awt problem

[payal sharma]

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(); 
      } 
 }

it compile and run but nothing is visible
but
this one is visible

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 BorderLayout()); 
       add(bSouth,BorderLayout.SOUTH); 
       add(bWest,BorderLayout.WEST); 
       add(bEast,BorderLayout.EAST); 
       add(bNorth,BorderLayout.NORTH); 
       add(bCenter); 
       setLayout(new FlowLayout()); 
       validate(); 
       pack(); 
       setVisible(true); 
  } 
  public static void main(String args[]) 
  { 
       TestFrame tf = new TestFrame(); 
  }
 }

Now in grid layout

import java.awt.*; 
 public class TestFrame extends Frame 
 { 
      public TestFrame() 
      { 
           setLayout(new GridLayout(2,1)); 
           for(int i = 1 ; i <= 4 ;++i) 
           { 
               add(new Button(Integer.toString(i))); 
           } 
           pack(); 
           setVisible(true); 
      } 
      public static void main(String args[]) 
      { 
           TestFrame tf = new TestFrame(); 
      } 
 }

it has to be two row and one column but showing 2 x 2 matrix why?

[Manfred Leonhardt]

Hi Payal,
In your first two codes you are running into the difference between LayoutManager and LayoutManager2. The containers that implement LayoutManager2 require constraints to be supplied in order to perform the layout.
In your first code example, you have not supplied any constraints while adding your components, which is not required by FlowLayout. Then you switch your layout to BorderLayout and the layout doesn't have any constraints for the components. Therefore you see no components being layed out!
In your second code example you are doing the opposite. In that case the FlowLayout just ignores your constraints and doesn't its own layout.
Your last question regarding GridLayout. The reason for the name is that the entire contents is divided up into equal sized grids. There will always be the number of rows and cols that you specify in the creation. There are specific rules on what will happen if you add more components then you have grids. Please see the API documentation for that explanation. NOTE: GridBagLayout will allow you to have any number of grids of any size in a layout!
Regards,
Manfred.

[tvs sundaram]

RHE says that the Grid Layout will behave unpredictably when we add more or less components than the no of cells created.
Is it anything to do with that..
comments pls..

[tvs sundaram]

For your first question it is about new layout querying the previous layout regarding the components added to it.
The layouts implementing Layoutmanager will query the previous layout. i.e flow, Grid
layouts implementing LayoutManager2 will not query the previous layout manager regarding the components added. They will start afresh in the screen and will add components only after that. i.e,border, card, gridbag
With this reasoning if u analyse your question the answer will be clear.
HTH
any comments/ corrections welcome.