Java-TreeSet源码分析及示例
纸上得来终觉浅，绝知此事要躬行 --陆游
问渠那得清如许，为有源头活水来 --朱熹
TreeSet是一个有序的集合，它的作用是提供有序的Set集合。它继承了AbstractSet抽象类，实现了NavigableSet<E>，Cloneable，Serializable接口。TreeSet是基于TreeMap实现的，TreeSet的元素支持2种排序方式：自然排序或者根据提供的Comparator进行排序。
TreeSet的接口依赖图：
从图中可以看出：
（1）TreeSet继承于AbstractSet，并且实现了NavigableSet接口。
（2）TreeSet是一个包含有序的且没有重复元素的集合，通过TreeMap实现。
TreeSet的主要函数：
boolean add(E object)TreeSet遍历方式：
boolean addAll(Collection<? extends E> collection)
void clear()
Object clone()
boolean contains(Object object)
E first()
boolean isEmpty()
E last()
E pollFirst()
E pollLast()
E lower(E e)
E floor(E e)
E ceiling(E e)
E higher(E e)
boolean remove(Object object)
int size()
Comparator<? super E> comparator()
Iterator<E> iterator()
Iterator<E> descendingIterator()
SortedSet<E> headSet(E end)
NavigableSet<E> descendingSet()
NavigableSet<E> headSet(E end, boolean endInclusive)
SortedSet<E> subSet(E start, E end)
NavigableSet<E> subSet(E start, boolean startInclusive, E end, boolean endInclusive)
NavigableSet<E> tailSet(E start, boolean startInclusive)
SortedSet<E> tailSet(E start)
（1）迭代器顺序遍历方式：
for(Iterator iter = set.iterator(); iter.hasNext(); )（2）迭代器倒序遍历方式：
{
iter.next();
}
for(Iterator iter = set.descendingIterator(); iter.hasNext(); )（3）foreach遍历HashSet
{
iter.next();
}
String[] arr = (String[])set.toArray(new String[0]);TreeSet示例代码：
for (String str:arr)
{
System.out.printf("for each : %s\n", str);
}
public class Hello {基于Java8的TreeSet源码分析：
public static void main(String[] args) {
testTreeSetAPIs();
}
// 测试TreeSet的api
public static void testTreeSetAPIs() {
String val;
// 新建TreeSet
TreeSet tSet = new TreeSet();
// 将元素添加到TreeSet中
tSet.add("aaa");
// Set中不允许重复元素，所以只会保存一个“aaa”
tSet.add("aaa");
tSet.add("bbb");
tSet.add("eee");
tSet.add("ddd");
tSet.add("ccc");
System.out.println("TreeSet:"+tSet);
// 打印TreeSet的实际大小
System.out.printf("size : %d\n", tSet.size());
// 导航方法
// floor(小于、等于)
System.out.printf("floor bbb: %s\n", tSet.floor("bbb"));
// lower(小于)
System.out.printf("lower bbb: %s\n", tSet.lower("bbb"));
// ceiling(大于、等于)
System.out.printf("ceiling bbb: %s\n", tSet.ceiling("bbb"));
System.out.printf("ceiling eee: %s\n", tSet.ceiling("eee"));
// ceiling(大于)
System.out.printf("higher bbb: %s\n", tSet.higher("bbb"));
// subSet()
System.out.printf("subSet(aaa, true, ccc, true): %s\n", tSet.subSet("aaa", true, "ccc", true));
System.out.printf("subSet(aaa, true, ccc, false): %s\n", tSet.subSet("aaa", true, "ccc", false));
System.out.printf("subSet(aaa, false, ccc, true): %s\n", tSet.subSet("aaa", false, "ccc", true));
System.out.printf("subSet(aaa, false, ccc, false): %s\n", tSet.subSet("aaa", false, "ccc", false));
// headSet()
System.out.printf("headSet(ccc, true): %s\n", tSet.headSet("ccc", true));
System.out.printf("headSet(ccc, false): %s\n", tSet.headSet("ccc", false));
// tailSet()
System.out.printf("tailSet(ccc, true): %s\n", tSet.tailSet("ccc", true));
System.out.printf("tailSet(ccc, false): %s\n", tSet.tailSet("ccc", false));
// 删除“ccc”
tSet.remove("ccc");
// 将Set转换为数组
String[] arr = (String[])tSet.toArray(new String[0]);
for (String str:arr)
System.out.printf("for each : %s\n", str);
// 打印TreeSet
System.out.printf("TreeSet:%s\n", tSet);
// 遍历TreeSet
for(Iterator iter = tSet.iterator(); iter.hasNext(); ) {
System.out.printf("iter : %s\n", iter.next());
}
// 删除并返回第一个元素
val = (String)tSet.pollFirst();
System.out.printf("pollFirst=%s, set=%s\n", val, tSet);
// 删除并返回最后一个元素
val = (String)tSet.pollLast();
System.out.printf("pollLast=%s, set=%s\n", val, tSet);
// 清空HashSet
tSet.clear();
// 输出HashSet是否为空
System.out.printf("%s\n", tSet.isEmpty()?"set is empty":"set is not empty");
}
}
