Layout Managers
§ When in any container like Japplet or
Jframe contains more number of components, it is important to arrange all
components in an attractive way.
§ To make it easy layout manager can be used.
§ A layout manager is an object that controls
the size and position of components inside the container.
§ For example a window is a container that
includes components such as buttons and labels. The layout manager that you
assign to the window determines how the components are sized and positioned
within the window.
§ Layout managers are interface classes.
§ Each layout manager defines methods that
arrange components within a container, and each component within container you
place can be container.
§ So it is possible to write container within
container.
Layout options
§ BorderLayout
§ BoxLayout
§ CardLayout
§ FlowLayout
§ GridBagLayout
§ GridLayout
Border Layout
§ Every content pane is initialized to use
a BorderLayout.
§ Border layout is the default manager class
for all content pane.
§ A
BorderLayout places components in up to five areas: top, bottom, left,
right, and center.
§ All
extra space is placed in the center area.
§ The border layout class provides five named
constants for the regions – BorderLayout.NORTH,.SOUTH,.EAST,.WEST,.CENTER
§ When you place exactly five components in a
container and use borderlayout, each components fills one entire region when
the application runs.
§ Java determines the exact size of each components
based on the components contents.
§ If you drag the container’s border to make
it wider the north, south and center regions become wider, but the east and
west regions do not change.
§ If you increase the containers’ height the
east and west, center region becomes taller, but the north and south regions do
not change.
§ When you create Container name con, you can
set its layout manager to BorderLayout with the following:
§ Con.setLayout(new BorderLayout());
§ Or in Japplet you can write the following:
§ setLayout(new BorderLayout());
§ This.setLayout(new BorderLayout());
import
javax.swing.*;
import java.awt.*;
/*<object
code=bl.class width=200 height=200></object> */
public class bl
extends JApplet
{
Container con= getContentPane();
JButton b1=new JButton("north");
JButton b2=new
JButton("south");
JButton b3=new
JButton("east");
JButton b4=new
JButton("west");
JButton b5=new
JButton("center");
public void init()
{
con.setLayout(new
BorderLayout());
con.add(b1,
BorderLayout.NORTH);
con.add(b2,
BorderLayout.SOUTH);
con.add(b3,
BorderLayout.EAST);
con.add(b4,
BorderLayout.WEST);
con.add(b5,
BorderLayout.CENTER);
}
}
Flow Layout
§ The Flow Layout class puts
components in a row, sized at their preferred size.
§ If the horizontal space in the container is
too small to put all the components in one row, the FlowLayout class uses
multiple rows.
§ If
the container is wider than necessary for a row of components, the row is, by
default, centered horizontally within the container.
§ To specify that the row is to aligned
either to the left or right, use a FlowLayout constructor that takes
an alignment argument.
§ Another constructor of
the FlowLayout class specifies how much vertical or horizontal
padding is put around the components.
§ When you use borderlayout and then resize
the window, the components change size accordingly because their regions
change.
§ When you use BorderLayout and then resize
the window, the components change size accordingly because their region change.
§ When you use flowlayout and then resize the
window, each component retains its size, but it might become partially changed.
§ The flowlayout class contains three
constants you can use to align components with a container:
§ FlowLayout.LEFT
§ FlowLayout.CENTER
§ FlowLayout.RIGHT
import
javax.swing.*;
import java.awt.*;
/*<object
code=fl.class width=200 height=200></object> */
public class fl
extends JApplet
{
Container con= getContentPane();
JButton b1=new JButton("north");
JButton b2=new
JButton("south");
JButton b3=new
JButton("east");
JButton b4=new
JButton("west");
JButton b5=new
JButton("center");
public void init()
{
con.setLayout(new
FlowLayout());
con.add(b1);
con.add(b2);
con.add(b3);
con.add(b4);
con.add(b5);
}
}
GridLayout
§ If you want to use components into equal
rows and columns, you can use the GridLayout manager class.
§ When you create a GridLayout object, you
indicate the number of rows and columns you want, and then the container
surface is divided into a grid, much like a screen you see when using a
spreadsheet program.
§ Con.setLayout(new GridLayout(4,5)) will set
the anonymous grid layout with four horizontal line and 5 vertical line.
§ Similarly, within Japplet you can establish
the same layout with either the following:
§ This.setLayout(new GridLayout(4,5));
§ setLayout(new GridLayout(4,5))
import
javax.swing.*;
import java.awt.*;
/*<object
code=gl.class width=200 height=200></object> */
public class gl
extends JApplet
{
Container con= getContentPane();
JButton b1=new JButton("north");
JButton b2=new
JButton("south");
JButton b3=new
JButton("east");
JButton b4=new
JButton("west");
JButton b5=new
JButton("center");
public void init()
{
con.setLayout(new
GridLayout(2,3,5,5));
con.add(b1);
con.add(b2);
con.add(b3);
con.add(b4);
con.add(b5);
}
}
Card Layout
§ each component that a CardLayout manages is
like a playing card or trading card in a stack, where only the top card is
visible at any time. You can choose the card that is showing in any of the
following ways:
§ By asking for either the first or last
card, in the order it was added to the container
§ By flipping through the deck backwards or
forwards
§ By specifying a card with a specific name
§ CardLayout() A card layout is created from
the card layout without a horizontal or vartical gap.
§ CardLayout(int hgap, int vgap) creates a
card layout with the horizontal and vertical gaps.
import
javax.swing.*;
import java.awt.*;
import java.awt.event.*;
/*<object
code=cl.class width=200 height=200></object> */
public class cl
extends JApplet implements ActionListener
{
Container con= getContentPane();
CardLayout cards =
new CardLayout();
JButton b1=new JButton("north");
JButton b2=new
JButton("south");
JButton b3=new
JButton("east");
public void init()
{
setLayout(cards);
con.add("
",b1);
b1.addActionListener(this);
con.add("
",b2);
b2.addActionListener(this);
con.add("
",b3);
b3.addActionListener(this);
}
public void actionPerformed(ActionEvent
e)
{
cards.next(getContentPane());
}
}
