Transcript TCU CoSc 10403 Programming with Java

TCU CoSc 10403
Programming with Java
Visual Design
(Chapter 5)
Containers & Layout Managers
• Java provides two features that give us the ability to
make a GUI look the way we want it to, regardless of
the system in which the program is running.
• Layout classes allow the programmer to specify how
the hierarchy of Containers and their components
will appear to the user.
• The Container subclass permits the programmer to
think of visual design as a hierarchical organization.
Arranging components
• Every Container has a layout manager
– You do not directly control where components are placed; the layout
manager does this for you
• The default layout for a Panel or JPanel is FlowLayout
• The default layout for a JApplet is BorderLayout
• You can set the layout manager explicitly; for example,
– setLayout(new FlowLayout());
– setLayout(new BorderLayout());
or
– FlowLayout lo = new FlowLayout();
setLayout(lo);
3
Containers
• Container objects are used to group Components (widgets)
together for display purposes.
• There is no limit to the number of Components that a
Container can hold.
• A Container is itself a component - can be nested!
Component
Container
Panel
Applet
JApplet
Window
FlowLayout
• Use:
add(component);
to add a component when using a FlowLayout
• Components are added left-to-right
• If no room, a new row is started
• Exact layout depends on size of Applet/JApplet
• Components are made as small as possible
• FlowLayout is convenient but often provides little control over the
placement of components within a container.
5
The FlowLayout Class
Constructors:
(1) FlowLayout()
Creates a FlowLayout object with center alignment and horizontal
and vertical gaps of five pixel each. This is the default Layout
Manager for Applets, Panels, and JPanels (not for JApplets!!).
(2) FlowLayout(int alignment)
Constructs a FlowLayout object with the specified alignment and a
default gap of five pixels in each direction.
(3) FlowLayout(int alignment, int hGap, int vGap)
Constructs a FlowLayout object with the specified alignment and
gaps
FlowLayout Example
import java.awt.*;
import javax.swing.*;
public class FlowLayoutDemo extends
JApplet
{
JButton b1 = new JButton("Front");
JButton b2 = new JButton("Left");
JButton b3 = new JButton("Top");
JButton b4 = new JButton("Back");
JButton b5 = new JButton("Right");
JButton b6 = new JButton("Bottom");
public void init()
{
setLayout(new FlowLayout());
add(b1);
add(b2);
add(b3);
add(b4);
add(b5);
add(b6);
}
}
FlowLayout Manager (centered, 5,5);
FlowLayout myLO =
new FlowLayout(FlowLayout.LEFT,20,2);
setLayout(myLO);
FlowLayout myLO =
new FlowLayout(FlowLayout.RIGHT,20,5);
setLayout(myLO);
The BorderLayout Class
•
In a BorderLayout, the Container is divided into five regions: North, East, West, South,
and Center.
North
West
Center
East
South
•
At most five components can be added.
•
To add Component(s) to a Container that has a BorderLayout, we MUST use the
version of the add() method that takes an additional String argument:
void add(String location, Component c)
•
The location is specified using one of the five class constants:
BorderLayout.WEST (“West”), BorderLayout.EAST (“East”),
BorderLayout.SOUTH (“South”), BorderLayout.NORTH
(“North”), and BorderLayout.CENTER (“Center”)
The BorderLayout Class (continued)
• Component(s) do not have to be added to each region – any missing ones will be
treated as Component(s) of size 0.
•
Horizontal and vertical gaps between regions can be specified (the default is 0 unless
specified).
•
When the Container is laid out, the North and South Component(s) are given
their full heights and any remaining vertical space is allotted to the East, Center,
and West regions. In addition, these two Component(s) are given the full
Container width.
•
In the horizontal direction, the East and West regions are given their full widths
and any remaining width is given to the Center region.
• BorderLayout will automatically resize the Component(s) (particularly in the
Center) to fill the available space.
•
To prevent resizing during layout, Component(s) can be placed in Panel(s) or
JPanel(s), and then the Panel(s)/JPanel(s) can be added to the
Container.
The BorderLayout Class
Constructors:
(1) BorderLayout()
Creates a BorderLayout object with center alignment and horizontal
and vertical gaps of zero pixels each.
