public class TreeSet<E>{
    
    private static final Object PRESENT = new Object();
    //1-1. 调用无参构造函数
    public TreeSet() {
        this(new TreeMap<E,Object>());
    }
    
    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
    }
    
    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }
    
    //实际调用的是TreeMap的put方法
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }
    
    
    //-------------以下是TreeMap的源码------------------
    
    private final Comparator<? super K> comparator;
    
    private transient Entry<K,V> root;
    
    private transient int size = 0;
    
    private transient int modCount = 0;
    
    
    
    //1-2.没有传入外部比较器，外部比较器为空，使用元素自己实现的内部比较器
    public TreeMap() {
        comparator = null;
    }
    
    public TreeMap(Comparator<? super K> comparator) {
        this.comparator = comparator;
    }
    
    //2-1.调用put方法 key=Student{id=1, name=‘lili‘} value=PRESENT
    //3-1.添加第二个元素 key=Student{id=2, name=‘huahua‘}
    //4-1.添加第三个元素 key=Student{id=3, name=‘xixi‘}
    public V put(K key, V value) {
        //2-2.t = null
        //3-2. t= root=Student{id=1, name=‘lili‘}
        //4-2. t= root=Student{id=1, name=‘lili‘}
        Entry<K,V> t = root;
        if (t == null) {
            //2-3.进入compare方法 key=key=Student{id=1, name=‘lili‘}
            //compare(key,key) 3种可能，要么>0的数，要么=0，要么<0的数
            compare(key, key); // type (and possibly null) check

            //2-4.给root赋值  root=Student{id=1, name=‘lili‘}
            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            //2-5.添加第一个元素结束
            return null;
        }
        int cmp;
        Entry<K,V> parent;
        // split comparator and comparable paths
        Comparator<? super K> cpr = comparator;
        
        //外部比较器除了compara方法参数是两个之外，其余都一样。
        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 {
            //3-3.TreeMap不能添加null
            if (key == null)
                throw new NullPointerException();
            @SuppressWarnings("unchecked")
                Comparable<? super K> k = (Comparable<? super K>) key;
            do {
                //4-5.parent=Student{id=2, name=‘huahua‘}
                parent = t;
                //3-4.当前元素=Student{id=2, name=‘huahua‘}跟root=Student{id=1, name=‘lili‘}比较
                //4-3.当前元素=Student{id=3, name=‘xixi‘}跟root=Student{id=1, name=‘lili‘}比较
                //4-6.当前元素=Student{id=3, name=‘xixi‘}跟t=Student{id=2, name=‘huahua‘}比较
                cmp = k.compareTo(t.key);
                if (cmp < 0)
                    //3-5.如果当前元素小，t=null
                    t = t.left;
                else if (cmp > 0)
                    //3-6.当前元素>root，t=t.right=null
                    //4-4. 当前元素>root, t=t.right=Student{id=2, name=‘huahua‘}
                    //4-7.当前元素>t,t=t.right=null
                    t = t.right;
                else
                    //返回老值
                    return t.setValue(value);
            } while (t != null);
        }
        //3-7.创建当前元素Student{id=2, name=‘huahua‘}的Entry实例
        //4-8.创建当前元素Student{id=3, name=‘xixi‘}的Entry实例
        Entry<K,V> e = new Entry<>(key, value, parent);
        if (cmp < 0)
            //3-8.如果当前元素小，就放到root的左边
            parent.left = e;
        else
            //3-9.如果当前元素大，就放到root的右边
            //4-9.当前元素Student{id=3, name=‘xixi‘}放到parentStudent{id=2, name=‘huahua‘}的右边
            parent.right = e;
        //3-10. 红黑树的过程
        //4-10. 红黑树后改变形态，下一次root会变，以此类推
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }
    
    //有外部比较器时用外部比较器，没有外部比较器用要插入的元素的内部比较器，并且实现compareTo方法
    final int compare(Object k1, Object k2) {
        return comparator==null ? ((Comparable<? super K>)k1).compareTo((K)k2)
            : comparator.compare((K)k1, (K)k2);
    }
        
    private void fixAfterInsertion(Entry<K,V> x) {
        x.color = RED;

        while (x != null && x != root && x.parent.color == RED) {
            if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {
                Entry<K,V> y = rightOf(parentOf(parentOf(x)));
                if (colorOf(y) == RED) {
                    setColor(parentOf(x), BLACK);
                    setColor(y, BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    x = parentOf(parentOf(x));
                } else {
                    if (x == rightOf(parentOf(x))) {
                        x = parentOf(x);
                        rotateLeft(x);
                    }
                    setColor(parentOf(x), BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    rotateRight(parentOf(parentOf(x)));
                }
            } else {
                Entry<K,V> y = leftOf(parentOf(parentOf(x)));
                if (colorOf(y) == RED) {
                    setColor(parentOf(x), BLACK);
                    setColor(y, BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    x = parentOf(parentOf(x));
                } else {
                    if (x == leftOf(parentOf(x))) {
                        x = parentOf(x);
                        rotateRight(x);
                    }
                    setColor(parentOf(x), BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    rotateLeft(parentOf(parentOf(x)));
                }
            }
        }
        root.color = BLACK;
    }
    
    //------------内部类Entry的源码-------------------------
    
    public V setValue(V value) {
            V oldValue = this.value;
            this.value = value;
            return oldValue;
        }
    
}