Java中的迭代器与集合
Iterator和Collection多次帮助和安慰了程序员。但是那里的用法和应用有很大的区别。
1. 迭代器
- 宣言
public interface Iterator
Type Parameters:
E - the type of elements returned by this iterator- Java中的 Collection 框架中使用迭代器来逐个检索元素。
- 方法总结
| Modifier and Type | Method | Description |
|---|---|---|
| default void | forEachRemaining(Consumer action) | Performs the given action for each remaining element until all elements have been processed or the action throws an exception. |
| boolean | hasNext() | Returns true if the iteration has more elements. |
| E | next() | Returns the next element in the iteration. |
| default void | remove() | Removes from the underlying collection the last element returned by this iterator (optional operation). |
2. 收藏
- 宣言：
public interface Collection extends Iterable
Type Parameters:
E - the type of elements returned by this iterator - 集合是一组表示为单个单元的单个对象。 Java提供了集合框架，它定义了几个类和接口来将一组对象表示为一个单元。
- 方法总结
| Modifier and Type | Method | Description |
|---|---|---|
| boolean | add(E e) | Ensures that this collection contains the specified element (optional operation). |
| boolean | addAll(Collection c) | Adds all of the elements in the specified collection to this collection (optional operation). |
| void | clear() | Removes all of the elements from this collection (optional operation). |
| boolean | contains(Object o) | Returns true if this collection contains the specified element. |
| boolean | containsAll(Collection c) | Returns true if this collection contains all of the elements in the specified collection. |
| boolean | equals(Object o) | Compares the specified object with this collection for equality. |
| int | hashCode() | Returns the hash code value for this collection. |
| boolean | isEmpty() | Returns true if this collection contains no elements. |
| Iterator | iterator() | Returns an iterator over the elements in this collection. |
| default Stream | parallelStream() | Returns a possibly parallel Stream with this collection as its source. |
| boolean | remove(Object o) | Removes a single instance of the specified element from this collection, if it is present (optional operation). |
| boolean | removeAll(Collection c) | Removes all of this collection’s elements that are also contained in the specified collection (optional operation). |
| default boolean | removeIf(Predicate filter) | Removes all of the elements of this collection that satisfy the given predicate. |
| boolean | retainAll(Collection c) | Retains only the elements in this collection that are contained in the specified collection (optional operation). |
| int | size() | Returns the number of elements in this collection. |
| default Spliterator | spliterator() | Creates a Spliterator over the elements in this collection. |
| default Stream | stream() | Returns a sequential Stream with this collection as its source. |
| Object[] | toArray() | Returns an array containing all of the elements in this collection. |
| T[] | toArray(T[] a) | Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. |
迭代器对比收藏
- 迭代器只能移动到next()元素或remove()一个元素。
但是 Collection 可以add() ，迭代， remove()或clear()集合的元素。 - Iterator 提供了比 Collections 更好的速度，因为 Iterator 接口的操作数量有限。
- Java.sql.SQLException 扩展了 Iterable 。因此，它允许调用者安全地遍历 SQLException 的原因。
在这种情况下，使用集合会很昂贵，因为在 n 个异常链中，在 SQLException 接口中使用集合可能需要构造 O(n^2) 个元素。
然而，使用 Iterable 提供了对异常链的 O(n) 访问。