Java-Map测试-学生选课

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package collection;import java.util.*;import java.util.Map.Entry;public class MapTest {    //承装学生类型对象    public Map<String,Student> students;    private Scanner console;    //在构造器中初始化students属性    public MapTest()    {        this.students = new HashMap<String,Student>();        console = new Scanner(System.in);    }    //测试添加     public void testPut()    {        //输入学生id，判断是否被占用        Scanner console = new Scanner(System.in);        int i=0;        while(i < 3)        {            System.out.println("输入学生ID：");            String ID = console.next();            Student st = students.get(ID);            if(st == null)            {                //若未被占用 输入姓名创建新学生对象并添加到students中                System.out.println("请输入学生姓名：");                String name = console.next();                Student newStudent = new Student(ID,name);                students.put(ID, newStudent);                System.out.println("成功添加学生："+students.get(ID).name);                i++;            }            else            {                System.out.println("该学生ID已被占用。");                continue;            }        }    }    //测试Map的keySet方法    public void testKeySet()    {        //通过keySet方法返回所有键的Set集合        Set<String> keySet = students.keySet();        //取得students容量        System.out.println("总共有："+students.size()+"个学生");        //遍历keySet取得每一个键 通过get方法得到value        //Map中的元素也是无序的        for(String stuId:keySet)        {            Student st = students.get(stuId);            if(st!=null)            {                System.out.println("学生"+ st.name);            }        }    }    //测试删除Map中已有映射    public void testRemove()    {        Scanner console = new Scanner(System.in);        while(true)        {            //提示输入待删除学生ID            System.out.println("输入要删除的学生ID：");            String ID = console.next();             //判断此ID是否有对应学生            Student st = students.get(ID);            if(st == null)            {                System.out.println("输入的ID不存在。");                continue;            }            else            {                students.remove(ID);                System.out.println("成功删除学生："+st.name);                break;            }        }    }    //通过entreSet遍历Map    public void testEntrySet()    {        //返回所有键值对 用entry泛型的Set来接收        Set<Entry<String,Student>> entrySet = students.entrySet();        for(Entry<String,Student> entry:entrySet)        {            System.out.println("ID："+entry.getKey());            System.out.println("姓名："+entry.getValue().name);        }    }    //put方法修改Map中已有映射    public void testModify()    {        //提示输入要修改学生ID        System.out.println("输入要修改的学生ID：");        Scanner console = new Scanner(System.in);        while(true)        {            String stuID = console.next();            //在students中查找ID对应的学生对象            Student student = students.get(stuID);            if(student == null)            {                System.out.println("该ID不存在，请重新输入。");                continue;            }            else            {                //提示当前对应学生姓名                System.out.println("当前ID所对应学生姓名为："+student.name);                //提示输入新的学生姓名                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;            }        }    }    //测试Map中是否包含某key值或value值    //判断学生ID、姓名是否被包含    public void testContainsKeyOrValue()    {        //查询学生ID是否存在        //在Map中用containsKey()方法来判断是否包含某Key值        System.out.println("请输入要查询的学生ID：");        String id = console.next();         System.out.println("您输入的学生ID为："+id+"，在学生映射表中是否存在？ "+                students.containsKey(id));        if(students.containsKey(id))        {            System.out.println("对应的学生为："+students.get(id).name);        }        //查询学生姓名是否存在        //用containsValue()方法来判断包含某Value值        System.out.println("请输入要查询的学生姓名：");        String name = console.next();           //得重写学生类的equals和hashCode方法        if(students.containsValue(new Student(null,name)))        {            System.out.println("学生映射表中包含学生："+name);        }        else        {            System.out.println("不存在该学生。");        }    }    public static void main(String[] args) {        MapTest mt = new MapTest();        mt.testPut();        mt.testKeySet();        //mt.testRemove();        //mt.testEntrySet();        //mt.testModify();        //mt.testEntrySet();        mt.testContainsKeyOrValue();    }}

package collection;import java.util.*;//学生类public class Student implements Comparable<Student> {    public String id;    public String name;    public Set<Course> courses;    @Override    public int hashCode() {        final int prime = 31;        int result = 1;        result = prime * result + ((name == null) ? 0 : name.hashCode());        return result;    }    @Override    public boolean equals(Object obj) {        if (this == obj)            return true;        if (obj == null)            return false;        if (!(obj instanceof Student))            return false;        Student other = (Student) obj;        if (name == null) {            if (other.name != null)                return false;        } else if (!name.equals(other.name))            return false;        return true;    }    public Student(String id,String name)    {        this.id = id;        this.name = name;        this.courses = new HashSet<Course>();    }    //按学生ID排序    @Override    public int compareTo(Student o) {        // 相等返回0 this对象较大返回正值 反之返回负值        return this.id.compareTo(o.id);    }}

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