Hash table and linked list implementation of the Set interface, + * with predictable iteration order. This implementation differs from + * HashSet in that it maintains a doubly-linked list running through + * all of its entries. This linked list defines the iteration ordering, + * which is the order in which elements were inserted into the set + * (insertion-order). Note that insertion order is not affected + * if an element is re-inserted into the set. (An element e + * is reinserted into a set s if s.add(e) is invoked when + * s.contains(e) would return true immediately prior to + * the invocation.) + * + *
This implementation spares its clients from the unspecified, generally + * chaotic ordering provided by {@link HashSet}, without incurring the + * increased cost associated with {@link TreeSet}. It can be used to + * produce a copy of a set that has the same order as the original, regardless + * of the original set's implementation: + *
+ * void foo(Set s) {
+ * Set copy = new LinkedHashSet(s);
+ * ...
+ * }
+ *
+ * This technique is particularly useful if a module takes a set on input,
+ * copies it, and later returns results whose order is determined by that of
+ * the copy. (Clients generally appreciate having things returned in the same
+ * order they were presented.)
+ *
+ * This class provides all of the optional Set operations, and + * permits null elements. Like HashSet, it provides constant-time + * performance for the basic operations (add, contains and + * remove), assuming the hash function disperses elements + * properly among the buckets. Performance is likely to be just slightly + * below that of HashSet, due to the added expense of maintaining the + * linked list, with one exception: Iteration over a LinkedHashSet + * requires time proportional to the size of the set, regardless of + * its capacity. Iteration over a HashSet is likely to be more + * expensive, requiring time proportional to its capacity. + * + *
A linked hash set has two parameters that affect its performance: + * initial capacity and load factor. They are defined precisely + * as for HashSet. Note, however, that the penalty for choosing an + * excessively high value for initial capacity is less severe for this class + * than for HashSet, as iteration times for this class are unaffected + * by capacity. + * + *
Note that this implementation is not synchronized. + * If multiple threads access a linked hash set concurrently, and at least + * one of the threads modifies the set, it must be synchronized + * externally. This is typically accomplished by synchronizing on some + * object that naturally encapsulates the set. + * + * If no such object exists, the set should be "wrapped" using the + * {@link Collections#synchronizedSet Collections.synchronizedSet} + * method. This is best done at creation time, to prevent accidental + * unsynchronized access to the set:
+ * Set s = Collections.synchronizedSet(new LinkedHashSet(...));+ * + *
The iterators returned by this class's iterator method are + * fail-fast: if the set is modified at any time after the iterator + * is created, in any way except through the iterator's own remove + * method, the iterator will throw a {@link ConcurrentModificationException}. + * Thus, in the face of concurrent modification, the iterator fails quickly + * and cleanly, rather than risking arbitrary, non-deterministic behavior at + * an undetermined time in the future. + * + *
Note that the fail-fast behavior of an iterator cannot be guaranteed + * as it is, generally speaking, impossible to make any hard guarantees in the + * presence of unsynchronized concurrent modification. Fail-fast iterators + * throw ConcurrentModificationException on a best-effort basis. + * Therefore, it would be wrong to write a program that depended on this + * exception for its correctness: the fail-fast behavior of iterators + * should be used only to detect bugs. + * + *
This class is a member of the
+ *
+ * Java Collections Framework.
+ *
+ * @param