public class Hello { public static void main(String[] args) { testTreeSetAPIs(); } // 测试TreeSet的api public static void testTreeSetAPIs() { String val; // 新建TreeSet TreeSet tSet = new TreeSet(); // 将元素添加到TreeSet中 tSet.add("aaa"); // Set中不允许重复元素，所以只会保存一个“aaa” tSet.add("aaa"); tSet.add("bbb"); tSet.add("eee"); tSet.add("ddd"); tSet.add("ccc"); System.out.println("TreeSet:"+tSet); // 打印TreeSet的实际大小 System.out.printf("size : %d\n", tSet.size()); // 导航方法 // floor(小于、等于) System.out.printf("floor bbb: %s\n", tSet.floor("bbb")); // lower(小于) System.out.printf("lower bbb: %s\n", tSet.lower("bbb")); // ceiling(大于、等于) System.out.printf("ceiling bbb: %s\n", tSet.ceiling("bbb")); System.out.printf("ceiling eee: %s\n", tSet.ceiling("eee")); // ceiling(大于) System.out.printf("higher bbb: %s\n", tSet.higher("bbb")); // subSet() System.out.printf("subSet(aaa, true, ccc, true): %s\n", tSet.subSet("aaa", true, "ccc", true)); System.out.printf("subSet(aaa, true, ccc, false): %s\n", tSet.subSet("aaa", true, "ccc", false)); System.out.printf("subSet(aaa, false, ccc, true): %s\n", tSet.subSet("aaa", false, "ccc", true)); System.out.printf("subSet(aaa, false, ccc, false): %s\n", tSet.subSet("aaa", false, "ccc", false)); // headSet() System.out.printf("headSet(ccc, true): %s\n", tSet.headSet("ccc", true)); System.out.printf("headSet(ccc, false): %s\n", tSet.headSet("ccc", false)); // tailSet() System.out.printf("tailSet(ccc, true): %s\n", tSet.tailSet("ccc", true)); System.out.printf("tailSet(ccc, false): %s\n", tSet.tailSet("ccc", false)); // 删除“ccc” tSet.remove("ccc"); // 将Set转换为数组 String[] arr = (String[])tSet.toArray(new String[0]); for (String str:arr) System.out.printf("for each : %s\n", str); // 打印TreeSet System.out.printf("TreeSet:%s\n", tSet); // 遍历TreeSet for(Iterator iter = tSet.iterator(); iter.hasNext(); ) { System.out.printf("iter : %s\n", iter.next()); } // 删除并返回第一个元素 val = (String)tSet.pollFirst(); System.out.printf("pollFirst=%s, set=%s\n", val, tSet); // 删除并返回最后一个元素 val = (String)tSet.pollLast(); System.out.printf("pollLast=%s, set=%s\n", val, tSet); // 清空HashSet tSet.clear(); // 输出HashSet是否为空 System.out.printf("%s\n", tSet.isEmpty()?"set is empty":"set is not empty"); } }基于Java8的TreeSet源码分析：
public class TreeSet<E> extends AbstractSet<E> implements NavigableSet<E>, Cloneable, java.io.Serializable { /** * The backing map. */ private transient NavigableMap<E,Object> m; // Dummy value to associate with an Object in the backing Map private static final Object PRESENT = new Object(); /** * Constructs a set backed by the specified navigable map. */ //构造函数 TreeSet(NavigableMap<E,Object> m) { this.m = m; } /** * Constructs a new, empty tree set, sorted according to the * natural ordering of its elements. All elements inserted into * the set must implement the {@link Comparable} interface. * Furthermore, all such elements must be <i>mutually * comparable</i>: {@code e1.compareTo(e2)} must not throw a * {@code ClassCastException} for any elements {@code e1} and * {@code e2} in the set. If the user attempts to add an element * to the set that violates this constraint (for example, the user * attempts to add a string element to a set whose elements are * integers), the {@code add} call will throw a * {@code ClassCastException}. */ //构造空的tree set 根据自然顺序对元素进行排序 public TreeSet() { this(new TreeMap<E,Object>()); } /** * Constructs a new, empty tree set, sorted according to the specified * comparator. All elements inserted into the set must be <i>mutually * comparable</i> by the specified comparator: {@code comparator.compare(e1, * e2)} must not throw a {@code ClassCastException} for any elements * {@code e1} and {@code e2} in the set. If the user attempts to add * an element to the set that