Java中如何在静态上下文中调用JFrame的非静态方法

错误原因 #

你遇到的编译错误是因为在非静态成员方法Button1_ActionPerformed中，直接用类名Fangmich调用了非静态方法getWidth()、getHeight()。非静态方法属于类的实例对象，不能通过类名直接访问。

修复方案 #

由于Button1_ActionPerformed本身就是Fangmich类的非静态成员方法，直接调用当前实例的对应方法即可，无需用类名引用，修改对应代码行：

// 修改前（错误）
int maxX = Fangmich.getWidth() - Button1.getWidth();
int maxY = Fangmich.getHeight() - Button1.getHeight();

// 修改后（正确）
int maxX = getWidth() - Button1.getWidth();
int maxY = getHeight() - Button1.getHeight();

优化建议 #

1. Random对象无需重复创建，单个实例即可生成多次随机数
2. 若要避免按钮被窗口标题栏、边框遮挡，可使用内容面板的宽高计算边界，效果更准确：

int maxX = getContentPane().getWidth() - Button1.getWidth();
int maxY = getContentPane().getHeight() - Button1.getHeight();

修改后完整可运行代码 #

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

public class Fangmich extends JFrame {
  private JButton Button1 = new JButton();
  private Random random = new Random();
  
  public Fangmich() { 
    super();
    setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
    int frameWidth = 300; 
    int frameHeight = 300;
    setSize(frameWidth, frameHeight);
    Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
    int x = (d.width - getSize().width) / 2;
    int y = (d.height - getSize().height) / 2;
    setLocation(x, y);
    setTitle("Fangmich");
    setResizable(true);
    Container cp = getContentPane();
    cp.setLayout(null);
    
    Button1.setBounds(0, 0, 73, 41);
    Button1.setText("Fang mich!");
    Button1.setMargin(new Insets(2, 2, 2, 2));
    Button1.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent evt) { 
        Button1_ActionPerformed(evt);
      }
    });
    cp.add(Button1);
    
    setVisible(true);
  } 
  
  public static void main(String[] args) {
    new Fangmich();
  }
  
  public void Button1_ActionPerformed(ActionEvent evt) {
    int maxX = getContentPane().getWidth() - Button1.getWidth();
    int maxY = getContentPane().getHeight() - Button1.getHeight();
    int xLocation = random.nextInt(maxX);
    int yLocation = random.nextInt(maxY);
    Button1.setLocation(xLocation, yLocation);
  } 
}

内容的提问来源于stack exchange，提问作者SlothOath