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[英]How do I add keystroke Z to keyPressed(KeyEvent e) to jump/repaint the ball to a new random location? (KeyListener demo used.)
[英]How do I add a keystroke inside of keyPressed(KeyEvent e) method to change color of ball? simple KeyListener demo
我對Java的經驗有限,尤其是與圖形有關的經驗。 到目前為止,我已經在這個問題上提供了很好的幫助。 當我在Eclipse中對其進行測試時,它的啟動代碼(如下)可以正常工作。 我正在課堂上使用它來教一名高中生。 按照下面注釋中的說明,有人會知道一種簡單的方法來擴展已經很簡單的程序,以在按下按鈕C后更改球的顏色嗎? 我正在考慮將以下代碼添加到keyPressed(KeyEvent e)方法中:
else if(keyCode == KeyEvent.VK_C)
{
//Not sure what code to add here
//g.setColor(Color.green); ----> this line says "g can not be resolved".
}
任何使程序簡單的技巧或想法將不勝感激。 謝謝。 。
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);
}
}
private Color currentColor;
...
public void paint(Graphics g)
{
g.setColor(Color.white);
g.fillRect(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);
g.setColor(currrentColor);
g.fillOval(x - radius, y - radius, 2 * radius, 2 * radius);
}
...
public void keyPressed(KeyEvent e)
{
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;
}else currentColor = Color.BLUE;
repaint();
}
您可能應該這樣做。
您在按鍵事件中沒有'g'圖形變量,因此您從編譯器中得到未解決的變量錯誤。 需要存儲顏色以繪制變量並在paint方法中使用它。
有一個是顏色的類實例變量。 最初是
colorBall = Color.white
然后單擊C(如果其白色變為綠色),反之亦然。
在繪畫中,只需使用變量即可上色
g.setColor(colorBall );
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