📄 smalltree.java
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import java.awt.*;
import java.applet.*;
import java.awt.event.*;
class MyCanvas extends Canvas
{
int num,i,px,py;
MyCanvas()
{
setSize(600,600);
setBackground(Color.green);
}
public void setNum(int num)
{
this.num=0;
}
public void setI(int i)
{
this.i=i;
}
public boolean mouseDown(Event evt,int x,int y)//鼠标按下事件
{//Pnum=Integer.valueOf(InPnum.getText()).intValue();
if(num<i){
px=x;
py=y;//鼠标按下时的坐标
num++;//计数器加1
repaint();//重画窗口
}
return true;//返回true,表示事件处理过了
}
public void update(Graphics g)//屏幕刷新时不擦除前点
{
g.setColor(getBackground());//以背景色取出一块区域
//g.fillRect(100*i,100,150,60);
paint(g);//调用paint方法
}
public void paint(Graphics g){
g.setColor(Color.red);
g.fillOval(px,py,10,10);
g.drawString("P"+num,px,py);
}
}
public class SmallTree extends Applet implements ActionListener
{
MyCanvas canvas;
Label l1;
Button b1;
TextField t1,t2;
String s;
int i,px,py;
//int num=0;
public void init()
{
canvas = new MyCanvas();
l1=new Label("请输入点数:");
b1=new Button("确定");
b1.addActionListener(this);
t1=new TextField(4);
t2=new TextField(6);
add(l1);
add(t1);
add(b1);
add(t2);
add(canvas);
}
public void actionPerformed(ActionEvent e)
{
int i;
String s;
try
{
s=t1.getText();
t2.setText(s);
i=Integer.parseInt(s);
canvas.setI(i);
canvas.repaint();
}
catch(NumberFormatException ee)
{i=0;
t2.setText("输入有误!");
}
}
}
/*<html>
<head>
<title>最小生成树</title>
</head>
<body>
<applet code="e2.class"width=1024 height=768></applet>
</body>
</html>*/
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