本题的功能是定义自己的组件类。窗口中排布着12个按钮，鼠标移动按钮时，按钮背景颜色改变，用鼠标单击按钮时，后台将显示该按钮对应的字符。
import java.awt.*;
import java.awt.event.*;
import java.util.*;
class java3 extends Frame
String keys="123456789*0#";
java3()
super("java3");
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System.exit(0);
);

setLayout(new GridLayout(4,3,6,6));
for(int i=0;i＜keyslength;i++))
KeyButton kb=new KeyButton(keys.charAt(i));
kb.addkeyListener(this);
kb.setBackground(C010r.pink);
kb.setForeground(Color.black);
add(kb);

setSize(200,200);
show();

class KeyEVentHandler extends KeyAdapter
public void keyTyped(KeyEvent evt)
System.out.println(evt,getChar());


public static void main(String[]args)
new java3();


class KeyButton extends Component
KeyListener keyListener;
boolean highlighted;
char key;
KeyButton(char k)
this.key=k;
addMouseListener(new MouseEventHandler());

public void paint(Graphics g)
int w=getSize().width;
int h=getSize().height;
String s=""+key;
FontMetrics fm=g.getFontMetrics();
if(highlighted)
g.setColor(getBackground());
g.fillRoundRect(0,0,w-1,h-1,10,10);

g.setColor(getForeground());
g.drawR0undRect(O，0，w一1，h一1，10，10)：
g.drawString(s,(w-fm.stringWidth(s))/2,
(h-fm.getHeight())/2+fm.getAscent());

class MouseEventHandler extends MouseAdapter
public void mousePressed(MouseEvent evt)
if(keyListener!=null)
keyListener.keyTyped
new KeyEvent(KeyButton.this,KeyEvent.KEYTYPED,
System.currentTimeMillis(),
0,KeyEvent.VK_UNDEFINED,key));


public void mouseEntered(MouseEvent evt)
highlighted=true;
repaint();

public void mouseExited(MouseEvent evt)
highlighted=false;
repaint();


public synchronized void addKeyListener(KeyLis-tener 1)
keyListener=AWTEventMulticaster.add(key-Listener,1)；

public synchronized void removeKeyListener(Key-Listener 1)
keyLstener=AWTEventMulticaster.remove
(keyListener,1);

按形成以后至勘察前后有无变化，刑事犯罪现场可分为( )。

A．主体现场和关联现场
B．原始现场和变动现场
C．真实现场和伪造现场
D．第一现场和第二现场