Java 无法传递在“public void actionPerformed(ActionEvent事件)”中声明的变量
我正在创建WindowBuilder GUI,需要将使用单选按钮创建的变量传递给EventHandler类,以便在进一步处理中使用。单选按钮事件的输出成功;但是,在中的actionPerformed方法中声明的变量df在EventHanler类中没有解析。任何帮助都将不胜感激Java 无法传递在“public void actionPerformed(ActionEvent事件)”中声明的变量,java,swing,events,event-handling,Java,Swing,Events,Event Handling,我正在创建WindowBuilder GUI,需要将使用单选按钮创建的变量传递给EventHandler类,以便在进一步处理中使用。单选按钮事件的输出成功;但是,在中的actionPerformed方法中声明的变量df在EventHanler类中没有解析。任何帮助都将不胜感激 public TestClass() { /* INSERT RADIOBUTTON INTO FRAME. */ JRadioButton rdbtnNo = new JRadioButton("No"
public TestClass() {
/* INSERT RADIOBUTTON INTO FRAME. */
JRadioButton rdbtnNo = new JRadioButton("No");
rdbtnNo.setFont(new Font("Tahoma", Font.BOLD, 12));
rdbtnNo.setBounds(332, 509, 63, 23);
frame.getContentPane().add(rdbtnNo);
/* LISTEN FOR RADIOBUTTON BUTTON. */
rdbtnNo.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
String command = event.getActionCommand();
System.out.println(command);
int df = 20;
}
});
rdbtn.setActionCommand("event");
rdbtn.addActionListener(new EventHandler());
}
public class EventHandler implements ActionListener {
public void actionPerformed(ActionEvent event) {
System.out.println(df);
}
}
第一件事是去掉匿名内部类,改用lambdas。它使您的代码更易于理解
public TestClass() {
/* INSERT RADIOBUTTON INTO FRAME. */
JRadioButton rdbtnNo = new JRadioButton("No");
rdbtnNo.setFont(new Font("Tahoma", Font.BOLD, 12));
rdbtnNo.setBounds(332, 509, 63, 23);
frame.getContentPane().add(rdbtnNo);
/* LISTEN FOR RADIOBUTTON BUTTON. */
rdbtnNo.addActionListener(event -> pressedTheButton(event));
rdbtn.setActionCommand("event");
rdbtn.addActionListener(new EventHandler());
}
public void pressedTheButton(ActionEvent event) {
String command = event.getActionCommand();
System.out.println(command);
int df = 20;
printStuff(df);
}
public void printStuff(int input) {
System.out.println(input);
}
///DELETE THIS. This is unneeded, use Java 8 stuff, it's awesome////
public class EventHandler implements ActionListener {
public void actionPerformed(ActionEvent event) {
System.out.println(df);
}
}
在你的代码中。
您也有其他错误,但当您在下面声明了该内部类时,必须在addActionListener方法中实例化它以利用它。无法在其他类中解析它,因为该变量的范围仅在该方法中:
public void actionPerformed(ActionEvent event) {
String command = event.getActionCommand();
System.out.println(command);
int df = 20;
}
在中的actionPerformed方法中声明的变量df未在EventHanler类中解析
这是因为。在您的示例中,您将df声明为传递给AddActionListener的匿名内部类的actionPerformedActionEvent方法中的局部变量。局部变量只能在创建它们的代码块内访问。这意味着除了actionPerformedActionEvent方法之外,您的df变量不能在任何其他地方访问
解决这一问题的第一步是将df作为测试类中的实例变量,以便可以在actionPerformedActionEvent方法内外访问它
这里有两种可能的方法:
对两个按钮使用第二个匿名内部类
public class Test {
private int df;
public Test() {
// ...
final JButton button = new JButton("Click Me");
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
df = 20;
}
});
final JButton button2 = new JButton("Click Me Again");
button2.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
if(df == 20) { // got instance
// TODO do a thing
}
}
});
// ...
}
}
将df传递给EventHandler的构造函数
旁注:不要使用空布局!请参见TestClass方法是否返回任何内容?了解变量作用域:是否尝试添加2个EventListener?
public class Test {
private int df;
public Test() {
// ...
final JButton button = new JButton("Click Me");
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
df = 20;
}
});
final JButton button2 = new JButton("Click Me Again");
button2.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
if(df == 20) { // got instance
// TODO do a thing
}
}
});
// ...
}
}
public class Test {
private int df;
public Test() {
// ... button1 ...
final JButton button2 = new JButton("Click Me Again");
button2.addActionListener(new EventHandler());
// ...
}
}
// different file
public class EventHandler implements ActionListener {
private int df;
public EventHandler(int df) {
this.df = df; // got instance
}
@Override
public void actionPerformed(ActionEvent e) {
if(df == 20) {
// TODO do a thing
}
}
}