投射对象时 event.getItem() 和 comboBox.getSelectedItem() 有什么区别
What is difference between event.getItem() and comboBox.getSelectedItem() while casting the object
我有一个带有组合框的面板。我正在向组合框添加 ID 号。但在添加任何 id 之前，我添加了一个空字符串以了解没有选择 id。
JComboBox jcPatientIds;
JPanel patientPanel;
public void updateIdsInComboBoxes(ArrayList<Integer> items)
{
getJcPatientIds().addItem("");
if (items.size() > 0)
{
for (Integer item : items)
{
getJcPatientIds().addItem(item);
}
}
getPatientPanel().add(getJcPatientIds());
}
public JComboBox getJcPatientIds()
{
if(jcPatientIds == null)
{
jcPatientIds = new JComboBox();
jcPatientIds.setBounds(250, 20, 100, 20);
}
return jcPatientIds;
}
public JPanel getPatientPanel()
{
if(patientPanel == null)
{
patientPanel = new JPanel();
}
return patientPanel;
}
现在，我有这样的监听器 class。它工作正常，没有任何错误
@Override
public void itemStateChanged(ItemEvent e)
{
/*The event triggers for both deselected and selected item
Here only the selected event will be triggered with value 1
deselected event has a value 2*/
if (e.getStateChange() == 1)
{
if (e.getItem().equals(""))
{
// Some stuff
}
else
{
System.out.println((int) e.getItem());
// Some other stuff
}
}
}
但是，如果我在 Combobox 上使用 getSelectedItem。我收到 ClassCastException。这里有什么问题
@Override
public void itemStateChanged(ItemEvent e)
{
if (getJcPatientIds.getSelectedItem().equals(""))
{
// Some stuff
}
else
{
System.out.println((int) getJcPatientIds.getSelectedItem()); // Here I am getting ClassCastException
// Some other stuff
}
}
}
错误
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
at hospitalApp.common.PatientController.itemStateChanged(PatientController.java:71)
at javax.swing.JComboBox.fireItemStateChanged(JComboBox.java:1225)
at javax.swing.JComboBox.selectedItemChanged(JComboBox.java:1273)
at javax.swing.JComboBox.contentsChanged(JComboBox.java:1329)
at javax.swing.AbstractListModel.fireContentsChanged(AbstractListModel.java:118)
at javax.swing.DefaultComboBoxModel.setSelectedItem(DefaultComboBoxModel.java:93)
at javax.swing.JComboBox.setSelectedItem(JComboBox.java:578)
at javax.swing.JComboBox.setSelectedIndex(JComboBox.java:624)
at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(BasicComboPopup.java:835)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:290)
at java.awt.Component.processMouseEvent(Component.java:6516)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at javax.swing.plaf.basic.BasicComboPopup.processMouseEvent(BasicComboPopup.java:499)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4872)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:747)
at java.awt.EventQueue.access0(EventQueue.java:103)
at java.awt.EventQueue.run(EventQueue.java:706)
at java.awt.EventQueue.run(EventQueue.java:704)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue.run(EventQueue.java:720)
at java.awt.EventQueue.run(EventQueue.java:718)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:717)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
你不能像 (int)(String_val)
那样将 String 转换为 int
System.out.println((int) getJcPatientIds.getSelectedItem());
这样改
Integer.parseInt(getJcPatientIds.getSelectedItem());
同样，我会避免在组合框中同时填充整数和字符串。坚持使用 Integer，实际上将您的 JComboBox 声明为使用 Integer 作为其通用类型的通用对象：JComboBox<Integer>。为空元素添加一个空值，然后检查空值：
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
public class Foo2 extends JPanel {
DefaultComboBoxModel<Integer> jcPtIdModel = new DefaultComboBoxModel<>();
JComboBox<Integer> jcPtIdCombo = new JComboBox<>(jcPtIdModel);
public Foo2(List<Integer> ids) {
if (ids != null) {
updateIds(ids);
}
add(jcPtIdCombo);
jcPtIdCombo.addItemListener(new MyItemListener());
}
public void updateIds(List<Integer> ids) {
jcPtIdModel.removeAllElements();
jcPtIdModel.addElement(null);
for (Integer id : ids) {
jcPtIdModel.addElement(id);
}
}
private class MyItemListener implements ItemListener {
@Override
public void itemStateChanged(ItemEvent e) {
//!! if (jcPatientIds.getSelectedItem().equals("")) {
if (jcPtIdCombo.getSelectedItem() == null) {
// Some stuff
} else {
// Here I am getting ClassCastException
System.out.println((int) jcPtIdCombo.getSelectedItem());
// Some other stuff
}
}
}
private static void createAndShowGui() {
ArrayList<Integer> items = new ArrayList<>();
for (int i = 0; i < 10; i++) {
items.add(i);
}
Foo2 mainPanel = new Foo2(items);
JFrame frame = new JFrame("Foo2");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
我还看到你在使用 setBounds(...)，我强烈建议你不要这样做。虽然 null 布局和 setBounds() 对于 Swing 新手来说似乎是创建复杂 GUI 的最简单和最好的方法，但您创建的 Swing GUI 越多，您在使用它们时 运行 就会遇到更严重的困难。它们不会在 GUI 调整大小时调整组件的大小，它们是皇家 来增强或维护的，当放置在滚动窗格中时它们会完全失败，当在所有平台或不同的屏幕分辨率上查看时它们看起来很糟糕从原来的。
