[英]Access variables from class to class
How do i access some variables from another class? 我如何从另一个类访问一些变量? For example, i have 2 files: 例如,我有2个文件:
Main.java 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 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)
{
}
}
}
What do i want is that from KeyThread.java to be able to modify/increment/access values from Main.java especially 我想要的是KeyThread.java中的功能, 尤其是能够修改/增加/访问Main.java中的值
int ballX = 20;
int ballY = 20;
so i can call my thread from Main.java like 所以我可以像这样从Main.java调用我的线程
Thread t5 = new Thread(new KeyThread("Moving Right", ballX = ballX + 1, 20));
t5.start();
How can i do that? 我怎样才能做到这一点? And why is it so hard to do it? 为什么要做那么难?
If you declare your variables public
instead of private
, you can refer to them as (for example) Main.ballX
, but this is generally a bad practice. 如果将变量声明为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。 We organize things into classes to keep separate things separate; 我们将事物组织成类,以使单独的事物保持独立; if we start using the members of class A within class B, then class B has a dependency on A that can make it hard to debug and maintain later on. 如果我们开始在类B中使用类A的成员,则类B对A具有依赖性,这会使以后很难调试和维护。 Better would be to provide a "getter" or "accessor" method inside Main (eg getBallX()
and setBallX(int x)
) which give the owning class (in this case, Main) better control over its private members. 最好在Main内部提供一个“ getter”或“ accessor”方法(例如getBallX()
和setBallX(int x)
),以使拥有类(在这种情况下为Main)更好地控制其私有成员。
另外,将其他答案添加到其他内容中,如果频繁执行的任务似乎是在向值添加/减去值,那么诸如adjustBallX(int x)之类的方法可能会很有价值,因此您可以在不增加值的情况下增加/减少值每次调用get()和set()。
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