hibernate 實現equals方法
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<span class="time">2018年05月29日 21:59:58</span>
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<div style="text-align:left;"><span style="color:rgb(51,51,51);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;font-size:14px;background-color:rgb(255,255,255);">對數據庫而言，其識別一條記錄的唯一性的方式是根據主鍵值，如果有兩條記錄，它們擁有同樣的主鍵值，則它們在數據庫中代表同一字段的記錄。</span></div><div style="text-align:left;"><span style="color:rgb(51,51,51);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;font-size:14px;background-color:rgb(255,255,255);">對</span><span style="background-color:rgb(255,255,255);font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;text-align:justify;">java而言要識別兩個對象是否爲同一對象有兩種方式 </span></div><p style="font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;background-color:rgb(255,255,255);">1.內存地址識別(“==”號識別)。 <br></p><p>2.根據equals()、hashCode()中的定義識別。</p><p><span style="font-size:14px;"><span style="color:rgb(51,51,51);background-color:rgb(255,255,255);">==是判斷兩個變量或實例是不是指向同一個內存空間 </span><br style="color:rgb(51,51,51);background-color:rgb(255,255,255);"><span style="color:rgb(51,51,51);background-color:rgb(255,255,255);">equals是判斷兩個變量或實例所指向的內存空間的值是不是相同 </span><br style="color:rgb(51,51,51);background-color:rgb(255,255,255);"><span style="color:rgb(51,51,51);background-color:rgb(255,255,255);">也就是說== 判斷是你比較值的地址 而equals比較的是你兩個數值是否相等。</span></span><br></p><p style="font-family:'-apple-system', 'SF UI Text', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', sans-serif, SimHei, SimSun;background-color:rgb(255,255,255);">在hibernate中，如果在同一session中根據相同查詢所得到的相同記錄，則它們會有相同的內存地址。但是如果是不同的session中查詢的相同記錄，它們的內存地址就會不同。因此，使用“==”來比較兩條記錄是否代表數據庫中的同一記錄是不可行的。如果有必要比較通過查詢後的內容是否相同，必須重寫equals()與hashCode()方法。</p><div class="dp-highlighter bg_java"><div class="bar"><div class="tools"><b>[java]</b> <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a><span data-mod="popu_168"> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 499px; top: 596px; width: 16px; height: 16px; z-index: 99;"><embed id="ZeroClipboardMovie_1" src="https://csdnimg.cn/public/highlighter/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="16" height="16" name="ZeroClipboardMovie_1" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=1&width=16&height=16" wmode="transparent"></div><div style="position: absolute; left: 499px; top: 596px; width: 16px; height: 16px; z-index: 99;"><embed id="ZeroClipboardMovie_2" src="https://csdnimg.cn/public/highlighter/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" width="16" height="16" name="ZeroClipboardMovie_2" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=2&width=16&height=16" wmode="transparent"></div></span><span data-mod="popu_169"> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a></span><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1" class="dp-j"><li class="alt"><span><span class="keyword">public</span><span> </span><span class="keyword">class</span><span> User { </span></span></li><li class=""><span> <span class="keyword">private</span><span> </span><span class="keyword">int</span><span> id; </span></span></li><li class="alt"><span> <span class="keyword">private</span><span> String username; </span></span></li><li class=""><span> <span class="keyword">private</span><span> String password; </span></span></li><li class="alt"><span> <span class="keyword">private</span><span> </span><span class="keyword">int</span><span> age; </span></span></li><li class=""><span> </span></li><li class="alt"><span> <span class="keyword">public</span><span> </span><span class="keyword">int</span><span> getId() { </span></span></li><li class=""><span> <span class="keyword">return</span><span> id; </span></span></li><li class="alt"><span> } </span></li><li class=""><span> </span></li><li class="alt"><span> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> setId(</span><span class="keyword">int</span><span> id) { </span></span></li><li class=""><span> <span class="keyword">this</span><span>.id = id; </span></span></li><li class="alt"><span> } </span></li><li class=""><span> </span></li><li class="alt"><span> <span class="keyword">public</span><span> String getUsername() { </span></span></li><li class=""><span> </span></li><li class="alt"><span> <span