Collection collection
The concept of the collection:
It is used to store a set of reference data type container, when adding the basic data types , the system automatically packing wrapper class objects to add to the collection
Collection are two major categories:
Collection Collection: accessing data is a single access
Map collections: a press < key, value> pairs form of access to data, such as: < "lisi", 18> , < "zhangsan", 20>
Collection of a set of common methods:
When you define Collection object, as Collection is an interface, you need to assign implementation class objects
Usually only one set of a type of data storage, can be generic to constrain the set of element types in
add () method: add elements to the collection
isEmpty () : whether the specified set is empty
size () : the number of elements in the set is determined
contains (element name) : determining whether the element is present
remove (element name) : remove the first matching element.
toArray (array name) : the collection into an array