violates this constraint, the * {@code add} call will throw a {@code ClassCastException}. * * @param comparator the comparator that will be used to order this set. * If {@code null}, the {@linkplain Comparable natural * ordering} of the elements will be used. */ //构造函数，根据特定的比较器对元素进行排序 public TreeSet(Comparator<? super E> comparator) { this(new TreeMap<>(comparator)); } //构造函数，参数为已有的集合 public TreeSet(Collection<? extends E> c) { this(); addAll(c); } /** * Constructs a new tree set containing the same elements and * using the same ordering as the specified sorted set. * * @param s sorted set whose elements will comprise the new set * @throws NullPointerException if the specified sorted set is null */ //构造函数，参数为已经排序的集合 public TreeSet(SortedSet<E> s) { this(s.comparator()); addAll(s); } /** * Returns an iterator over the elements in this set in ascending order. * * @return an iterator over the elements in this set in ascending order */ //返回顺序排好的迭代器 public Iterator<E> iterator() { return m.navigableKeySet().iterator(); } /** * Returns an iterator over the elements in this set in descending order. * * @return an iterator over the elements in this set in descending order * @since 1.6 */ //返回倒序排好的迭代器 public Iterator<E> descendingIterator() { return m.descendingKeySet().iterator(); } /** * @since 1.6 */ //倒序排好的集合 public NavigableSet<E> descendingSet() { return new TreeSet<>(m.descendingMap()); } /** * Returns the number of elements in this set (its cardinality). * * @return the number of elements in this set (its cardinality) */ //大小 public int size() { return m.size(); } /** * Returns {@code true} if this set contains no elements. * * @return {@code true} if this set contains no elements */ //判断是否为空 public boolean isEmpty() { return m.isEmpty(); } /** * Returns {@code true} if this set contains the specified element. * More formally, returns {@code true} if and only if this set * contains an element {@code e} such that * <tt>(o==null ? e==null : o.equals(e))</tt>. * * @param o object to be checked for containment in this set * @return {@code true} if this set contains the specified element * @throws ClassCastException if the specified object cannot be compared * with the elements currently in the set * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements */ //判断是否包含某个值 public boolean contains(Object o) { return m.containsKey(o); } /** * Adds the specified element to this set if it is not already present. * More formally, adds the specified element {@code e} to this set if * the set contains no element {@code e2} such that * <tt>(e==null ? e2==null : e.equals(e2))</tt>. * If this set already contains the element, the call leaves the set * unchanged and returns {@code false}. * * @param e element to be added to this set * @return {@code true} if this set did not already contain the specified * element * @throws ClassCastException if the specified object cannot be compared * with the elements currently in this set * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements */ //添加元素 public boolean add(E e) { return m.put(e, PRESENT)==null; } /** * Removes the specified element from this set if it is present. * More formally, removes an element {@code e} such that * <tt>(o==null ? e==null : o.equals(e))</tt>, * if this set contains such an element. Returns {@code true} if * this set contained the element (or equivalently, if this set * changed as a result of the call). (This set will not contain the * element once the call returns.) * * @param o object to be removed from this set, if present * @return {@code true} if this set contained the specified element * @throws ClassCastException if the specified object cannot