class="keyword">return</span><span> username; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> setUsername(String username) { </span></span></li><li class="alt"><span> <span class="keyword">this</span><span>.username = username; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="keyword">public</span><span> String getPassword() { </span></span></li><li class="alt"><span> <span class="keyword">return</span><span> password; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> setPassword(String password) { </span></span></li><li class="alt"><span> <span class="keyword">this</span><span>.password = password; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="keyword">public</span><span> </span><span class="keyword">int</span><span> getAge() { </span></span></li><li class="alt"><span> <span class="keyword">return</span><span> age; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> setAge(</span><span class="keyword">int</span><span> age) { </span></span></li><li class="alt"><span> <span class="keyword">this</span><span>.age = age; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="annotation">@Override</span><span> </span></span></li><li class="alt"><span> <span class="keyword">public</span><span> </span><span class="keyword">boolean</span><span> equals(Object otherObject) { </span></span></li><li class=""><span> <span class="comment">// 判斷內存地址是否相同</span><span> </span></span></li><li class="alt"><span> <span class="keyword">if</span><span> (</span><span class="keyword">this</span><span> == otherObject) { </span></span></li><li class=""><span> <span class="keyword">return</span><span> </span><span class="keyword">true</span><span>; </span></span></li><li class="alt"><span> } <span class="keyword">else</span><span> { </span></span></li><li class=""><span> <span class="comment">// 判斷是否爲User對象</span><span> </span></span></li><li class="alt"><span> <span class="keyword">if</span><span> (!(otherObject </span><span class="keyword">instanceof</span><span> User)) </span></span></li><li class=""><span> <span class="keyword">return</span><span> </span><span class="keyword">false</span><span>; </span></span></li><li class="alt"><span> } </span></li><li class=""><span> User user = (User) otherObject; </span></li><li class="alt"><span> <span class="comment">// 判斷各個屬性值是否相同</span><span> </span></span></li><li class=""><span> <span class="keyword">if</span><span> (id == user.id && username.equals(user.username) && password.equals(user.password) && age == user.age) { </span></span></li><li class="alt"><span> <span class="keyword">return</span><span> </span><span class="keyword">true</span><span>; </span></span></li><li class=""><span> } </span></li><li class="alt"><span> </span></li><li class=""><span> <span class="keyword">return</span><span> </span><span class="keyword">false</span><span>; </span></span></li><li class="alt"><span> } </span></li><li class=""><span> </span></li><li class="alt"><span> <span class="annotation">@Override</span><span> </span></span></li><li class=""><span> <span class="keyword">public</span><span> </span><span class="keyword">int</span><span> hashCode() { </span></span></li><li class="alt"><span> <span class="keyword">int</span><span> result; </span></span></li><li class=""><span> result = username.hashCode() + password.hashCode(); </span></li><li class="alt"><span> result = <span class="number">29</span><span> * age + result; </span></span></li><li class=""><span> <span class="keyword">return</span><span> result; </span></span></li><li class="alt"><span> } </span></li><li class=""><span> </span></li><li class="alt"><span>} </span></li></ol></div><pre class="java" name="code" style="display: none;">public class User {
private int id;
private String username;
private String password;
private int age;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public boolean equals(Object otherObject) {
// 判斷內存地址是否相同
if (this == otherObject) {
return true;
} else {
// 判斷是否爲User對象
if (!(otherObject instanceof User))
return false;
}
User user = (User) otherObject;
// 判斷各個屬性值是否相同
if (id == user.id && username.equals(user.username) && password.equals(user.password) && age == user.age) {
return true;
}
return false;
}
@Override
public int hashCode() {
int result;
result = username.hashCode() + password.hashCode();
result = 29 * age + result;
return result;
}
}
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