Javase 13th Day 20160819

(2), Java.util.HashSet class: The elements in the collection are sorted according to the hash value. When you create a collection, you can specify the length of the collection, and by default increase the length of the collection by 75% when the length is insufficient.

4. List Collection

(1) , ArrayList : Linear data structures, which are efficient when querying elements based on location, and inefficient when adding and deleting elements. You can specify the length of the collection when you create the collection .

(2) , LinkedList : Linked list data structure, high efficiency when adding and deleting elements, low efficiency when querying elements based on location. the length of the collection cannot be specified when the collection is created .

(3) , Vector : With ArrayList the same functionality. Vectors are thread-safe and ArrayList are thread insecure.

5.Map Collection

(1) , Hashtable : Thread-safe. Null is not allowed as a key or value.

(2) , HashMap : Thread is not secure. Null is allowed as a key or value.

Seven, generics: JDK1.5 began to appear.

1. Late-bound data type.

2. Generics must be a subclass of object or object.

3. If you do not specify a generic type, the default is type object.

4. Generic extends class: Adding a condition to a generic type

Javase 13th Day 20160819