be compared * with the elements currently in this set * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements */ //删除某个对象 public boolean remove(Object o) { return m.remove(o)==PRESENT; } /** * Removes all of the elements from this set. * The set will be empty after this call returns. */ //清空对象 public void clear() { m.clear(); } /** * Adds all of the elements in the specified collection to this set. * * @param c collection containing elements to be added to this set * @return {@code true} if this set changed as a result of the call * @throws ClassCastException if the elements provided cannot be compared * with the elements currently in the set * @throws NullPointerException if the specified collection is null or * if any element is null and this set uses natural ordering, or * its comparator does not permit null elements */ //添加已经存在的元素到集合中 public boolean addAll(Collection<? extends E> c) { // Use linear-time version if applicable if (m.size()==0 && c.size() > 0 && c instanceof SortedSet && m instanceof TreeMap) { SortedSet<? extends E> set = (SortedSet<? extends E>) c; TreeMap<E,Object> map = (TreeMap<E, Object>) m; Comparator<?> cc = set.comparator(); Comparator<? super E> mc = map.comparator(); if (cc==mc || (cc != null && cc.equals(mc))) { map.addAllForTreeSet(set, PRESENT); return true; } } return super.addAll(c); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if {@code fromElement} or {@code toElement} * is null and this set uses natural ordering, or its comparator * does not permit null elements * @throws IllegalArgumentException {@inheritDoc} * @since 1.6 */ //截取集合从fromElement到toElement public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { return new TreeSet<>(m.subMap(fromElement, fromInclusive, toElement, toInclusive)); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if {@code toElement} is null and * this set uses natural ordering, or its comparator does * not permit null elements * @throws IllegalArgumentException {@inheritDoc} * @since 1.6 */ //获得从集合开始到toElement的元素 public NavigableSet<E> headSet(E toElement, boolean inclusive) { return new TreeSet<>(m.headMap(toElement, inclusive)); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if {@code fromElement} is null and * this set uses natural ordering, or its comparator does * not permit null elements * @throws IllegalArgumentException {@inheritDoc} * @since 1.6 */ //获得从fromElement开始到结尾的元素 public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { return new TreeSet<>(m.tailMap(fromElement, inclusive)); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if {@code fromElement} or * {@code toElement} is null and this set uses natural ordering, * or its comparator does not permit null elements * @throws IllegalArgumentException {@inheritDoc} */ //截取元素，从fromElement到toElement public SortedSet<E> subSet(E fromElement, E toElement) { return subSet(fromElement, true, toElement, false); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if {@code toElement} is null * and this set uses natural ordering, or its comparator does * not permit null elements * @throws IllegalArgumentException {@inheritDoc} */ //从头开始到toElement，不包含toElement public SortedSet<E> headSet(E toElement) { return headSet(toElement, false); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if {@code fromElement} is null * and this set uses natural ordering, or its comparator does * not permit null elements * @throws IllegalArgumentException {@inheritDoc} */ //从fromElement开始(包含)到结尾 public SortedSet<E> tailSet(E fromElement) { return tailSet(fromElement, true); } //比较器 public Comparator<? super E> comparator() { return m.comparator(); } /** * @throws NoSuchElementException {@inheritDoc} */ //得到第一个元素 public E first() { return m.firstKey(); } /** * @throws NoSuchElementException {@inheritDoc} */ //获得最后一个元素 public E last() { return m.lastKey(); } // NavigableSet API methods /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements * @since 1.6 */ //比e小的一个元素 public E lower(E e) { return m.lowerKey(e); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements * @since 1.6 */ //比e小于等于 public E floor(E e) { return m.floorKey(e); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements * @since 1.6 */ //比e大于等于 public E ceiling(E e) { return m.ceilingKey(e); } /** * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * and this set uses natural ordering, or its comparator * does not permit null elements * @since 1.6 */ //比e大的 public E higher(E e) { return m.higherKey(e); } /** * @since 1.6 */ //获得第一个元素删除并返回 public E pollFirst() { Map.Entry<E,?> e = m.pollFirstEntry(); return (e == null) ? null : e.getKey(); } /** * @since 1.6 */ //获得最后一个元素删除并返回 public E pollLast() { Map.Entry<E,?> e = m.pollLastEntry(); return (e == null) ? null : e.getKey(); } /** * Returns a shallow copy of this {@code TreeSet} instance. (The elements * themselves are not cloned.) * * @return a shallow copy of this set */ //浅拷贝 @SuppressWarnings("unchecked") public Object clone() { TreeSet<E> clone; try { clone = (TreeSet<E>) super.clone(); } catch (CloneNotSupportedException e) { throw new InternalError(e); } clone.m = new TreeMap<>(m); return clone; } /** * Save the state of the {@code TreeSet} instance to a stream (that is, * serialize it). * * @serialData Emits the comparator used to order this set, or * {@code null} if it obeys its elements' natural ordering * (Object), followed by the size of the set (the number of * elements it contains) (int), followed by all of its * elements (each an Object) in order (as determined by the * set's Comparator, or by the elements' natural ordering if * the set has no Comparator). */ //序列化写对象 private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { // Write out any hidden stuff s.defaultWriteObject(); // Write out Comparator s.writeObject(m.comparator()); // Write out size s.writeInt(m.size()); // Write out all elements in the proper order. for (E e : m.keySet()) s.writeObject(e); } /** * Reconstitute the {@code TreeSet} instance from a stream (that is, * deserialize it). */ //序列化读对象 private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { // Read in any hidden stuff s.defaultReadObject(); // Read in Comparator @SuppressWarnings("unchecked") Comparator<? super E> c = (Comparator<? super E>) s.readObject(); // Create backing TreeMap TreeMap<E,Object> tm = new TreeMap<>(c); m = tm; // Read in size int size = s.readInt(); tm.readTreeSet(size, s, PRESENT); } /** * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> * and <em>fail-fast</em> {@link Spliterator} over the elements in this * set. * * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, * {@link Spliterator#DISTINCT}, {@link Spliterator#SORTED}, and * {@link Spliterator#ORDERED}. Overriding implementations should document * the reporting of additional characteristic values. * * <p>The spliterator's comparator (see * {@link java.util.Spliterator#getComparator()}) is {@code null} if * the tree set's comparator (see {@link #comparator()}) is {@code null}. * Otherwise, the spliterator's comparator is the same as or imposes the * same total ordering as the tree set's comparator. * * @return a {@code Spliterator} over the elements in this set * @since 1.8 */ public Spliterator<E> spliterator() { return TreeMap.keySpliteratorFor(m); } private static final long serialVersionUID = -2479143000061671589L; }