



Flow Layout


The default layout manager used with Applets is FlowLayout. This is also
true for Panels. This is not the case for Windows, Dialogs, and Frames.
They all use something called BorderLayout. 
There are five layout managers used in Java 1.1: FlowLayout, BorderLayout,
GridLayout, GridBag Layout, and CardLayout. You also have the option of
using no layout manager or creating your own layout manager. In this lesson
we will discuss FlowLayout. Subsequent lessons will discuss
 BorderLayout, GridLayout, and using no Layout.

FlowLayout: When you use FlowLayout, components are added
to a container from left to right and top to bottom in the order in which
the add method is called for them in your program. Here's a quick example
to make this clear:


import java.awt.*;
import java.applet.*;

public class quick extends Applet{
  Button b;
  Label l;
  TextField f;
  Checkbox c;
  //Buttons, Labels, TextFields and Checkboxes are 
  //examples of components

  public void init(){
    setBackground(Color.yellow);
    //call constructors for each component
    b=new Button("Fourth");
    l=new Label("First");
    f=new TextField("Second");
    c=new Checkbox("Third");
    //add each component
    add(l);
    add(f);
    add(c);
    add(b);
  }
}





As you can see the applet's add method was called first for the label, then
for the textfield, then for the checkbox, and finally for the button.
They are displayed in the applet in this same order. Now if we change the
dimensions on the applet so that it is less wide, then we get the following
result:


You will note that the components are still in the same order, but some
got shuffled down to the next row since there wasn't room in the first
row!

Constructors: There are three constructors used by the FlowLayout
class:
1. FlowLayout(): This is the default constructor. By default the spacing
between components is set to a gap of five pixels in both the horizontal
and vertical directions. Also the default alignment used for the components
is center (FlowLayout.CENTER).

2. FlowLayout(int align): This constructor maintains default spacing, but
allows the user to specifiy alignment. The choices are FlowLayout.CENTER,
FlowLayout.LEFT, and FlowLayout.RIGHT.

3. FlowLayout(int align, int hori, int vert): This constructor allows control
of spacing and alignment. Spacing is in terms of pixels.

FlowLayout Methods: There are three interesting looking layout
methods:
1. setAlignment(int align): This allows you to modify alignment.

2. setHgap(int hori): This allows you to change the horizontal spacing between
components.

3. setVgap(): This allows you to change the vertical spacing between
components.

In order to use them you have to declare an instance of FlowLayout.
Normally you could just write:

      setLayout(new FlowLayout());

But if you want to use a FlowLayout method you have to:

      FlowLayout f = new FlowLayout();

      setLayout(f);

Here's an example which uses the
FlowLayout methods:


import java.awt.*;
import java.applet.*;

public class exp extends Applet{
  //The following line declares an array of Buttons.
  //Don't worry about arrays just yet.

  Button[] b= new Button[20];

  public void init(){
    FlowLayout f = new FlowLayout();
    setBackground(Color.cyan);
    setLayout(f);
    f.setAlignment(FlowLayout.RIGHT);
    f.setHgap(30);
    f.setVgap(30);
    //The following line begins a for-loop.
    //Don't worry about this just yet.
    for(int i=0; i<b.length; i++){
      b[i]=new Button("Button"+(i+1));
      b[i].setBackground(Color.yellow);
      add(b[i]);
    }
  }
}

//<applet code=exp.class height=250 width=600></applet>









Assignment: You will create an applet which contains 
nine buttons. Each button will have the name of some food on it. At the 
bottom of your applet you will have the words: "Pick your favorite".
You will use drawString to do this in the paint method. You will size
your applet so that the nine buttons line up in three rows of three. You
will then make sure you have enough space left over at the bottom of your
applet area for the "Pick your favorite" string. This will take some
experimentation and adjustments, but it is not a hard assignment.