java布局管理器，不是默认为FlowLayout()吗，怎么只有一个按钮？

import java.awt.*;
public class FlowAp extends Frame{
public static void main(String argv[]){
FlowAp fa=new FlowAp();
fa.setSize(400,300);
fa.setVisible(true);

}

FlowAp(){
add(new Button("One"));
add(new Button("Two"));
add(new Button("Three"));
add(new Button("Four"));
}//End of constructor
}//End of Application