Question

我只是在尝试编写有趣的代码，但是我被卡住了。我试图在一个类A中创建3个JButton，然后在另一个类B中调用这些按钮，然后在类B中添加ActionListeners。所以基本上，我只在抽象类A中创建按钮，然后在扩展类的类B中调用它们A和BI类中的东西用这些按钮填充。听起来很简单，但是我无法弄清楚。

A类：

public abstract class Activity implements ActionListener {

        public static JFrame frame;`
        public static JPanel panel;
        public static JLabel label;
        public JButton buttonleft;
        public JButton buttonmid;
        public JButton buttonright;

    protected void makenButtons(String textlinks, String textmidden, String textrechts) {
                JButton buttonleft = new JButton(textlinks);
                JButton buttonmid = new JButton(textmidden);
                JButton buttonright = new JButton(textrechts);
                panel.add(buttonleft);
                panel.add(buttonmid);
                if (textrechts!=null) {
                panel.add(buttonright);
            }

B类：

package hi;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JPanel;

public class MainActivity extends Activity{

    public static void main(String[] args) {
        Activity.makenFrame(380,120,"Choose mode");
        Activity.makenLabel("Choose a work mode: ");
        Activity.makenOpties("Run as server", "Run as client");
        //Activity.makenButtons("Start","Exit",null);
        MainActivity a = new MainActivity();
        a.actiesButtons("Start","Exit");
        Activity.toevoegenpanel();
        }

    public void actiesButtons(String textleft, String textright) {
        JButton buttonleft  = super.buttonleft;
        JButton buttonmid  = super.buttonmid;
        buttonleft.setText(textleft);
        buttonmid.setText(textright);
        buttonleft.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent event) {
            if (event.getSource() == buttonleft) {
                System.out.print("Hi");
        }
     }          
});
        buttonmid.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent event) {
            if (event.getSource() == buttonright) {
                System.exit(0);             }
        }           
    });
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub

    }
}

I deleted some not-important stuff. So basically I just like to know how to call the JButtons in class B. I tried:


 JButton buttonleft  = super.buttonleft;
        JButton buttonmid  = super.buttonmid;

但是这给了我一个nullpointerexception。预先感谢！

编辑：我知道我的问题是例外，我只是不知道如何解决它:( 有人可以为我写一些快速的伪代码，如何在一个类中创建一个按钮，在另一个类中调用该按钮吗？：）

Java JButton在不同的类中创建和调用

0 个答案: