java如何将击键Z添加到按键(KeyEvent e)以将球跳跃/重新绘制到新的随机位置?(使用了KeyListener演示。)
我的Java经验有限,尤其是在图形方面。到目前为止,我在这个问题上得到了很大的帮助。这是我在Eclipse中测试的启动代码(位于底部),运行良好。我用它来教一个高中生。根据下面注释中的说明,有人知道一种简单的方法来扩展已经很简单的程序,使球在按下Z按钮后跳跃/移动/重新绘制到一个随机的新位置吗?我正在考虑向按键(KeyEvent e)方法添加以下代码:
else if(keyCode == KeyEvent.VK_Z)
{
//Not sure what to add here. Just want to change X and Y coordinates to
//anything, so long as the program works and stays fairly simple
//for now.
//----> g.fillOval(x + radius, y + radius, 2 * radius, 2 * radius);
// this line above says "g can not be resolved".
}
如果您有任何建议或想法可以使程序简单,我们将不胜感激。谢谢大家!
import java.awt.*;
import java.awt.event.*; // #1
import javax.swing.*;
/******************************************************************************
*
* KeyListenerDemo.java
* Demonstrates getting keyboard input using the KeyListener interface.
*
* Program 18: Extend this program by adding a few more keystroke commands:
* z (VK_Z) - Cause the ball to jump to a random new location.
* s (VK_S) - Make the ball smaller - multiply its diameter 1/2.
* b (VK_B) - Make the ball bigger - multiply its diameter by 2.
* c (VK_C) - Change the color (in any way you'd like).
*
* In addition, modify the program to ensure the following:
* - The ball goes all the way to the edge of the screen but stays
* completely on the screen.
* - If a doubled diameter doesn't fit, make it as large as possible.
* - Be sure the ball never completely disappears.
*
*****************************************************************************/
public class KeyListenerDemo extends JFrame
implements KeyListener // #2
{
// Class Scope Finals
private static final int SCREEN_WIDTH = 1000;
private static final int SCREEN_HEIGHT = 800;
private static final int START_RADIUS = 25;
private static final int START_X = 100;
private static final int START_Y = 100;
private static final int STEP_SIZE = 10;
// Class Scope Variables
private static int x = START_X; // x at center of the ball
private static int y = START_Y; // y at center of the ball
private static int radius = START_RADIUS; // radius of the ball
// Methods
/**
* Create the window and register this as a KeyListener
*
* @param args
*/
public static void main (String[] args)
{
// Set up the JFrame window.
KeyListenerDemo gp = new KeyListenerDemo();
gp.setSize(SCREEN_WIDTH, SCREEN_HEIGHT);
gp.setVisible(true);
gp.addKeyListener(gp); // #3
// If this class had a constructor and you moved this line into
// that constructor it could not refer to gp since that variable
// is local to this method. Instead you would write::
// addKeyListener(this);
}
/**
* Called when a key is first pressed
* Required for any KeyListener
*
* @param e Contains info about the key pressed
*/
public void keyPressed(KeyEvent e) // #4A
{
int keyCode = e.getKeyCode();
if (keyCode == KeyEvent.VK_LEFT)
{
x = x - STEP_SIZE;
}
else if (keyCode == KeyEvent.VK_RIGHT)
{
x = x + STEP_SIZE;
}
else if (keyCode == KeyEvent.VK_UP)
{
y = y - STEP_SIZE;
}
else if (keyCode == KeyEvent.VK_DOWN)
{
y = y + STEP_SIZE;
}
repaint();
}
/**
* Called when typing of a key is completed
* Required for any KeyListener
*
* @param e Contains info about the key typed
*/
public void keyTyped(KeyEvent e) // #4B
{
}
/**
* Called when a key is released
* Required for any KeyListener
*
* @param e Contains info about the key released
*/
public void keyReleased(KeyEvent e) // #4C
{
}
/**
* paint - draw the figure
*
* @param g Graphics object to draw in
*/
public void paint(Graphics g)
{
g.setColor(Color.white);
g.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
g.setColor(Color.blue);
g.fillOval(x - radius, y - radius, 2 * radius, 2 * radius);
}
}
# 1 楼答案
无法解析
g
的原因是keyPressed()
方法中不存在它g
是方法paint()
的一个参数。这意味着您只能在方法paint()
中引用它。您可以在方法paint()
之外声明另一个名为g
的变量,但它不会是相同的g
。它甚至不需要有相同的类型也就是说,你根本不需要直接引用
g
来解决你的问题。paint()
方法已经可以处理绘制圆。你只需要改变圆圈的位置,并告诉应用程序重新绘制它。如果给x
和y
分配新值,然后调用repaint()
,圆圈将移动。注意repaint()
已经在keyPressed()
方法的末尾被调用下面是一个例子。用任何适合您的问题的代码替换equals右边的代码
如果你看看其他的If/else条款,你会发现这也是他们正在做的事情
# 2 楼答案
尝试这样做:
然后
希望这有帮助