当写表和实体类之间映射的时候，一旦出现外键，要通过外键找到另外一个类，一旦出现外键必须写成类型

public class Person {    private String pid;    private String pname;    private int age;    private Address address;    public Address getAddress() {        return address;    }    public void setAddress(Address address) {        this.address = address;    }    public String getPid() {        return pid;    }    public void setPid(String pid) {        this.pid = pid;    }    public String getPname() {        return pname;    }    public void setPname(String pname) {        this.pname = pname;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    //覆盖原来的toString方法    @Override    public String toString() {        return "Person [pid=" + pid + ",pname=" + pname + ",age=" + age +"]";    }}

public class Address {    private String aid; //主键    private String province; //省    private String city; //市    private String district; //区    private String street; //街道    public String getAid() {        return aid;    }    public void setAid(String aid) {        this.aid = aid;    }    public String getProvince() {        return province;    }    public void setProvince(String province) {        this.province = province;    }    public String getCity() {        return city;    }    public void setCity(String city) {        this.city = city;    }    public String getDistrict() {        return district;    }    public void setDistrict(String district) {        this.district = district;    }    public String getStreet() {        return street;    }    public void setStreet(String street) {        this.street = street;    }}