Java数据结构－Collection（一）
Java中集合的框架图
Collection is the root of the collection hierarchy. It defines operations on data collections and the behavior that they will have in all implementations of Collections. All direct or indirect implementations of Collection should implement at least two constructors. One with no parameters which creates an empty collection and one with a parameter of type Collection. This second constructor can be used to create a collection of different type as the initial collection but with the same elements. Implementations of Collection cannot be forced to implement these two constructors but at least all implementations under java.util do. Methods that change the content of a collection throw an UnsupportedOperationException if the underlying collection does not support that operation, though it's not mandatory to throw such an Exception in cases where the requested operation would not change the collection. In these cases it's up to the implementation whether it throws an UnsupportedOperationException or not. Methods marked with (optional) can throw an UnsupportedOperationException if the underlying collection doesn't support that method.
collection 是collection体系中的根接口，它定义了所有实现该接口的类的数据集合的操作和行为。所有直接或者间接实现该接口的类应该实现至少两个构造函数。一个无参的函数用来创建一个空的collection，一个函数接收一个类型参数。第二个函数可以创建一个collection用来存储与参数声明的类型一致的数据。collection的实现类不强制要求必须实现这两个构造函数，但是java.util包里的实现类都这样做了。改变collection内容的操作可能导致UnsupportedOperationException异常，如果collection底层不支持这种操作的话。在请求的操作不会如预期一样改变collection的时候，它不会强制是否抛出一个异常。在这些情况下，由实现类决定是否抛出UnsupportedOperationException异常。带（optional）标记的函数是可选择实现的方法，可能由于未实现而导致UnsupportedOperationException异常。
collection接口继承iterable接口。iterable接口实现类可以进行增强for循环。
publicinterface Iterable
/**
* Returns an {@link Iterator} for the elements in this object.
*
* @return An {@code Iterator} instance.
*/
Iterator
}
collection的子类：
collection方法概述：
public abstract boolean add (E object)
Attempts to add object to the contents of this Collection (optional). After this method finishes successfully it is guaranteed that the object is contained in the collection. If the collection was modified it returns true, false if no changes were made. An implementation of Collection may narrow the set of accepted objects, but it has to specify this in the documentation. If the object to be added does not meet this restriction, then an IllegalArgumentException is thrown. If a collection does not yet contain an object that is to be added and adding the object fails, this method must throw an appropriate unchecked Exception. Returning false is not permitted in this case because it would violate the postcondition that the element will be part of the collection after this method finishes.
该方法尝试将对象加入collection中。该方法成功调用结束后将会保证被添加的对象包含在collection中。如果collection被修改了，该方法将会反悔true，如果collection没有变化，将会返回false。collection的实现类可能会限制可以接收的对象的范围，但是必须在文档中申明。如果被添加的对象不符合限制要求的话，就会抛出IllegalArgumentException异常。如果一个collection没有包含要被添加的对象，而且添加该对象失败了，那么必须抛出 appropriate unchecked Exception异常。这种情况下不被允许返回false，因为它可能会破坏后来的结果－方法结束后该对象成为了collection的一部分。
Parameters
| object | the object to add. |
|---|
Returns
trueif thisCollectionis modified,falseotherwise.
Throws
| UnsupportedOperationException | if adding to this Collection is not supported. |
|---|---|
| ClassCastException | if the class of the object is inappropriate for this collection. |
| IllegalArgumentException | if the object cannot be added to this Collection. |
| NullPointerException | if null elements cannot be added to the Collection. |
public abstract boolean addAll (Collection collection)
Attempts to add all of the objects contained in Collection to the contents of this Collection (optional). If the passed Collection is changed during the process of adding elements to this Collection, the behavior is not defined.
该方法将尝试把另外一个collection中包含的所有对象添加到此collection中。如果在此过程中，被添加的collection发生了改变，这种情形没有做出定义。（保证在此过程中被添加的collection未被改变。）
Parameters
| collection | the Collection of objects. |
|---|
Returns
trueif thisCollectionis modified,falseotherwise.
Throws
| UnsupportedOperationException | if adding to this Collection is not supported. |
|---|---|
| ClassCastException | if the class of an object is inappropriate for this Collection. |
| IllegalArgumentException | if an object cannot be added to this Collection. |
| NullPointerException | if collection is null, or if it contains null elements and this Collection does not support such elements. |
public abstract void clear ()
Removes all elements from this Collection, leaving it empty (optional).
移除该collection中的所有元素，使其为空。
Throws
| UnsupportedOperationException | if removing from this Collection is not supported. |
|---|
See Also
isEmpty()size()
public abstract boolean contains (Object object)
Tests whether this Collection contains the specified object. Returns true if and only if at least one element elem in this Collection meets following requirement:(object==null ? elem==null : object.equals(elem)).
测试该collection是否包含特定的对象。当且仅当至少一个collection中的元素满足一下条件时（如果特定对象为null时，collection中有null元素，特定对象不为空时，该对象通过equals方法与元素比较后返回true）返回true。
Parameters
| object | the object to search for. |
|---|
Returns
trueif object is an element of thisCollection,falseotherwise.