(2) BorderLayout(int hGap, int vGap)
Constructs a BorderLayout object with center alignment and the
specified alignment and gaps
BorderLayout Example
import java.awt.*;
import javax.swing.*;
public class BorderLayoutDemo extends JApplet
{
BorderLayout myLO = new BorderLayout();
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()
{
setLayout(myLO);
add(BorderLayout.NORTH,b1);
add("South",b2);
add(BorderLayout.EAST,b3);
add("West",b4);
add(BorderLayout.CENTER,b5);
}
}
BorderLayout Example
import java.awt.*;
import javax.swing.*;
public class
{
JButton b1
JButton b2
JButton b3
JButton b4
JButton b5
BorderLayoutDemo2 extends JApplet
=
=
=
=
=
new
new
new
new
new
JButton("North");
JButton("South");
JButton("East");
JButton("West is the longest button");
JButton("Center");
public void init()
{
setLayout(new BorderLayout());
add("North",b1);
add("South",b2);
add("East",b3);
add("West",b4);
add("Center",b5);
}
}
BorderLayout Example
import java.awt.*;
import javax.swing.*;
public class
{
JButton b1
JButton b2
JButton b4
JButton b5
BorderLayoutDemo2 extends JApplet
=
=
=
=
new
new
new
new
JButton("North");
JButton("South");
Empty “East” region
JButton("West is the longest button");
JButton("Center");
public void init()
{
setLayout(new BorderLayout());
add("North",b1);
add("South",b2);
add("West",b4);
add("Center",b5);
}
}
Empty “East” & “Center” regions
BorderLayout Example
import java.awt.*;
import javax.swing.*;
public class
{
JButton b1
JButton b2
JButton b3
JButton b4
JButton b5
BorderLayoutDemo2 extends JApplet
=
=
=
=
=
new
new
new
new
new
JButton("North");
JButton("South");
JButton("East");
JButton("West is the longest button");
JButton("Center");
public void init()
{
setLayout(new BorderLayout());
add("North",b1);
add("South",b2);
add("East",b3);
add("West",b4);
//add("Center",b5);
}
}
Notice the “hole”?
BorderLayout Example
import java.awt.*;
import javax.swing.*;
public class
{
JButton b1
JButton b2
JButton b3
JButton b4
JButton b5
BorderLayoutDemo1 extends JApplet
=
=
=
=
=
new
new
new
new
new
BorderLayout
is the default.
JButton("North");
JButton("South");
JButton("East");
JButton("West");
JButton("Center");
public void init()
{
//note: BorderLayout is the default - even
//if not specified
//setLayout(new FlowLayout());
add(BorderLayout.NORTH,b1);
add("South",b2);
add(BorderLayout.EAST,b3);
add("West",b4);
add(BorderLayout.CENTER,b5);
}
}
What you will get if you mistakenly write:
setLayout(new FlowLayout());
The GridLayout Class
•
In a GridLayout, the Container is divided into equal sized regions (cells) similar
to the squares on “graph paper”.
•
In this layout scheme, both the number of rows and number of columns are specified.
•
When adding Component(s) to a GridLayout, they are placed in the layout in a left
to right, top down order.
•
Cells are of equal size and are completely filled across before filling of a new row
begins.
•
Obviously, the last row may not be completely filled.
•
If more items are added to the Container than there are cells, the layout will allocate
enough columns to fit all the Component(s).
•
GridLayout will resize the Component(s) so that its cells are filled.
•
The layout allows the user to specify both horizontal and vertical spacing (with a default
size of 0).
The GridLayout Class
Constructors:
1. GridLayout()
Creates a new GridLayout with one row, and unlimited number of
columns, and no horizontal and vertical gaps between cells.
2. GridLayout(int rows, int cols)
Creates a new GridLayout with the number of rows and columns
as specified.
3. GridLayout(int rows, int cols, int
hgap, int vgap)
Creates a new GridLayout with number of rows, columns,
horizontal, and vertical gaps as specified.
import java.awt.*;
import javax.swing.*;
GridLayout Example
public class GridLayoutDemo extends
JApplet
{
JButton b1 = new JButton("One");
JButton b2 = new JButton("Two");
JButton b3 = new JButton("Three");
JButton b4 = new JButton("Four");
JButton b5 = new JButton("Five");
setLayout(new GridLayout(5,1));
public void init()
{
setLayout(new GridLayout(2,3,5,10));
add(b1);
add(b2);
add(b3);
add(b4);
add(b5);
}
setLayout(new GridLayout(2,1));
setLayout(new GridLayout(4,1));
}
Java computes the number of columns needed without
regard to the values provided in the constructor.
Num of cols =
(Num of components + rows specified -1)
rows specified
setLayout(new GridLayout(1,3));
Additional columns automatically allocated to fit all the components.
Container Example
Crate of Jolly Ranchers (lifesavers - assorted)
Watermelon rolls (box)
...
Green Apple rolls (box)
Variety pack rolls(box)
Peach rolls (box)
Roll #1
...
...
Roll #20
...
Watermelon piece1
Roll #1
...
...
Roll #20
Roll #1
...
...
Roll #1
Roll
. . #20
.
Lemon pieces
Peach piece 1
...
Raspberry pieces
Roll
. . #20
.
Rootbeer pieces
Tangerine pieces
Controlling Layouts
•
Component(s) placement on a form are controlled by a layout manager
that decides how the Component(s) lie largely based on the order that
they are add(ed) to the form.
•
The size, shape, and placement of components will differ from one
layout manager to another.
