java - 从另一个类访问变量

Question

很简单的问题，但我做不到。我有 3 节课:

DrawCircle 类

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

class DrawCircle extends JPanel
{
    private int w, h, di, diBig, diSmall, maxRad, xSq, ySq, xPoint, yPoint;
    public DrawFrame d;

    public DrawCircle()
    {
        w = 400;
        h = 400;
        diBig = 300;
        diSmall = 10;
        maxRad = (diBig/2) - diSmall;
        xSq = 50;
        ySq = 50;
        xPoint = 200;
        yPoint = 200;
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.setColor(Color.blue);
        g.drawOval(xSq, ySq, diBig, diBig);

        for(int y=ySq; y<ySq+diBig; y=y+diSmall*2)
        {
            for(int x=xSq; x<w-xSq; x=x+diSmall)
            {
                if(Math.sqrt(Math.pow(yPoint-y,2) + Math.pow(xPoint-x, 2))<= maxRad)
                    {
                        g.drawOval(x, y, diSmall, diSmall);
                    }               
            }
        }

        for(int y=ySq+10; y<ySq+diBig; y=y+diSmall*2)
        {
            for(int x=xSq+5; x<w-xSq; x=x+diSmall)
            {
                if(Math.sqrt(Math.pow(yPoint-y,2) + Math.pow(xPoint-x, 2))<= maxRad)
                {
                    g.drawOval(x, y, diSmall, diSmall);
                }   
            }
        }
    }
}

DrawFrame 类

public class DrawFrame extends JFrame
{
    public DrawFrame()
    {
        int width = 400;
        int height = 400;

        setTitle("Frame");
        setSize(width, height);

        addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent e)
            {
                System.exit(0);
            }
        });

        Container contentPane = getContentPane();
        contentPane.add(new DrawCircle());
    }
}

CircMain 类

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

public class CircMain 
{
    public static void main(String[] args)
    {
        JFrame frame = new DrawFrame();
        frame.show();
    }
}

一个类创建一个框架，另一个类绘制一个圆圈并用较小的圆圈填充它。在 DrawFrame 我设置宽度和高度。在 DrawCircle 中，我需要访问 DrawFrame 的宽度和高度。我该怎么做？

我尝试制作一个对象并尝试使用 .getWidth 和 .getHeight 但无法让它工作。我在这里需要特定的代码，因为我尝试了很多东西但无法让它工作。我是否在 DrawFrame 中声明宽度和高度错误？在 DrawCircle 中以错误的方式创建对象吗？

另外，我在 DrawCircle 中使用的变量，我是否应该将它们放在构造函数中？

Answer 1

您可以将变量设为公共(public)字段:

  public int width;
  public int height;

  DrawFrame() {
    this.width = 400;
    this.height = 400;
  }

然后您可以像这样访问变量:

DrawFrame frame = new DrawFrame();
int theWidth = frame.width;
int theHeight = frame.height;

然而，更好的解决方案是让变量私有(private)字段向您的类添加两个访问器方法，从而封装 DrawFrame 类中的数据:

 private int width;
 private int height;

 DrawFrame() {
    this.width = 400;
    this.height = 400;
 }

  public int getWidth() {
     return this.width;
  }

  public int getHeight() {
     return this.height;
  }

然后你可以像这样得到宽度/高度:

  DrawFrame frame = new DrawFrame();
  int theWidth = frame.getWidth();
  int theHeight = frame.getHeight();

我强烈建议你使用后一种方法。