getSource（）-我在做什么錯呢？

Question

我不知道我在做什么錯。 只是編寫一個簡單的程序來測試游戲的概念，而我試圖使三個按鈕在單擊時具有三個不同的輸出。 但是，對於按鈕1，按鈕2和按鈕3，我收到一條錯誤消息，指出它們無法解析為變量。 我不知道該怎么辦。 我究竟做錯了什么？

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

ActionEvent和JButton還支持actionCommand屬性的概念。 除非另有說明，否則ActionEvent#getActionCommand將返回按鈕的文本，您可以使用JButton#setActionCommand方法更改此文本。

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，您將使用ActionEvent的actionCommand屬性...

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);
    }
}

Answer 2

JButton是在CodeTestingGround()中定義的，這意味着無法在該方法之外訪問它們。 當您嘗試從actionPerformed訪問它們時，JButton不在范圍內。

您可以通過簡單地移動聲明來解決此問題：

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 3

您的buttons不在詞法范圍內。 使它們成為字段，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!");

並從CodeTestingGround構造函數中刪除聲明和初始化。 類似於（或僅刪除三行）

// 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);
// ...