我有一个带有组合框的面板。我正在向组合框添加 ID 号。但在添加任何 id 之前，我添加了一个空字符串以了解没有选择 id。
JComboBox jcPatientIds;
JPanel patientPanel;
public void updateIdsInComboBoxes(ArrayList<Integer> items)
{
getJcPatientIds().addItem("");
if (items.size() > 0)
{
for (Integer item : items)
{
getJcPatientIds().addItem(item);
}
}
getPatientPanel().add(getJcPatientIds());
}
public JComboBox getJcPatientIds()
{
if(jcPatientIds == null)
{
jcPatientIds = new JComboBox();
jcPatientIds.setBounds(250, 20, 100, 20);
}
return jcPatientIds;
}
public JPanel getPatientPanel()
{
if(patientPanel == null)
{
patientPanel = new JPanel();
}
return patientPanel;
}
现在，我有这样的监听器 class。它工作正常，没有任何错误
@Override
public void itemStateChanged(ItemEvent e)
{
/*The event triggers for both deselected and selected item
Here only the selected event will be triggered with value 1
deselected event has a value 2*/
if (e.getStateChange() == 1)
{
if (e.getItem().equals(""))
{
// Some stuff
}
else
{
System.out.println((int) e.getItem());
// Some other stuff
}
}
}
但是，如果我在 Combobox 上使用 getSelectedItem。我收到 ClassCastException。这里有什么问题
@Override
public void itemStateChanged(ItemEvent e)
{
if (getJcPatientIds.getSelectedItem().equals(""))
{
// Some stuff
}
else
{
System.out.println((int) getJcPatientIds.getSelectedItem()); // Here I am getting ClassCastException
// Some other stuff
}
}
}
错误
Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
at hospitalApp.common.PatientController.itemStateChanged(PatientController.java:71)
at javax.swing.JComboBox.fireItemStateChanged(JComboBox.java:1225)
at javax.swing.JComboBox.selectedItemChanged(JComboBox.java:1273)
at javax.swing.JComboBox.contentsChanged(JComboBox.java:1329)
at javax.swing.AbstractListModel.fireContentsChanged(AbstractListModel.java:118)
at javax.swing.DefaultComboBoxModel.setSelectedItem(DefaultComboBoxModel.java:93)
at javax.swing.JComboBox.setSelectedItem(JComboBox.java:578)
at javax.swing.JComboBox.setSelectedIndex(JComboBox.java:624)
at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(BasicComboPopup.java:835)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:290)
at java.awt.Component.processMouseEvent(Component.java:6516)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at javax.swing.plaf.basic.BasicComboPopup.processMouseEvent(BasicComboPopup.java:499)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4872)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:747)
at java.awt.EventQueue.access0(EventQueue.java:103)
at java.awt.EventQueue.run(EventQueue.java:706)
at java.awt.EventQueue.run(EventQueue.java:704)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue.run(EventQueue.java:720)
at java.awt.EventQueue.run(EventQueue.java:718)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:717)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
你不能像 (int)(String_val)
System.out.println((int) getJcPatientIds.getSelectedItem());
这样改
Integer.parseInt(getJcPatientIds.getSelectedItem());
同样，我会避免在组合框中同时填充整数和字符串。坚持使用 Integer，实际上将您的 JComboBox 声明为使用 Integer 作为其通用类型的通用对象：JComboBox<Integer>。为空元素添加一个空值，然后检查空值：
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
public class Foo2 extends JPanel {
DefaultComboBoxModel<Integer> jcPtIdModel = new DefaultComboBoxModel<>();
JComboBox<Integer> jcPtIdCombo = new JComboBox<>(jcPtIdModel);
public Foo2(List<Integer> ids) {
if (ids != null) {
updateIds(ids);
}
add(jcPtIdCombo);
jcPtIdCombo.addItemListener(new MyItemListener());
}
public void updateIds(List<Integer> ids) {
jcPtIdModel.removeAllElements();
jcPtIdModel.addElement(null);
for (Integer id : ids) {
jcPtIdModel.addElement(id);
}
}
private class MyItemListener implements ItemListener {
@Override
public void itemStateChanged(ItemEvent e) {
//!! if (jcPatientIds.getSelectedItem().equals("")) {
if (jcPtIdCombo.getSelectedItem() == null) {
// Some stuff
} else {
// Here I am getting ClassCastException
System.out.println((int) jcPtIdCombo.getSelectedItem());
// Some other stuff
}
}
}
private static void createAndShowGui() {
ArrayList<Integer> items = new ArrayList<>();
for (int i = 0; i < 10; i++) {
items.add(i);
}
Foo2 mainPanel = new Foo2(items);
JFrame frame = new JFrame("Foo2");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
我还看到你在使用 setBounds(...)，我强烈建议你不要这样做。虽然 null 布局和 setBounds() 对于 Swing 新手来说似乎是创建复杂 GUI 的最简单和最好的方法，但您创建的 Swing GUI 越多，您在使用它们时 运行 就会遇到更严重的困难。它们不会在 GUI 调整大小时调整组件的大小，它们是皇家 来增强或维护的，当放置在滚动窗格中时它们会完全失败，当在所有平台或不同的屏幕分辨率上查看时它们看起来很糟糕从原来的。