HashMap-2023-1-2

package Collection;

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;

public class MapTest {

    public Map<String,Student> students;

    public MapTest() {
        this.students = new HashMap<String,Student>();
    }

    //测试添加
    public void testPut(){
        //创建一个scanner类，用于录入学生ID和姓名
        Scanner console = new Scanner(System.in);
        int i=0;
        while (i<3){
            System.out.println("请输入学生ID:");
            String ID = console.next();
            //判定是否被占用
            Student st = students.get(ID);
            if (st==null){
                //提示输入学生姓名
                System.out.println("请输入学生姓名：");
                String name = console.next();
                //创建新的学生对象
                Student newstudent = new Student(ID, name);
                //通过调用PUT方法，添加ID-学生映射
                students.put(ID,newstudent);
                System.out.println("成功添加学生："+students.get(ID).name);
                i++;}
            else {
                System.out.println("该ID已被占用");
                continue;
            }
            }
        }

        public void testKeySet(){
            // 通过KEYSET方法，返回Map中的所有“键”的SET集合
            Set<String> keySet = students.keySet();
            //取得students容量大小
            System.out.println("总共有："+students.size()+"个学生");
            //通过遍历keyset，取得每一个键，再调用get方法取得每个键对应的value
            for (String stuId:keySet) {
                Student st = students.get(stuId);
                if (st!=null)
                    System.out.println("学生："+st.name);
            }
        }

        //测试删除MAP中的映射
    public void testRemove(){

        Scanner console = new Scanner(System.in);
        while (true){
            System.out.println("请输入要删除的学生ID:");
            String ID = console.next();
            //把ID的东西给学生对象,判断是否有对应学生对象
            Student st = students.get(ID);
            if (st==null){
                System.out.println("该ID不存在");
                continue;
            }
            students.remove(ID);
            System.out.println("成功删除学生"+st.id+st.name);
            break;
        }
    }

    //通过ENTRYSET来遍历
    public void testEntrySet(){
        Set<Map.Entry<String,Student>> entrySet = students.entrySet();
        for (Map.Entry<String,Student>entry:entrySet){
            System.out.println("取得键："+entry.getKey());
            System.out.println("对应的值为："+entry.getValue().id+entry.getValue().name);
        }
    }

    /**
     利用put方法修改MAP中的已有映射
     */
     public void testModify(){
         //提示输入要修改的学生
         System.out.println("请输入要修改的学生ID:");
         //录入
         Scanner console = new Scanner(System.in);
         while (true){
             String stuID = console.next();
             Student student = students.get(stuID);
             if (student==null){
                 System.out.println("该ID不存在，请重新输入");
                 continue;
             }
             System.out.println("当前该学生ID，所对应的学生为："+student.name);
             //输入新的姓名
             System.out.println("请输入新的学生姓名：");
             String name = console.next();
             Student newStudent = new Student(stuID,name);
             students.put(stuID,newStudent);
             System.out.println("修改成功！");
             break;
         }


     }

    public static void main(String[] args) {
        MapTest mt = new MapTest();
        mt.testPut();
        mt.testKeySet();
        //mt.testRemove();
        //mt.testEntrySet();
        mt.testModify();
        mt.testEntrySet();
    }

}