ArrayList collection

The reason why sets appear
Arrays store data in fixed storage. When the number of data to be stored is uncertain, the array is not satisfied, and sets appear
Sets The number of stored data can change as the amount of data changes, without causing cross-border or a large amount of space waste
The number of stored data is variable

ArrayList:
Under the java.util package
The bottom layer maintains an array
The thread is not synchronized (fast processing speed)

Format of creating ArrayList object:
ArrayList< ;E> Collection name = new ArrayList();
: Generic, represents the data type to be stored in the collection. Change E to the type you want to store. If you want to store For String type data, change E to String

Note: Collections can only store reference type data


Basic data types Corresponding reference data type representation
byte Byte
short Short
int Integer
long Long
float Float
double Double
char Character
boolean Boolean

Common functions of ArrayList
Add
public boolean add(E e)
public void add(int index,E element) // Add at the specified index position Element

Get the element
public E get(int index)//Get the element based on the index value

Get the number of elements
public int size() //Get Number of elements

Delete elements
public boolean remove(Object o) //Delete elements directly
public E remove(int index) //Delete elements based on index and return the deleted elements

Modify elements
public E set(int index,E element)//Use element to replace the element at the specified index and return the replaced element

Student Management System Exercise
Student information includes: student ID, name, age, hometown
Print welcome statement
Print corresponding functions, and receive user input

1. View student information
If the system If there is no student information, the corresponding prompt will be given
If there is student information in the system, the student information will be printed in the specified format
2. Add student information
Enter the student's information from the keyboard to form an object and add it to the collection
Remove duplicates based on student numbers. Only non-duplicated student numbers can be added to the collection

3. Modify student information
Find the student based on the student number and modify it
If there is no student number, give Prompt the corresponding prompt
If the student number is found, continue to collect new information and use the new information to modify the original elements
4. Delete student information
Delete the student based on the student number
If no student number is specified, give Out the specified prompt
If there is a student number, delete the specified element
5. Exit the student information management system
Prompt to exit
and end the program
Code demonstration

  1 public static void main(String[] args) {  
  2         // 初始化数据  
  3         // 创建一个集合容器 可以存储学生的信息  
  4         ArrayList<student> list = new ArrayList<student>();  
  5         // =========================测试数据================================  
  6 //        Student s1 = new Student("9001", "阿拉甲", "18", "迪拜");  
  7 //        Student s2 = new Student("9002", "阿拉yi", "18", "迪拜");  
  8 //        Student s3 = new Student("9003", "阿拉饼", "18", "迪拜");  
  9 //        list.add(s1); 
  10 //        list.add(s2); 
  11 //        list.add(s3); 
  12 //        System.out.println("初始化完毕"); 
  13         // =========================测试数据================================ 
  14  
  15         System.out.println("-------------------欢迎使用学生管理系统------------------------"); 
  16  
  17         // 死循环
  18         while (true) { 
  19             // 展示功能菜单 
  20             System.out.println("================================="); 
  21             System.out.println("1.查看学生信息"); 
  22             System.out.println("2.添加学生信息"); 
  23             System.out.println("3.修改学生信息"); 
  24             System.out.println("4.删除学生信息"); 
  25             System.out.println("5.退出学生信息管理系统");
   26             System.out.println("请输入对应功能的序号"); 
   27             System.out.println("================================="); 
   28             // 接收用户的输入 
   29             Scanner sc = new Scanner(System.in); 
   30             int user = sc.nextInt(); 
   31             // 根据用户的输入进行功调用 
   32             switch (user) { 
   33             case 1: 
   34                 show(list); 
   35                 break; 
   36             case 2: 
   37                 add(list); 
   38                 break; 
   39             case 3: 
   40                 upd(list); 
   41                 break; 
   42             case 4: 
   43                 del(list); 
   44                 break; 
   45             case 5: 
   46                 System.out.println("感谢使用管理系统 欢迎下次再来哦  "); 
   47                 // 终止虚拟机 
   48                 System.exit(0); 
   49                 // return; 
   50                 break; 
   51  
   52             default: 
   53                 System.out.println("对不起 没有这个功能 ,请控制你自己 "); 
   54                 break; 
   55             } 
   56         } 
   57     } 
   58  
   59     // 功能方法s 
   60     public static void del(ArrayList<student> list) { 
   61         // 1.提示输入学号
   62         Scanner sc = new Scanner(System.in); 
   63         System.out.println("请输入学号"); 
   64         String id = sc.next(); 
   65 
   66         // 2.查找
   67         // 定义标记 
   68         int index = -1; 
   69         // 遍历比较 并修改 
   70         for (int i = 0; i  list) { 
   92         // 1.提示输入学号 
   93         Scanner sc = new Scanner(System.in); 
   94         System.out.println("请输入学号"); 
   95         String id = sc.next(); 
   96  
   97         // 2.查找 
   98         // 定义标记 
   99         int index = -1;
   100         // 遍历并比较
   101         for (int i = 0; i  list) {
   134         // 1.提示输入学号
   135         Scanner sc = new Scanner(System.in);
   136         System.out.println("请输入学号");
   137         String id = sc.next();
   138         // 2.根据学号去重
   139 
   140         // 使用用户输入的学号去集合中查找, 如果找到与用户输入的学号一样的学号表示有重复,此时要继续提示输入学号,并继续去重
   141         // 直到用户输入的学号与集合中元素的学号不一致的时候再收集其他的信息
   142         while (true) {
   143             // 定义一个标记 给一个默认值
   144             int index = -1;
   145             // 遍历集合获取元素的学号与用户输入的学号进行比较
   146             for (int i = 0; i  list) {
   182         // 1.判断集合是否有元素
   183         if (list.size() == 0) {
   184             // 如果没有给出特定的提示
   185             System.out.println("系统中没有学生的信息,请选择添加功能");
   186         } else {
   187             // 如果有就按照指定格式遍历
   188             System.out.println("================学生信息如下====================");
   189             System.out.println("学号\t\t姓名\t\t年龄\t\t家乡");
   190             // 遍历集合获取学生信息
   191             for (int i = 0; i </student></student></student>

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