java中 JOptionPane.showMessageDialog()总是出现错误,请高手指教,谢谢
import javax.swing.JOptionPane;
class Circle
{
double Radius;
void setRadius(double Radius)/*返回半
径*/
{
this.Radius=Radius;
}
void showRadius()
{
System.out.println("radius is :"+Radius);
}
double showArea(){ //计算面积
return Math.PI*Math.pow(Radius,2);
}
}
class b{
public static void main(String []args)
{
Circle acircle =new Circle ();
String str=JOptionPane.showInputDialog("请输入半径");
double d=Double.parseDouble(str);
acircle.setRadius( d);
double j=acircle.showArea();
System.out.println("面积是:"+j);
JOptionPane.showMessageDialog(null,j,"Finish",JOptionPane.INFORMATION_MESSAGE);
System.exit(0);
}
}
上面的程序代码出现了以下的错误:
D:\java>javac a.java
a.java:6: cannot resolve symbol
symbol : method showMessageDialog (<nulltype>,int,java.lang.String,int)
location: class javax.swing.JOptionPane
JOptionPane.showMessageDialog(null,1,"1",JOptionPane.INFORMATION_MESSAGE);
^
1 error