实体类之间实现一对一或一对多的关联

public class studentEntity {

    private int StudentNo;
    private String LoginPwd;
    private String StudentName;
    private int Sex;
    private int GradeId;
    private String Phone;
    private String Address;
    private Date BornDate;
    private String Email;
    private String IdentityCard;
　　//关联gradeEntity表与studentEntity表---  一对一
    private gradeEntity grade;

public class gradeEntity {
    
    private int GradeID;
    private String GradeName;
　　//关联gradeEntity表与studentEntity表---  一对多
    private List<studentEntity> listStudent;

/**
     * 查所有学生记录并保存到实体类中
     * @throws SQLException 
     */
    @Test
    public void show() throws SQLException{
        String sql="SELECT *FROM student INNER JOIN grade ON student.GradeId=grade.GradeID";
        ResultSet rs=getAll(sql);
        List<studentEntity> list=new ArrayList<studentEntity>();
        if (rs!=null) {
            while (rs.next()) {
                gradeEntity gs=new gradeEntity();
                studentEntity ss=new studentEntity();
                ss.setStudentNo(rs.getInt("studentNo"));
                ss.setStudentName(rs.getString("studentName"));
                gs.setGradeName(rs.getString("gradeName"));
                ss.setGrade(gs);
                list.add(ss);
            }
        }
        for (studentEntity se : list) {
            System.out.println("学生姓名："+se.getStudentName()+"年纪姓名："+se.getGrade().getGradeName());
        }
    }

/**
     * 查S1下的所有学生记录并保存到实体类中
     * @throws SQLException 
     */
    public void shows() throws SQLException{
        String sql="SELECT *FROM student INNER JOIN grade ON student.GradeId=grade.GradeID where grade.GradeName='S1'";
        ResultSet rs=getAll(sql);
        List<studentEntity> list=new ArrayList<studentEntity>();
        gradeEntity gs=new gradeEntity();
        if (rs!=null) {
            while (rs.next()) {
                studentEntity ss=new studentEntity();
                ss.setStudentNo(rs.getInt("studentNo"));
                ss.setStudentName(rs.getString("studentName"));
                gs.setGradeName(rs.getString("gradeName"));
                ss.setGrade(gs);
                list.add(ss);
            }
        }
        gs.setListStudent(list);
        for (studentEntity se : list) {
            System.out.println("学生姓名："+se.getStudentName()+"年纪姓名："+se.getGrade().getGradeName());
        }
    }