SA9 collections

 【定义】

 表示object的集合

generic class:可以用于多种object, 

 

 

抽象类的具体实现：

 【ArrayList】

动态添加，只能加Non-primitive type，要初始化长度。 

 

 

【compare】记忆方法：BT1 用this,T02 用object

comparable:比较natural order，comparator的compare可以比较2个物体，定义不同的order

public void sortAndPrint() {
Collections.sort(books); //natural order
printCollection();
Collections.sort(books, new AuthorComparer());
printCollection();
Collections.sort(books, new YearComparer());
printCollection();
}
//inner classes
public class AuthorComparer implements Comparator <Book> {
public int compare(Book b1, Book b2) {
return b1.author.compareTo(b2.author);
}}
public class YearComparer implements Comparator <Book>  {
public int compare(Book b1, Book b2) {
return (b1.year - b2.year); 
  }
}}

 【iterator】

【Arraylist】

只存了引用，元素的位置随意。

Java offers only doubly linked list data structure. If you needed a circular or a singly linked list in your program, 

Create my own custom-made linked list。只有双向链表。