java - 如何显示按钮并在用户按下按钮时显示随机数？

Question

您好，我一直在研究如何使按钮显示随机数。这就是我现在所处的位置。我不知道随机数生成器代码会去哪里。如果我把它放在 ActionListener 之前，它只会发布在按钮旁边，而不是在按下按钮时出现。它不断给我错误消息

错误: 无法引用封闭范围内定义的非最终局部变量 num1。

请引用以下代码:

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

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JOptionPane;
import java.util.Random;

public class myTest {

    public static void main(String[] args) {

        Random generator = new Random();
        int num1;

        final JFrame frame = new JFrame();
        JPanel panel = new JPanel();

        num1 = generator.nextInt(101);
        System.out.println("the random number is:" +num1);

          JButton button1 = new JButton("Push Me!");

        frame.add(panel);
        panel.add(button1);
        frame.setVisible(true);

        button1.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent arg0) {
           num1 = generator.nextInt(101);
        System.out.println("the random number is:" +num1);
            }
        });

    }

}

Answer 1

您可以在JButton 上调用setText。另外，不要忘记设置默认关闭操作。您无法从外部范围引用num1。我想你想要类似的东西

Random generator = new Random();
final JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();

int num1 = generator.nextInt(101);
System.out.println("the random number is:" + num1);

JButton button1 = new JButton(String.format("Push Me! %d", num1));
frame.add(panel);
panel.add(button1);
frame.pack();
frame.setVisible(true);

button1.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0) {
        int num1 = generator.nextInt(101);
        System.out.println("the random number is:" + num1);
        button1.setText(String.format("Push Me! %d", num1));
    }
});