java - 将 ActionListener 添加到 JButton

Question

当尝试实现 ActionListener 时，我收到以下错误

EmployeesApplet.java:5: error: EmployeesApplet is not abstract and does not override  
abstract method actionPerformed(ActionEvent) in ActionListener  
public class EmployeesApplet extends JApplet implements ActionListener   
   ^
1 error

我不想制作EmployeesApplet abstract，因为它不需要。我的代码如下，请注意，我注释掉了 implements ActionListener 并将 JButtons 添加为 ActionListener

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

public class EmployeesApplet extends JApplet //implements ActionListener 
{
  public JButton              sd   = new JButton ("Salaried");
  public JButton              hr   = new JButton ("Hourly");
  public JButton              cm   = new JButton ("Commissioned");
  public JButton              cl   = new JButton ("Clear"); 

  private final int    FIELDS      =  8,   
                       FIELD_WIDTH = 20;   

  private String[]     strings     = new String[FIELDS];
  private TextFieldWithLabel[] tf  = new TextFieldWithLabel[FIELDS];
  private JTextArea    ta          = new JTextArea(5,25); 

     public void init()
     {
      String[]  s = {"First Name", "Last Name", "Employee ID", "(a) Salaried: Weekly Salary", "(b1) Hourly 1: Rate Per Hour", 
                   "(b2) Hourly 2: Hours Worked" , "(c1) Commissioned: Rate", "(c2) Commissioned: Gross Sales" };

       //----------------------
       //  Set up the Structure
       //----------------------

       Container c = getContentPane();
       JPanel f   = new JPanel(new FlowLayout());
       JPanel b   = new JPanel(new BorderLayout(2,0));

       JPanel glb = new JPanel(new GridLayout(8,1,0,2));
       JPanel gtf = new JPanel(new GridLayout(8,1,0,2));
       JPanel flb = new JPanel(new FlowLayout());


       // Add FlowLayout to the container
       c.add(f);
       // Add BorderLayout to the FlowLayout
       f.add(b);

       //---------------------------------------
       //Add JPanels to the BorderLayout regions
       //---------------------------------------

       // Add JLables to GridLayout in West
       b.add(glb, BorderLayout.WEST);
       for (int i = 0; i < tf.length; i++)
       {
        tf[i] = new TextFieldWithLabel(s[i], FIELD_WIDTH);
        glb.add(tf[i].getLabel());
       }

       // Add JTextFeilds to GridLayout in East
       b.add(gtf, BorderLayout.EAST);
       for (int i = 0; i < tf.length; i++)
       {
        tf[i] = new TextFieldWithLabel(s[i], FIELD_WIDTH);
        tf[i].getTextField();
        gtf.add(tf[i].getTextField());
       }

       // Add JButtons to FlowLayout in South
       b.add(flb, BorderLayout.SOUTH);

       flb.add(sd);
       flb.add(hr);
       flb.add(cm);
       flb.add(cl);

       //sd.addActionListener(this);
       //hr.addActionListener(this);
       //cm.addActionListener(this);
       //cl.addActionListener(this);

       // Add JTextArea and make it not editable   
       f.add(ta);
       ta.setEditable(false);

     }

     public void readFields()
     {
     }

     public void fieldsExist()
     {
     }

     public void fieldsEmpty()
     {
     }

     public void actionPerformed()
     {
     }


}

Answer 1

您的 actionPerformed 方法需要一个 ActionEvent 作为参数:

public void actionPerformed(ActionEvent e) {

}

否则你不会覆盖the method defined in ActionListener - 您将只是创建一个新方法。由于 ActionListener 是一个接口(interface)，因此您需要实现该接口(interface)中定义的所有方法，因此会出现错误。

<小时/>

使用 ActionEvent 参数声明 actionPerformed 方法，以传递有关事件的方法详细信息(哪个组件触发了事件， action command 等) 。如果没有 ActionEvent 参数，就没有简单的方法来收集此类信息。执行操作时，会创建一个 ActionEvent 对象，并填充事件信息，然后调用 actionPerformed 方法，该方法是 ActionEvent 对象作为参数传入。