@Id字段映射和方法映射

http://www.blogjava.net/hadeslee/archive/2007/09/11/144275.html

EJB初学日记(5)

以前看到一本书上写的,有关定义实体BEAN的一些细节,直到今天才知道其中的差别
代码1:

/*
* Test.java
*
* Created on 2006年12月15日, 上午12:06
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/
package com.hadeslee.entity;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
/**
* Entity class Test
*
* @author lbf
*/
@Entity
public class Test implements Serializable {
private Long id;
private String name,sex,age;
private int idCard;
/** Creates a new instance of Test */
public Test() {
}
/**
* Gets the id of this Test.
* @return the id
*/
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
public Long getId() {
return this.id;
}
/**
* Sets the id of this Test to the specified value.
* @param id the new id
*/
public void setId(Long id) {
this.id = id;
}
public void setNameID(int ids){
this.idCard=ids;
}
public int getNameID(){
return idCard;
}
/**
* Returns a hash code value for the object.  This implementation computes
* a hash code value based on the id fields in this object.
* @return a hash code value for this object.
*/
@Override
public int hashCode() {
int hash = 0;
hash += (this.id != null ? this.id.hashCode() : 0);
return hash;
}
/**
* Determines whether another object is equal to this Test.  The result is
* true if and only if the argument is not null and is a Test object that
* has the same id field values as this object.
* @param object the reference object with which to compare
* @return true if this object is the same as the argument;
* false otherwise.
*/
@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Test)) {
return false;
}
Test other = (Test)object;
if (this.id != other.id && (this.id == null || !this.id.equals(other.id))) return false;
return true;
}
/**
* Returns a string representation of the object.  This implementation constructs
* that representation based on the id fields.
* @return a string representation of the object.
*/
@Override
public String toString() {
return "com.hadeslee.entity.Test[id=" + id + "]";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
}

代码2:

/*
* Test.java
*
* Created on 2006年12月15日, 上午12:06
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/
package com.hadeslee.entity;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
/**
* Entity class Test
*
* @author lbf
*/
@Entity
public class Test implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name,sex,age;
private int idCard;
/** Creates a new instance of Test */
public Test() {
}
/**
* Gets the id of this Test.
* @return the id
*/
public Long getId() {
return this.id;
}
/**
* Sets the id of this Test to the specified value.
* @param id the new id
*/
public void setId(Long id) {
this.id = id;
}
public void setNameID(int ids){
this.idCard=ids;
}
public int getNameID(){
return idCard;
}
/**
* Returns a hash code value for the object.  This implementation computes
* a hash code value based on the id fields in this object.
* @return a hash code value for this object.
*/
@Override
public int hashCode() {
int hash = 0;
hash += (this.id != null ? this.id.hashCode() : 0);
return hash;
}
/**
* Determines whether another object is equal to this Test.  The result is
* true if and only if the argument is not null and is a Test object that
* has the same id field values as this object.
* @param object the reference object with which to compare
* @return true if this object is the same as the argument;
* false otherwise.
*/
@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Test)) {
return false;
}
Test other = (Test)object;
if (this.id != other.id && (this.id == null || !this.id.equals(other.id))) return false;
return true;
}
/**
* Returns a string representation of the object.  This implementation constructs
* that representation based on the id fields.
* @return a string representation of the object.
*/
@Override
public String toString() {
return "com.hadeslee.entity.Test[id=" + id + "]";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public String getAge() {
return age;
}
public void setAge(String age) {
this.age = age;
}
}

代码1和代码2唯一的差别就是@Id的注释地方不同了

同样是注释主键,当在直接用在变量上注释时,如果其它的成员变量没有指定名字,则数据库生成的表的各列名字将以定义的成员变量的变量名为准

当用在getter方法注释时,则数据库生成的表的各列名字将取getXXXX的XXXX名字,将不再取定义的成员变量名

像上面的例子中,代码1会有IdCard这一列,则代码2取而代之的将是NameID这一列.这看上去是一个小小的差别,但是了解了终究是好事.呵呵.终于懂清楚在get上注释和直接在成员变量上注释的差别了,一般来说是不会有什么差别的,一般标准 的JAVABEAN都是成员变量名和getter,setter签名一样的.