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
private Address address;
person表

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@Overridepublic 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;}}