Java 程式設計基礎班 (7) 莊坤達台大電信所網路資料庫研究室. Java I/O. Class 7 1. Class 7 2

Transcription

1 Java 程式設計基礎班 (7) 莊坤達台大電信所網路資料庫研究室 Class 7 1 回顧 Java I/O Class 7 2

2 Java Data Structure 動態資料結構 Grow and shrink at execution time Several types Linked lists Stacks Queues Binary trees Class 7 3 Self-Referential Classes Self-referential class Contains instance variable referring to object of same class class Node { private int data; private Node nextnode; // reference to next linked node } Member nextnode is a link nextnode 連結到另一個 Node object Class 7 4

3 Self-Referential Classes Class 7 5 動態記憶體配置 Dynamic memory allocation 在執行期要求更多的記憶體來儲存新的物件 JVM 的記憶體是一個可改變大小的 heap structure 可以用 -Xms 和 -Xmx 來跟 JVM 要求起始配置的 heap 大小, e.g., java Xmx1600mb myclass WindowsXP+JRE1.4.0 最大可以到 16xxmb 左右 Class 7 6

4 Linked Lists Linked list Linear collection of self-referential classes (nodes) Connected by reference links Nodes 可以 insert 或 delete, 即使它不在 list 的開頭或結尾 Last node is set to null to mark end of list Class 7 7 Linked Lists firstnode lastnode... H D Q Class 7 8

5 (a) firstnode 20.4 Linked Lists (cont.) 7 11 new Listnode 12 (b) firstnode 7 11 new Listnode 12 Graphical representation of operation insertatfront. Class 7 9 (a) firstnode lastnode new Listnode 20.4 Linked Lists (cont.) (b) firstnode lastnode new Listnode Graphical representation of operation insertatback. Class 7 10

6 (a) firstnode lastnode 20.4 Linked Lists (cont.) (b) firstnode lastnode removeitem Graphical representation of operation removefromfront. Class 7 11 (a) firstnode lastnode 20.4 Linked Lists (cont.) (b) firstnode current lastnode removeitem Graphical representation of operation removefromback. Class 7 12

7 Queues Queue 先進先出 可以想像一個 supermarket 的購物 checkout List Nodes inserted only at tail (back) Method enqueue Nodes removed only from head (front) Method dequeue Class 7 13 Stacks 先進後出 E.g., 停車 Class 7 14

8 Trees Tree Non-linear, two-dimensional data structure ( 有別於 linked lists, stacks and queues) 每一個 Node 有兩個 ( 或以上 ) 的 Links Root node is the first node Each link refers to a child Left child is the first node in left subtree Right child is the first node in right subtree Children of a specific node are siblings Nodes with no children are leaf nodes Class 7 15 Trees Binary search tree Special ordering of nodes Values in left subtrees are less than values in right subtrees Inorder traversal Traverse left subtree, obtain node value, traverse right subtree Preorder traversal Obtain node value, traverse left subtree, traverse right subtree Postorder traversal Traverse left subtree, traverse right subtree, obtain node value Class 7 16

9 20.7 Trees (cont.) B A D C Binary tree graphical representation. Class 7 17 Trees 見 v/idsv.html Class 7 18

10 20.7 Trees 47 (cont.) Binary search tree containing 12 values. InOrder 7,11,17,25,31,43,44,47 PreOrder 47,25,11,7,17,43,31,44 PostOrder 7,17,11,31,44,43,25 Class 7 19 Java collections framework Java collections framework Provides reusable componentry Common data structures Example of code reuse Class 7 20

11 Collections Overview Collection Data structure (object) that can hold references to other objects Collections framework Interfaces declare operations for various collection types Belong to package java.util Collection Set List Class 7 21 Map Collections Overview Class 7 22

12 Lists List Ordered Collection that can contain duplicate elements Sometimes called a sequence Implemented via interface List ArrayList LinkedList Vector Class 7 23 Class 7 24

13 Algorithms 在 Collections 物件中提供了一些對 collection 的基本運作 algorithms Implemented as static methods List algorithms Sort,binarySearch,reverse,shuffle,fill,copy Collection algorithms Min,max 在 Arrays 物件中提供了一些對 array 運作的函式 Class 7 25 Sets Set Collection that contains unique elements HashSet Stores elements in hash table TreeSet Stores elements in tree Class 7 26

14 Maps Map Associates keys to values Cannot contain duplicate keys Called one-to-one mapping 要有 hashcode() 才行 Class 7 27 Unmodifiable Collection Unmodifiable Collection 將一個 collection 轉成不可被修改的 collection Throw UnsorrtedOperationException 假設要 modifiy 它的話 Class 7 28