Throws
| ClassCastException | if the object to look for isn't of the correct type. |
|---|---|
| NullPointerException | if the object to look for is null and this Collection doesn't support null elements. |
public abstract boolean containsAll (Collection collection)
Tests whether this Collection contains all objects contained in the specified Collection. If an element elem is contained several times in the specified Collection, the method returns true even if elem is contained only once in this Collection.
测试该collection是否包含特定collection中的所有对象，即使一个元素在特定的collection中出现多次，而此collection仅包含该元素一次也会返回true。
Parameters
| collection | the collection of objects. |
|---|
Returns
trueif all objects in the specifiedCollectionare elements of thisCollection,falseotherwise.
Throws
| ClassCastException | if one or more elements of collection isn't of the correct type. |
|---|---|
| NullPointerException | if collection contains at least one null element and this Collection doesn't support null elements. |
| NullPointerException | if collection is null. |
public abstract boolean equals (Object object)
Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
| object | the object to compare with this object. |
|---|
Returns
trueif the object is the same as this object andfalseif it is different from this object.
See Also
hashCode()
public abstract int hashCode ()
Returns an integer hash code for the receiver. Objects which are equal return the same value for this method.
Returns
- the receiver's hash.
See Also
equals(Object)
public abstract boolean isEmpty ()
Returns if this Collection contains no elements.
如果该collection没有元素，则返回true，否则返回false。
Returns
trueif thisCollectionhas no elements,falseotherwise.
See Also
size()
public abstract Iterator iterator ()
Returns an instance of Iterator that may be used to access the objects contained by this Collection. The order in which the elements are returned by the iterator is not defined. Only if the instance of the Collection has a defined order the elements are returned in that order.
该方法返回一个iterator实例对象，用来访问该collection中包含的对象。此iterator返回的顺序是无序的，只有当collection中已经定义了元素的返回顺序时，iterator才会按此顺序返回元素。
iterator对象来自于collection接口继承的iterable接口。
Returns
- an iterator for accessing the
Collectioncontents.
public abstract boolean remove (Object object)
Removes one instance of the specified object from this Collection if one is contained (optional). The element elem that is removed complies with (object==null ? elem==null : object.equals(elem).
如果该collection中包含需要移除的对象，那么将移除该对象的一个实例（可能包含该对象的多个实例，将移除一个）。
Parameters
| object | the object to remove. |
|---|
Returns
trueif thisCollectionis modified,falseotherwise.
Throws
| UnsupportedOperationException | if removing from this Collection is not supported. |
|---|---|
| ClassCastException | if the object passed is not of the correct type. |
| NullPointerException | if object is null and this Collection doesn't support null elements. |
public abstract boolean removeAll (Collection collection)
Removes all occurrences in this Collection of each object in the specified Collection (optional). After this method returns none of the elements in the passedCollection can be found in this Collection anymore.
移除特定collection中的所有对象在此collection中的存在。调用此方法后，特定collection中的元素不会在此collection中包含了。
Parameters
| collection | the collection of objects to remove. |
|---|
Returns
trueif thisCollectionis modified,falseotherwise.
Throws
| UnsupportedOperationException | if removing from this Collection is not supported. |
|---|---|
| ClassCastException | if one or more elements of collection isn't of the correct type. |
| NullPointerException | if collection contains at least one null element and this Collection doesn't support null elements. |
| NullPointerException | if collection is null. |
public abstract boolean retainAll (Collection collection)
Removes all objects from this Collection that are not also found in the Collection passed (optional). After this method returns this Collection will only contain elements that also can be found in the Collection passed to this method.
移除该collection中所有给定collection中未包含的对象。调用此方法后，此collection中将只包含在给定collection中也存的的元素。
Parameters
| collection | the collection of objects to retain. |
|---|
Returns
trueif thisCollectionis modified,falseotherwise.
Throws
| UnsupportedOperationException | if removing from this Collection is not supported. |
|---|---|
| ClassCastException | if one or more elements of collection isn't of the correct type. |
| NullPointerException | if collection contains at least one null element and this Collection doesn't support null elements. |
| NullPointerException | if collection is null. |
public abstract int size ()
Returns a count of how many objects this Collection contains.
返回该collection中包含的对象的数量。如果此数量超过了Integer的最大值，将会返回Integer的最大值。
Returns
- how many objects this
Collectioncontains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in thisCollection.
public abstract T[] toArray (T[] array)
Returns an array containing all elements contained in this Collection. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this Collection, the array element following the Collection elements is set to null. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. toArray(new Object[0]) behaves exactly the same way as toArray() does.
该方法将会返回一个包含此collection中所有元素的数组。如果给定的数组足以装下这些元素，就会使用给定的数组，否则将会创建一个新的同类型的数组。如果使用给定的数组且数组足以装下此collection的元素，那么数组中除了collection中的元素，后面的元素将会被设置为null。如果collection的实现类是有序的，那么数组中将会按此顺序存储元素。toArrary(new object[0])和toArray()是一样的。此方法不会对该collection造成影响。
Parameters
| array | the array. |
|---|
Returns
- an array of the elements from this
Collection.
Throws
| ArrayStoreException | if the type of an element in this Collection cannot be stored in the type of the specified array. |
|---|
public abstract Object[] toArray ()
Returns a new array containing all elements contained in this Collection. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. The array returned does not reflect any changes of the Collection. A new array is created even if the underlying data structure is already an array.
Returns
- an array of the elements from this
Collection.