Java不能實例化類型ActionListener

Question

即時嘗試添加一個ActionListener到我的按鈕爲我的計算器我正在做。問題是當我嘗試創建一個ActionListener時，Im被顯示錯誤。我在一個類中嘗試過，然後我創建了一個監聽器類來查看是否有幫助。這裏是我的代碼：

package main; 

import java.awt.Color; 
import java.awt.FlowLayout; 
import java.awt.Font; 
import java.awt.event.ActionListener; 
import java.io.IOException; 
import javax.swing.JButton; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.JTextField; 

public abstract class Main extends JFrame implements Listener{ 
public static void main(String[] args) throws IOException{ 
//Main variables 
String dis = "0"; 
double ans = Double.parseDouble(dis); 


//Making frames 
JFrame frame = new JFrame("Calculator"); 
JPanel panel = new JPanel(); 

//Buttons 
JButton enter = new JButton("Enter"); 
JButton sub = new JButton("-"); 
JButton add = new JButton("+"); 
JButton div = new JButton("÷"); 
JButton mult = new JButton("*"); 
JTextField text = new JTextField(dis); 

//Font 
Font bigFont = text.getFont().deriveFont(Font.PLAIN, 30f); 
Font butf = text.getFont().deriveFont(Font.PLAIN, 20f); 
//Methods 
panel.setLayout(new FlowLayout()); 
panel.add(text); 
panel.setSize(590, 100); 
text.setColumns(22); 
text.setFont(bigFont); 
text.setHorizontalAlignment(JTextField.RIGHT); 
text.setEditable(false); 
enter.setForeground(Color.RED); 
sub.setForeground(Color.RED); 
div.setForeground(Color.RED); 
mult.setForeground(Color.RED); 
add.setForeground(Color.RED); 
//Buttons Methods 
enter.setBounds(470, 450, 100, 150); 
sub.setBounds(470, 350, 100, 90); 
div.setBounds(470, 250, 100, 90); 
mult.setBounds(470, 150, 100, 90); 
add.setBounds(470, 50, 100, 90); 
enter.setFont(butf); 
sub.setFont(butf); 
div.setFont(butf); 
mult.setFont(butf); 
add.setFont(butf); 
//Frame 
frame.add(div); 
frame.add(mult); 
frame.add(sub); 
frame.add(enter); 
frame.add(add); 
frame.add(panel); 
frame.setSize(600, 650); 
frame.setLocationRelativeTo(null); 
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
frame.setVisible(true); 


//extra 
text.setSize(1000, 100); 


//Actions 

}}

package main; 

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

public interface Listener extends ActionListener { 
//Throwing error here 'Cant instantiate the type ActionListener' 
ActionListener al = new ActionListener(); 
public default void actionPerformed(ActionEvent e){ 

    } 



} 

任何人都知道如何解決這個問題？

Answer 1

要聲明一個ActionListener使用

public class Listener implements ActionListener 
{ 
    public void actionPerformed(ActionEvent e) 
    { 
     //dostuff 
    } 
} 

Answer 2

• ActionListener是interface，它不能被實例化，沒有提供一個具體的實現它的合同
• interface s不能包含實例字段

簡而言之，它應該看起來更像...

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

public interface Listener extends ActionListener { 

    public default void actionPerformed(ActionEvent e) { 
    } 

} 

你也可以想有在

• How to Write an Action Listeners
• What Is an Interface?
• 的Interfaces線索仔細一看

在Swing中，你應該確保你的UI是隻能在事件分派線程的上下文中創建和操作。看看Initial Threads更多細節

你也將是非常失望佈局的結果，看看Laying Out Components Within a Container更好的解決方案