layout mock question

[mark stone]

import java.awt.*;
public class TestFrame extends Frame
{
Button bNorth = new Button("North");
Button bSouth = new Button("South");
Button bEast = new Button("East");
Button bWest = new Button("West");
Button bCenter = new Button("Center");
public TestFrame()
{
setLayout(new FlowLayout());
add(bNorth);
add(bSouth);
add(bWest);
add(bEast);
add(bCenter);
setLayout(new BorderLayout());
validate();
setSize(300,300);
setVisible(true);
}
public static void main(String args[])
{
TestFrame tf = new TestFrame();
}
}
in this question the layout is set to be Flow and then components are added. and then layout is changed to Border. but BorderLayout needs that components be specifically allotted to their 5 respective positions, which if not, nothing is visible. Hence nothing is visible. is the reasoning correct ?

[Roy Ben Ami]

your reasoning is half correct.
in this case u r right. because it is at fist flowLayout and then u add the components and u change to borderLayout then the LayoutManeger doesnt know how to validate the components (which one should he put where) so he doesnt show anything.
BUT , u dont have to specify always for BorderLayout where to put everything.
for example:
setLayout(new BorderLayout());
add(new Button("cool"));
this code will work and will put by "default" the button in the center.
any more items will be instead of this one at the center.