Question

我正在玩JFrames以获得乐趣，并且无法让面板显示静态变量。我很感激任何帮助。这是我正在使用的代码：

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

public class JButtonTester
{
    static int counter = 0;
    public static void main(String[]args)
    {
        class ClickCounter implements ActionListener
        {
            public void actionPerformed(ActionEvent event)
            {
                counter++;
                System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment");
            }
        }
        class ClickDecrement implements ActionListener
        {
            public void actionPerformed(ActionEvent event)
            {
                counter--;
                System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment");
            }
        }
        JFrame firstFrame = new JFrame();
        JLabel counter = new JLabel("Count: " + counter);
        JPanel firstPanel = new JPanel();

        JButton firstButton = new JButton("Click me to increase your count!");
        firstPanel.add(firstButton);
        ActionListener firstListener = new ClickCounter();
        firstButton.addActionListener(firstListener);

        JButton secondButton = new JButton("Click me to decrease your count!");
        firstPanel.add(secondButton);
        ActionListener secondListener = new ClickDecrement();
        secondButton.addActionListener(secondListener);

        firstFrame.add(firstPanel);
        firstFrame.setSize(200, 120);
        firstFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        firstFrame.setVisible(true);
    }
}

我想要访问的变量是“counter。”

Answer 1

从另一个类访问静态变量意味着使用类的名称继续变量名，因为static意味着它是一个类变量。因此，由于counter是JButtonTester类的静态变量，要从另一个类访问计数器，你会说JButtonTester.counter

JLabel counter = new JLabel("Count: " + JButtonTester.counter);

Answer 2

你排在这里是错的

JLabel counter = new JLabel("Count: " + counter);

counter是对您正在创建的JLabel的引用，使用不同的变量名称

Answer 3

您需要做的几件事：

重命名字段：您有两个名为counter的变量。
其次，您需要将JLabel移到actionPerformed方法之上并声明final，以便您可以在actionPerformed方法中访问它。
我没有看到您在面板中添加JLabel的位置，因此我添加了该行

这应该做你想要的：

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

public class JButtonTester {

    static int counter = 0;

    public static void main(String[] args) {

        final JLabel counter_label = new JLabel();
        class ClickCounter implements ActionListener {

            public void actionPerformed(ActionEvent event) {
                counter++;
                System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment");
                counter_label.setText("Count: " + counter);
            }
        }
        class ClickDecrement implements ActionListener {

            public void actionPerformed(ActionEvent event) {
                counter--;
                System.out.println("Congratulations, you clicked a button " + counter + " time(s)! This might just be your greatest accomplishment");
                counter_label.setText("Count: " + counter);
            }
        }
        JFrame firstFrame = new JFrame();
        JPanel firstPanel = new JPanel();
        firstPanel.add(counter_label);

        JButton firstButton = new JButton("Click me to increase your count!");
        firstPanel.add(firstButton);
        ActionListener firstListener = new ClickCounter();
        firstButton.addActionListener(firstListener);

        JButton secondButton = new JButton("Click me to decrease your count!");
        firstPanel.add(secondButton);
        ActionListener secondListener = new ClickDecrement();
        secondButton.addActionListener(secondListener);

        firstFrame.add(firstPanel);
        firstFrame.setSize(200, 120);
        firstFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        firstFrame.setVisible(true);
    }
}

让JLabel可以访问静态变量吗？

3 个答案: