如何将数据库中的数据设置到组合框？
如何将数据库中的数据设置到组合框？
提问于 2021-07-17 14:28:52
在这段代码中，我使用1个JComboBox从数据库中获取数据，并将其放入组合框中。但它给出了一个例外，即ClassCastException。
package com.admin;
import java.awt.EventQueue;
import java.util.List;
import javax.swing.JFrame;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.entity.DepartmentTable;
import com.helper.FactoryProvider;
import javax.swing.JComboBox;
public class Demo {
private JFrame frame;
private static JComboBox comboBox;
private static SessionFactory factory;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Demo window = new Demo();
window.frame.setVisible(true);
factory = FactoryProvider.getFactory();
setCombobox();
} catch (Exception e) {
e.printStackTrace();
}
}
private void setCombobox() {
Session session = factory.openSession();
Query q = session.createQuery("select dept_name from
DepartmentTable");
List<DepartmentTable> list = q.list();
for (DepartmentTable dept : list) {
comboBox.addItem(dept.getDept_name());
}
}
});
}
public Demo() {
initialize();
}
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 816, 408);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
JComboBox comboBox = new JComboBox();
comboBox.setBounds(342, 55, 183, 35);
frame.getContentPane().add(comboBox);
}
}错误是：
java.lang.ClassCastException: class java.lang.String cannot be cast to class com.entity.DepartmentTable (java.lang.String is in module java.base of loader 'bootstrap'; com.entity.DepartmentTable is in unnamed module of loader 'app')
at com.admin.Demo$1.setCombobox(Demo.java:41)
at com.admin.Demo$1.run(Demo.java:30)
at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:316)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)回答 1
Stack Overflow用户
发布于 2021-07-19 11:25:35
每当我们试图将一个类从一种类型不正确地转换为另一种类型时，例如，当我们试图将父对象类型转换为子类型时，或者当我们试图将一个对象类型转换为它不是其实例的子类时，JVM就会自动引发这个异常。
package com.admin;
import java.awt.EventQueue;
import java.util.List;
import javax.swing.JFrame;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.entity.DepartmentTable;
import com.helper.FactoryProvider;
import javax.swing.JComboBox;
public class Demo {
private JFrame frame;
private static JComboBox comboBox;
private static SessionFactory factory;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Demo window = new Demo();
window.frame.setVisible(true);
factory = FactoryProvider.getFactory();
setCombobox();
} catch (Exception e) {
e.printStackTrace();
}
}
private void setCombobox() {
Session session = factory.openSession();
Query q = session.createQuery("from DepartmentTable");
List<DepartmentTable> list = q.list();
for (DepartmentTable dept : list) {
String str=(String)dept.getDept_name();
Object obj=(Object)str;
comboBox.addItem(obj);
}
}
});
}
public Demo() {
initialize();
}
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 816, 408);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
comboBox = new JComboBox();
comboBox.setBounds(342, 55, 183, 35);
frame.getContentPane().add(comboBox);
}}
ClassCastException的详细说明
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/68417993
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