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Why the button doesn't appears in the Frame?

 
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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();
}
}
When I compile and run the code above , but no component is visible,Why?
 
Greenhorn
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Originally posted by Gong James:
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();
}
}
When I compile and run the code above , but no component is visible,Why?


Can u please delete or comment the following line
setLayout(new BorderLayout());
and then try.

 
Gong James
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Of course you are right,but you mistaked my meaning.
you know java allow you to change the layoutmanager,when the layoutmanager is changed ,the container will layout the component with it's rule.

Concern this case ,i changed the layoutmanager to flowlayout manager,but the button doesn't appear as my plan.
Why?or What's the rule when layout manager is changed from border layout to flow layout ?
 
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Hi James,
The problem is after line
setLayout(new BorderLayout());
Pay attention to the following rules:
1. Construct the frame.
2. Give the frame a layout manager.
3. Populate the frame (in you code above you omit this step)
...
So now simply add your button after line (means frame is populated with the components)
setLayout(new BorderLayout());
and it'll work.
------------------
Alex J.Grig
[This message has been edited by Alex Grig (edited October 31, 2001).]
 
Alex Grig
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According to the "Complete Java 2 Certification Study Guide" we can summarise "After each container is constructed and assigned an appropriate layout manager, the conteiner is poppulated with the components it is to contain"
------------------
Alex J.Grig
 
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Alex is right, but I'd put this in a different way. BorderLayout implements LayoutManager2, which means that it keeps it's own list of components.
To be more specific, if you added some components to a container and then apply a layout that implements LayoutManager2, this one attempts to redraw the components from own list. But his list is empty because all the components have been added before the layout beeing set.
This is why you don't see anything.
Adrian
 
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raj_sb
Would you kindly read our naming policy and re-register with a proper name?
www.javaranch.com/name.jsp
thanks
 
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