JAVA集合框架Map特性及实例解析

package com.collection;

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

public class MapTest {

  public HashMap<String,Student> students = new HashMap<String,Student>();

  /*
  * 新建学生到Map中
  * */
  public void addStudent(){
    //先添加三个学生
    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();
      Student s = students.get(id);
      if(s == null){
        System.out.println("请输入学生姓名：");
        String name = console.next();
        Student student = new Student(Integer.parseInt(id),name);
        students.put(id,student);
        System.out.println("添加了学生："+student.id+"-"+student.name);
        i++;
      }else{
        System.out.println("该ID已经被占用");
        continue;
      }
    }
  }

  /*
  * 试用HashMap的keySet方法
  *
  * 顺便遍历Students
  * */
  public void forEachStudents(){
    Set<String> ks = students.keySet();
    System.out.println("共有学生数量"+students.size()+"个，具体如下：");
    for(String key: ks){
      Student student = students.get(key);
      if( student != null){
        System.out.println("学生ID："+student.id+"-学生姓名："+student.name);
      }
    }
  }

  public static void main(String[] args){
    MapTest mt = new MapTest();
    mt.addStudent();
    mt.forEachStudents();
  }
}

package com.collection;

import java.util.HashSet;
import java.util.Set;

public class Student {
  public int id;
  public String name;

  //set中添加某个对象无论添加多少次，最终只会保留一个该对象（的引用），并且，保留的是第一次添加的那个

  public Set<Course> course = new HashSet<Course>();

  public Student(int id, String name){
    this.id = id;
    this.name = name;
  }

}