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Java:声明一个变量但说它不存在

转载 作者:行者123 更新时间:2023-12-01 06:36:11 29 4
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我正在尝试制作一个基本计算器(我还没有完成),但我收到一个错误,其中操作监听器说变量“add”不存在。我已经解析了所有内容等,但变量似乎没有正确声明,代码如下:

import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JOptionPane;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JTextField;

public class Gui extends JFrame{

private JButton reg;
private JButton reg2;
private JButton reg3;
private JButton reg4;
private JTextField text;
private JTextField text2;
private JTextField text3;
private JTextField text4;
private JTextField text5;
private JTextField text6;
private JTextField text7;
private JTextField text8;


public Gui(){
super("Buttons");
setLayout(new FlowLayout());



text = new JTextField("000000000000000000000");
text2 = new JTextField("000000000000000000000");
text3 = new JTextField("000000000000000000000");
text4 = new JTextField("000000000000000000000");
text5 = new JTextField("000000000000000000000");
text6 = new JTextField("000000000000000000000");
text7 = new JTextField("000000000000000000000");
text8 = new JTextField("000000000000000000000");
reg = new JButton("Add");
reg2 = new JButton("Divide");
reg3 = new JButton("Multiply");
reg4 = new JButton("Subtract");

add(text);
add(text2);
add(reg);
add(text3);
add(text4);
add(reg2);
add(text5);
add(text6);
add(reg3);
add(text7);
add(text8);
add(reg4);

String st = text.getText();
String st2 = text.getText();
String st3 = text.getText();
String st4 = text.getText();
String st5 = text.getText();
String st6 = text.getText();
String st7 = text.getText();
String st8 = text.getText();

int txt1 = Integer.parseInt(st);
int txt2 = Integer.parseInt(st2);
int txt3 = Integer.parseInt(st3);
int txt4 = Integer.parseInt(st4);
int txt5 = Integer.parseInt(st5);
int txt6 = Integer.parseInt(st6);
int txt7 = Integer.parseInt(st7);
int txt8 = Integer.parseInt(st8);

int add=txt1+txt2;
if(txt4>0){
int add2=txt3/txt4;
}
int add3=txt5*txt6;
int add4=txt7-txt8;


handlerClass handler = new handlerClass();
reg.addActionListener(handler);
reg2.addActionListener(handler);
reg3.addActionListener(handler);
reg4.addActionListener(handler);






}

public class handlerClass implements ActionListener{
public void actionPerformed(ActionEvent event){
if(event.getActionCommand()=="Add"){
JOptionPane.showMessageDialog(null, String.format("Answer: %s", add));
}
}
}
}

这是错误代码

Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem: 
add cannot be resolved to a variable

at Gui$handlerClass.actionPerformed(Gui.java:101)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem:
add cannot be resolved to a variable

at Gui$handlerClass.actionPerformed(Gui.java:101)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem:
add cannot be resolved to a variable

at Gui$handlerClass.actionPerformed(Gui.java:101)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

最佳答案

这个:

JOptionPane.showMessageDialog(null, String.format("Answer: %s", add));

尝试使用add作为变量。但是,该变量在 actionPerformed 方法中不存在。它是 Gui 构造函数中的一个本地变量。这有点令人困惑,因为 add 也是一个方法,但从根本上来说,问题在于您在本地声明的 add 变量构造函数中的内容稍后不存在。

另请注意此比较:

if(event.getActionCommand()=="Add")

可能的工作取决于您提供命令的方式,但它实际上只是比较字符串引用。您应该使用:

if (event.getActionCommand().equals("Add"))

或者如果操作命令可能为空(并且您不想费心检查):

if ("Add".equals(event.getActionCommand())

另请注意:

Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem: add cannot be resolved to a variable

表示您可能忽略了来自 Eclipse 的警告:“代码无法编译 - 您真的想尝试运行它吗?”

您不应该尝试运行无法编译的代码 - 您应该在尝试运行它之前修复编译时错误

关于Java:声明一个变量但说它不存在,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/10863011/

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