 49 else 50 return t.setValue(value); 51 } while (t != null); 52 } 53 else { 54 if (key == null) 55 throw new NullPointerException(); 56 Comparable
              k = (Comparable
             ) key; 57 do { 58 parent = t; 59 cmp = k.compareTo(t.key); 60 if (cmp < 0) 61 t = t.left; 62 else if (cmp > 0) 63 t = t.right; 64 else 65 return t.setValue(value); 66 } while (t != null); 67 } 68 Entry
             
               e = new Entry<>(key, value, parent); 69 if (cmp < 0) 70 parent.left = e; 71 else 72 parent.right = e; 73 fixAfterInsertion(e); 74 size++; 75 modCount++; 76 return null; 77 } 78 */ 79 } 80 } 81 82 也就是说TreeSet内部实现使用TreeMap这个类来完成的 83 TreeSet的内部实现元素之间是否相等？ 84 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 85 否则就用Comparable中的compareTo()方法进行元素的比较 86 */ 87 88 import java.util.*; 89 public class CompTest{ 90 public static void main(String args[]){ 91 Set
              
                st = new TreeSet
               
                (); 92 st.add(new myClass(1, "fd")); 93 st.add(new myClass(2, "fff")); 94 st.add(new myClass(2, "tttt")); 95 st.add(new myClass(1, "fd")); 96 97 for(Iterator
                
                  it = st.iterator(); it.hasNext();) 98 System.out.println(it.next()); 99 }100 }101 102 class myClass implements Comparable
                 
                  {103 104 public int x;105 public String name;106 public myClass(int x, String name){107 this.x=x;108 this.name=name;109 }110 public int compareTo(myClass tmp){111 if(this.x==tmp.x)112 return this.name.compareTo(tmp.name);113 else return this.x-tmp.x;114 }115 116 public String toString(){117 return x+" "+name;118 }119 }