从另一个类访问变量 [英] accessing a variable from another class

问题描述

非常简单的问题，但我不能这样做。我有3个班级：

Very simple question but I can't do it. I have 3 classes:

DrawCircle class

DrawCircle class

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 class

DrawFrame class

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 class

CircMain class

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 中设置宽度和高度。在 DrawCircle 中，我需要访问 DrawFrame 的宽度和高度。我该怎么做？

One class creates a frame, the other draws a circle and fills it with smaller circles. In DrawFrame I set width and height. In DrawCircle I need to access the width and height of DrawFrame. How do I do this?

我试过制作一个对象并尝试使用 .getWidth 和 .getHeight 但无法让它工作。我需要特定的代码，因为我已经尝试了很多东西，但无法让它工作。我是否在 DrawFrame 中声明宽度和高度错误？我在 DrawCircle 中错误地创建对象？

I've tried making an object and tried using .getWidth and .getHeight but can't get it to work. I need specific code here because I've tried a lot of things but can't get it to work. Am I declaring width and height wrong in DrawFrame? Am creating the object the wrong way in DrawCircle?

此外，我在 DrawCircle ，我是否应该在构造函数中使用它们？

Also, the variables i use in DrawCircle, should I have them in the constructor or not?

推荐答案

你可以制作变量公共字段：

You could make the variables public fields:

  public int width;
  public int height;

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

然后你可以像这样访问变量：

You could then access the variables like so:

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

然而，更好的解决方案是使变量私有字段为您的类添加两个访问器方法，保持DrawFrame类中的数据封装：

A better solution, however, would be to make the variables private fields add two accessor methods to your class, keeping the data in the DrawFrame class encapsulated:

 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：

Then you can get the width/height like so:

  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。

I strongly suggest you use the latter method.

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