Question

如何从其他类访问某些变量？例如，我有2个文件：

Main.java

package keyboardgame;

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class Main extends Applet implements KeyListener
{

    private static final long serialVersionUID = 1L;
    private static boolean keyboardRightPressed = false;
    private static boolean keyboardLeftPressed = false;
    private static boolean keyboardUpPressed = false;
    private static boolean keyboardDownPressed = false;

    int ballX = 20; 
    int ballY = 20;
    int ballSpeed = 10;

    public void init()
    {
        addKeyListener(this);
    }

    public void keyPressed(KeyEvent e) 
    {
        int keyCode = e.getKeyCode();
        if(keyCode == KeyEvent.VK_RIGHT)
        {
            keyboardRightPressed = true;
            ballX = ballX + ballSpeed;
            repaint();
        }

        if(keyCode == KeyEvent.VK_LEFT)
        {
            keyboardLeftPressed = true;
            ballX = ballX - ballSpeed;
            repaint();
        }

        if(keyCode == KeyEvent.VK_UP)
        {
            keyboardUpPressed = true;
            ballY = ballY - ballSpeed;
            repaint();
        }

        if(keyCode == KeyEvent.VK_DOWN)
        {
            keyboardDownPressed = true;
            ballY = ballY + ballSpeed;
            repaint();
        }
    }

    public void keyReleased(KeyEvent e) 
    {
        int keyCode = e.getKeyCode();
        if(keyCode == KeyEvent.VK_RIGHT)
        {
            keyboardRightPressed = false;
            repaint();
        }

        if(keyCode == KeyEvent.VK_LEFT)
        {
            keyboardLeftPressed = false;
            repaint();
        }

        if(keyCode == KeyEvent.VK_UP)
        {
            keyboardUpPressed = false;
            repaint();
        }

        if(keyCode == KeyEvent.VK_DOWN)
        {
            keyboardDownPressed = false;
            repaint();
        }
    }

    public void keyTyped(KeyEvent e) {
    }


    public void paint(Graphics g)
    {
        g.fillOval(ballX,ballY,20,20);
        g.drawString("Right :"+keyboardRightPressed,0,10);
        g.drawString("Left :"+keyboardLeftPressed,0,20);
        g.drawString("Up :"+keyboardUpPressed,0,30);
        g.drawString("Down :"+keyboardDownPressed,0,40);        
    }

}

KeyThread.java

package keyboardgame;

public class KeyThread implements Runnable
{

    public KeyThread(String s,int speed)
    {
        name = s;
        time = speed;
    }

    public void run() 
    {
        try
        {
            if(keyboardRightPressed == true)
            {
                ballX = ballX + 10; 
                ballY = ballY + 10;
            }
        }
        catch(Exception e)
        {

        }
    }
}

我想要的是 KeyThread.java 能够修改/增加/访问 Main.java 中的值，尤其是

int ballX = 20; 
int ballY = 20;

所以我可以从 Main.java 中调用我的帖子，如

Thread t5 = new Thread(new KeyThread("Moving Right", ballX = ballX + 1, 20));
t5.start();

我该怎么做？为什么这么难呢？

Answer 1

为了调用对象的非静态方法，您需要该类的实例。有关详细信息，请参阅Objects。

Answer 2

如果您声明变量public而不是private，则可以将它们称为（例如）Main.ballX，但这通常是一种不好的做法。我们将事物组织成课程以将各个事物分开;如果我们开始在类B中使用类A的成员，那么类B依赖于A，这可能使以后难以调试和维护。更好的方法是在Main（例如getBallX()和setBallX(int x)）中提供一个“getter”或“accessor”方法，它可以让拥有类（在本例中为Main）更好地控制其私有成员。 / p>

Answer 3

此外，添加到其他答案，如果一个频繁的任务将要添加/减去该值似乎是一个方法，如adjustBallX（int x）可能是有价值的，所以你可以增加/减少每次都不调用get（）和set（）的值。

从类到类的访问变量

3 个答案: