getSource() - 我在这里做错了什么？

Question

我不知道我在这里做错了什么。只是制作一个简单的程序来测试游戏的概念，我试图让三个按钮在单击时具有三个不同的输出。但是，对于按钮一、二和三，我收到一条错误消息，指出它们无法解析为变量。我不知道该怎么办。我做错了什么？

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener; 

public class CodeTestingGround extends JFrame implements ActionListener {

public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException 
{
    UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
    new CodeTestingGround();

}

public CodeTestingGround() {

    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    JFrame frameone = new JFrame();
    frameone.setLayout(null);

    frameone.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frameone.setLocation(screenSize.width / 3, screenSize.height / 3);

    JButton buttonone = new JButton("Click here to download viruses!");
    JButton buttontwo = new JButton("Click here to get scammed!");
    JButton buttonthree = new JButton("Click here to get hacked!");
    buttonone.setBounds(10, 10, 260, 30);
    buttontwo.setBounds(10, 50, 260, 30);
    buttonthree.setBounds(10, 90, 260, 30);
    buttonone.addActionListener(this);
    buttontwo.addActionListener(this);
    buttonthree.addActionListener(this);
    frameone.add(buttonone);
    frameone.add(buttontwo);
    frameone.add(buttonthree);
    frameone.pack();
    frameone.setVisible(true);
    frameone.setSize(300, 400);

}

public void actionPerformed(ActionEvent event) {
    Object control = event.getSource();
    if (control == buttonone) { // error right here
        JOptionPane.showMessageDialog(null, "Viruses sucessfully downloaded!", "Important Alert", JOptionPane.WARNING_MESSAGE);
    }
    else if (control == buttontwo) { // error right here
        JOptionPane.showMessageDialog(null, "YOU HAVE WON A MILLION DOLLARS!!! Enter you credit card information to claim your prize.", "YOU ARE WIN", JOptionPane.INFORMATION_MESSAGE);
    }
    else if (control == buttonthree) { // error right here
        JOptionPane.showMessageDialog(null, "You have been haxored", "get hacked", JOptionPane.ERROR_MESSAGE);
    }



}

}

Answer 1

JButtons 在CodeTestingGround() 中定义，这意味着它们不能在该方法之外访问。当您尝试从 actionPerformed 访问它们时，JButton 超出范围。

您可以通过简单地移动声明来解决此问题：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener; 

public class CodeTestingGround extends JFrame implements ActionListener {

//Declarations go here instead
JButton buttonone;
JButton buttontwo;
JButton buttonthree;

public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, UnsupportedLookAndFeelException 
{
    UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
    new CodeTestingGround();

}

public CodeTestingGround() {

    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    JFrame frameone = new JFrame();
    frameone.setLayout(null);

    frameone.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frameone.setLocation(screenSize.width / 3, screenSize.height / 3);

    buttonone = new JButton("Click here to download viruses!");
    buttontwo = new JButton("Click here to get scammed!");
    buttonthree = new JButton("Click here to get hacked!");
    buttonone.setBounds(10, 10, 260, 30);
    buttontwo.setBounds(10, 50, 260, 30);
    buttonthree.setBounds(10, 90, 260, 30);
    buttonone.addActionListener(this);
    buttontwo.addActionListener(this);
    buttonthree.addActionListener(this);
    frameone.add(buttonone);
    frameone.add(buttontwo);
    frameone.add(buttonthree);
    frameone.pack();
    frameone.setVisible(true);
    frameone.setSize(300, 400);

}

public void actionPerformed(ActionEvent event) {
    Object control = event.getSource();
    if (control == buttonone) { // error right here
        JOptionPane.showMessageDialog(null, "Viruses sucessfully downloaded!", "Important Alert", JOptionPane.WARNING_MESSAGE);
    }
    else if (control == buttontwo) { // error right here
        JOptionPane.showMessageDialog(null, "YOU HAVE WON A MILLION DOLLARS!!! Enter you credit card information to claim your prize.", "YOU ARE WIN", JOptionPane.INFORMATION_MESSAGE);
    }
    else if (control == buttonthree) { // error right here
        JOptionPane.showMessageDialog(null, "You have been haxored", "get hacked", JOptionPane.ERROR_MESSAGE);
    }
}
}

Answer 2

您的 buttons 不在词法范围内。使它们成为字段，例如

private JButton buttonone = new JButton("Click here to download viruses!");
private JButton buttontwo = new JButton("Click here to get scammed!");
private JButton buttonthree = new JButton("Click here to get hacked!");

并从CodeTestingGround 构造函数中删除声明和初始化。类似的东西（或只是删除三行）

// JButton buttonone = new JButton("Click here to download viruses!");
// JButton buttontwo = new JButton("Click here to get scammed!");
// JButton buttonthree = new JButton("Click here to get hacked!");
buttonone.setBounds(10, 10, 260, 30);
buttontwo.setBounds(10, 50, 260, 30);
buttonthree.setBounds(10, 90, 260, 30);
// ...

Answer 3

ActionEvent 和JButton 也支持actionCommand 属性的概念。除非另有说明，ActionEvent#getActionCommand 将返回按钮的文本，您可以使用 JButton#setActionCommand 方法更改此内容

JButton buttonone = new JButton("Click here to download viruses!");
buttonone.setActionCommand("bad");
JButton buttontwo = new JButton("Click here to get scammed!");
buttonone.setActionCommand("ugly");
JButton buttonthree = new JButton("Click here to get hacked!");
buttonone.setActionCommand("hacked");

然后您将使用ActionEvent 的actionCommand 属性...

public void actionPerformed(ActionEvent event) {
    String cmd = event.getActionCommand();
    if ("bad".equals(cmd)) { // error right here
        JOptionPane.showMessageDialog(null, "Viruses sucessfully downloaded!", "Important Alert", JOptionPane.WARNING_MESSAGE);
    }
    else if ("ugly".equals(cmd)) { // error right here
        JOptionPane.showMessageDialog(null, "YOU HAVE WON A MILLION DOLLARS!!! Enter you credit card information to claim your prize.", "YOU ARE WIN", JOptionPane.INFORMATION_MESSAGE);
    }
    else if ("hacked".equals(cmd)) { // error right here
        JOptionPane.showMessageDialog(null, "You have been haxored", "get hacked", JOptionPane.ERROR_MESSAGE);
    }
}