java 静态与非静态使用 this 和事件处理程序

Question

我正在尝试了解 java 的事件处理程序，并不断收到我创建的类型（静态/非静态）方法的错误。我试图编写的一些代码如下所示：

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

public class Main extends JFrame implements ActionListener{

  static private int[] intArray = new int[10000];
  static private int numOfInts = 0;
  static private int avg = 0;

  public static void main(String[] args) {

    //create main frame
    JFrame frame = new JFrame();
    frame.setTitle("Section V, question 2");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(350, 250);
    frame.setLayout(new GridLayout(4, 1));
    frame.setVisible(true);

  //create instruction label and add to frame
  Label instructions = new Label("Follow the instructions on the exam to use this program");
  frame.add(instructions);

  //create textfield for index entry and add to frame
  JTextField indexEntry = new JTextField();
  frame.add(indexEntry);

  //create button for average and add to frame
  JButton avgBtn = new JButton("Click for Average");
  frame.add(avgBtn);
  avgBtn.addActionListener(avgBtn);

  //create panel to display results and add to frame
  JPanel resultsPanel = new JPanel();
  resultsPanel.setBackground(Color.BLUE);
  frame.add(resultsPanel);

  //read in from file
  readFromFile();

  //compute average
  computeAverage();

  System.out.println(avg);

}

static private void readFromFile(){
  try{
    // Open the file that is the first
    // command line parameter
    FileInputStream fstream = new FileInputStream("numbers.dat");
    // Get the object of DataInputStream
    DataInputStream in = new DataInputStream(fstream);
    BufferedReader br = new BufferedReader(new InputStreamReader(in));
    String strLine;
    //Read File Line By Line
    int i = 0;
    while ((strLine = br.readLine()) != null)   {
      // Print the content on the console
      System.out.println (strLine);
      intArray[i] = Integer.parseInt(strLine);
      numOfInts++;
      i++;
    }
    //Close the input stream
    in.close();
    System.out.println ("numOfInts = " + numOfInts);
  }
  catch (Exception e){//Catch exception if any
    System.err.println("Error: " + e.getMessage());
  }
}

static private void computeAverage(){
  int sum = 0;

  for(int i = 0; i < numOfInts; i++)
    sum += intArray[i];

  avg = sum/numOfInts;

  //return avg;
}

public void actionPerformed(ActionEvent e){
      if(e.getSource() == avgBtn){
        computeAverage();
  }
}

}

应该设置一个 GUI，从文件中读取一些整数，然后在按下按钮时计算它们的平均值。但是，我不断遇到静态/非静态内容和事件处理程序的问题。我当前的错误是：
Main.java:35: javax.swing.AbstractButton 中的 addActionListener(java.awt.event.ActionListener) 无法应用于 (javax.swing.JButton)
avgBtn.addActionListener(avgBtn);

Main.java:91: 找不到符号
符号：变量 avgBtn
位置：主类
if(e.getSource() == avgBtn){

我知道编译器找不到 avgBtn 因为它是在另一个函数 (Main()) 中定义的，但是任何人都可以阐明如何将事件处理程序附加到它吗？尝试了“这个”也无济于事......提前致谢，如果您发现任何其他问题，我很想听听如何做得更好。

Answer 1

你的代码有点乱，编译的话会出现更多语法错误。
您不应该混合使用 swing/awt 组件，例如：在 swing 中不要使用 Label，使用 JLabel，而对于 Panel，则使用 JPanel。

请注意 swing 的“J”前缀，如果您想了解更多有关 Java（Swing）的信息，或者甚至阅读一些基础教程，也许您应该阅读书籍。

除非您了解静态方法的用途，否则不要使用静态方法。

无论如何，这里是最接近您想要的代码：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class Main extends JFrame implements ActionListener {
    private int[] intArray = new int[10000];
    private int numOfInts = 0;
    private int avg = 0;

    protected JButton avgBtn;
    protected JTextField indexEntry;
    protected JLabel instructions;
    protected JPanel resultsPanel;

    //constructor - construct the components here and do the initializations
    public Main(){
        //create main frame     
        this.setTitle("Section V, question 2");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setSize(350, 250);
        this.setLayout(new GridLayout(4, 1));
        //this.setVisible(true);

        //create instruction label and add to frame
        instructions = new JLabel("Follow the instructions on the exam to use this program");
        this.add(instructions);

        //create textfield for index entry and add to frame
        indexEntry = new JTextField();
        this.add(indexEntry);

        //create button for average and add to frame
        avgBtn = new JButton("Click for Average");
        this.add(avgBtn);
        avgBtn.addActionListener(this);

        //create panel to display results and add to frame
        resultsPanel = new JPanel();
        resultsPanel.setBackground(Color.BLUE);
        this.add(resultsPanel);

        //read in from file
        readFromFile();

        //compute average
        computeAverage();
        System.out.println(avg);
    }

    private void readFromFile() {
        try {
            // Open the file that is the first
            // command line parameter
            FileInputStream fstream = new FileInputStream("numbers.dat");
            // Get the object of DataInputStream
            DataInputStream in = new DataInputStream(fstream);
            BufferedReader br = new BufferedReader(new InputStreamReader(in));
            String strLine;
            //Read File Line By Line
            int i = 0;
            while ((strLine = br.readLine()) != null) {
                // Print the content on the console
                System.out.println (strLine);
                intArray[i] = Integer.parseInt(strLine);
                numOfInts++;
                i++;
            }
            //Close the input stream
            in.close();
            System.out.println ("numOfInts = " + numOfInts);
        }
        catch (Exception e) {
            //Catch exception if any
            System.err.println("Error: " + e.getMessage());
        }
    }
    private void computeAverage() {
        int sum = 0;
        for (int i = 0; i < numOfInts; i++)
        sum += intArray[i];
        avg = sum/numOfInts;
        //return avg;
    }

    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == avgBtn) {
            computeAverage();
        }
    }

    public static void main(String[] args) {
        Main m = new Main();
        m.setVisible(true);
    }
}