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作用:区分同一个类的不同对象是否是同一个对象。
应用:在Hibernate 定义 Model实体类的 联合主键的时候用到。
举例说明:
1.数据库中的表
teacher表,包括三个字段,id、name、level。其中id和name作为联合主键。
2.类
在类的角度,如果想定义一个联合主键,使用多个属性作为实体类的关键字,那么方式为定义一个单独的类,里面包含多个属性,并且将这个类包含在原有类中。
应用:在Hibernate 定义 Model实体类的 联合主键的时候用到。
举例说明:
1.数据库中的表
teacher表,包括三个字段,id、name、level。其中id和name作为联合主键。
2.类
在类的角度,如果想定义一个联合主键,使用多个属性作为实体类的关键字,那么方式为定义一个单独的类,里面包含多个属性,并且将这个类包含在原有类中。
public
class Teacher{
private TeacherKey tk;
private String level;
public void setTeacherKey(TeacherKey tk){
this.tk = tk;
}
public TeacherKey getTk(){
return tk;
}
public void setLevel(String level){
this.level = level;
}
public String getLevel(){
return this.level;
}
}
private TeacherKey tk;
private String level;
public void setTeacherKey(TeacherKey tk){
this.tk = tk;
}
public TeacherKey getTk(){
return tk;
}
public void setLevel(String level){
this.level = level;
}
public String getLevel(){
return this.level;
}
}
public
class TeacherKey{
private int id;
private String name;
public void setId( int id){
this.id = id;
}
public int getId(){
return this.id;
}
public void setName(String name){
this.name = name;
}
public String getName(){
return this.name;
}
public boolean equals(Object o){
if(o.instanceof TeacherKey){
Teacherkey tk = (TeacherKey)o;
if(this.id == tk.getId() && this.name.equals(tk.getName())){
return true;
}
}
return false;
}
public int hashCode(){
return this.name.hashCode();
}
}
private int id;
private String name;
public void setId( int id){
this.id = id;
}
public int getId(){
return this.id;
}
public void setName(String name){
this.name = name;
}
public String getName(){
return this.name;
}
public boolean equals(Object o){
if(o.instanceof TeacherKey){
Teacherkey tk = (TeacherKey)o;
if(this.id == tk.getId() && this.name.equals(tk.getName())){
return true;
}
}
return false;
}
public int hashCode(){
return this.name.hashCode();
}
}
3.项目中用到的代码示例:
package iq.model.user;
import java.io.Serializable;
public class User implements Serializable {
private String id;
private String name;
private String password;
private String email;
private String mobile;
private String desc;
private String type;
private String state;
private static final long serialVersionUID = 1L;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id == null ? null : id.trim();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name == null ? null : name.trim();
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password == null ? null : password.trim();
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email == null ? null : email.trim();
}
public String getMobile() {
return mobile;
}
public void setMobile(String mobile) {
this.mobile = mobile == null ? null : mobile.trim();
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc == null ? null : desc.trim();
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type == null ? null : type.trim();
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state == null ? null : state.trim();
}
@Override
public boolean equals(Object that) {
if (this == that) {
return true;
}
if (that == null) {
return false;
}
if (getClass() != that.getClass()) {
return false;
}
User other = (User) that;
return (this.getId() == null ? other.getId() == null : this.getId().equals(other.getId()))
&& (this.getName() == null ? other.getName() == null : this.getName().equals(other.getName()))
&& (this.getPassword() == null ? other.getPassword() == null : this.getPassword().equals(other.getPassword()))
&& (this.getEmail() == null ? other.getEmail() == null : this.getEmail().equals(other.getEmail()))
&& (this.getMobile() == null ? other.getMobile() == null : this.getMobile().equals(other.getMobile()))
&& (this.getDesc() == null ? other.getDesc() == null : this.getDesc().equals(other.getDesc()))
&& (this.getType() == null ? other.getType() == null : this.getType().equals(other.getType()))
&& (this.getState() == null ? other.getState() == null : this.getState().equals(other.getState()));
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((getId() == null) ? 0 : getId().hashCode());
result = prime * result + ((getName() == null) ? 0 : getName().hashCode());
result = prime * result + ((getPassword() == null) ? 0 : getPassword().hashCode());
result = prime * result + ((getEmail() == null) ? 0 : getEmail().hashCode());
result = prime * result + ((getMobile() == null) ? 0 : getMobile().hashCode());
result = prime * result + ((getDesc() == null) ? 0 : getDesc().hashCode());
result = prime * result + ((getType() == null) ? 0 : getType().hashCode());
result = prime * result + ((getState() == null) ? 0 : getState().hashCode());
return result;
}
}
import java.io.Serializable;
public class User implements Serializable {
private String id;
private String name;
private String password;
private String email;
private String mobile;
private String desc;
private String type;
private String state;
private static final long serialVersionUID = 1L;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id == null ? null : id.trim();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name == null ? null : name.trim();
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password == null ? null : password.trim();
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email == null ? null : email.trim();
}
public String getMobile() {
return mobile;
}
public void setMobile(String mobile) {
this.mobile = mobile == null ? null : mobile.trim();
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc == null ? null : desc.trim();
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type == null ? null : type.trim();
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state == null ? null : state.trim();
}
@Override
public boolean equals(Object that) {
if (this == that) {
return true;
}
if (that == null) {
return false;
}
if (getClass() != that.getClass()) {
return false;
}
User other = (User) that;
return (this.getId() == null ? other.getId() == null : this.getId().equals(other.getId()))
&& (this.getName() == null ? other.getName() == null : this.getName().equals(other.getName()))
&& (this.getPassword() == null ? other.getPassword() == null : this.getPassword().equals(other.getPassword()))
&& (this.getEmail() == null ? other.getEmail() == null : this.getEmail().equals(other.getEmail()))
&& (this.getMobile() == null ? other.getMobile() == null : this.getMobile().equals(other.getMobile()))
&& (this.getDesc() == null ? other.getDesc() == null : this.getDesc().equals(other.getDesc()))
&& (this.getType() == null ? other.getType() == null : this.getType().equals(other.getType()))
&& (this.getState() == null ? other.getState() == null : this.getState().equals(other.getState()));
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((getId() == null) ? 0 : getId().hashCode());
result = prime * result + ((getName() == null) ? 0 : getName().hashCode());
result = prime * result + ((getPassword() == null) ? 0 : getPassword().hashCode());
result = prime * result + ((getEmail() == null) ? 0 : getEmail().hashCode());
result = prime * result + ((getMobile() == null) ? 0 : getMobile().hashCode());
result = prime * result + ((getDesc() == null) ? 0 : getDesc().hashCode());
result = prime * result + ((getType() == null) ? 0 : getType().hashCode());
result = prime * result + ((getState() == null) ? 0 : getState().hashCode());
return result;
}
}