•
Layout managers adapt to the dimensions of your Applet/JApplet or
application window, so if that window dimension is changed the size,
shape, and placement of the components could change.
•
We use Containers to group components into manageable units that
help with their presentation on the screen.
•
An Applet/JApplet is one such container and several others (each with
its own specific purpose) are defined in the Java API.
•
Container(s) are subdivided into those that must be attached to another
graphical surface (e.g., Panel/JPanel and Applet/JApplet) and those that
can be moved independently (Window and its children: Frame and
Dialog).
Keeping Track of Things
•A container knows
–what components are in it (could be other containers)
–It’s own (local) coordinate system
•A component knows
–It’s parent (the container it is in)
• There is no limit to the number of Components a Container can
hold.
• Each Container has its own Layout Manager (of which there are
6 provided in Java (Flow, Border, Grid, GridBag, Card, and Box
– we will only use the first 3!!).
• If a container's default layout manager doesn't suit your needs,
you can easily replace it with another one.
Adding Components to a Container
• void add(Component c)
–Add to the end of a list of components in this container
• void add(Component c, int position)
–Add component at specified position (starting at 0; must be between 0
and current # of components; -1 to add at end)
• void add(String name, Component C)
–Useful with some Layout managers (Border and Card)
• Warning!!!
–If you add a component that has already been placed in another container, it
will be removed from original container
The Containment Hierarchy
• The containment hierarchy is not determined by the order in which you add
Component(s) to a Container, but rather by which ones you add to
which.
• There is no limit to the number of Component(s) a Container may hold.
• Since the Container class is a subclass of Component, a Container
object has access to all the Component methods through inheritance
(we’ve used some of these already : setSize(), setForeground(),
setBackground(etc.).
• Since a Container is itself a Component, we can put Containers
within other Containers.
• By so doing, each Container can have its own LayoutManager that
determines how its Component(s) will be arranged within the
Container when it is displayed. Note: each Container has its own local
coordinate system, measured from the anchor point of its bounding
rectangle.
• The Container class is a large class having around 40 methods.
The JPanel Class
• The Container of choice for arranging Component(s).
• JPanel is a class of Container that is itself contained within a
Container.
• JPanel is a Container that does not create a separate window of its
own.
• It is suitable for holding other Components such as JButton(s),
JComboBox(s), JLabel(s), etc.
• Once a top-level window is defined (implicit in the case of a JApplet),
the JPanel class can be used to divide up the larger area into manageable
sections. Each can have its own Layout Manager.
Constructors:
(1)
The JPanel Class
JPanel()
Builds a JPanel object with default layout manager (FlowLayout).
(2)
JPanel(LayoutManager layout)
Builds a JPanel object with the indicated layout manager.
Methods:
A JPanel has no additional methods of interest to us, beyond those it inherits from
Container, Component, and Object.
• void setLayout(LayoutManager layout)
Allows the user to change the LayoutManager of this Container.
• void doLayout()
Instructs this Container’s LayoutManager to lay out the Component(s). Used to force
layout to take place, rather than waiting for it to be done automatically for you.
• LayoutManager getLayout()
Returns the current LayourManager for this Container.
• Dimension getMinimumSize()
• Dimension getPreferredSize()
Asks the LayoutManager to compute the minimum or perferred sizes, necessary to hold all
of this Container’s Component(s).
FlowLayout Panel Demo
import java.awt.*;
import javax.swing.*;
public class FlowLayoutPanelDemo extends JApplet
{
JButton b1 = new JButton("One");
JButton b2 = new JButton("Two");
JButton b3 = new JButton("Three");
JButton b4 = new JButton("Four");
JButton b5 = new JButton("Five");
JButton b6 = new JButton("Six");
JPanel p = new JPanel(); //defaults to FlowLayout
public void init()
{
setLayout(new FlowLayout());
add(b1);
add(b2);
add(b3);
add(p);
p.add(b4);
p.add(b5);
p.add(b6);
}
}
import java.awt.*;
import javax.swing.*;
Buttons, BorderLayout, & Panels
public class BorderLayoutPanelDemo extends JApplet
{
BorderLayout myLO = new BorderLayout();
JPanel p1 = new JPanel();
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()
{
this.setLayout(myLO);
add("North",b1);
add("South",b2);
add("East",b3);
add("West",b4);
add("Center",p1);
p1.add(b5);
}
}
import java.awt.*;
import javax.swing.*;
BorderLayout Panel Demo
public class BorderLayoutPanelDemo1 extends JApplet
{
JButton b1 = new JButton("One");
JButton b2 = new JButton("Two");
JButton b3 = new JButton("Three");
JButton b4 = new JButton("Four");
JButton b5 = new JButton("Five");
JButton b6 = new JButton("Six");
JButton b7 = new JButton("Seven");
JButton b8 = new JButton("Eight");
JButton b9 = new JButton("Nine");
JPanel p = new JPanel(new BorderLayout());
public void init()
{
setLayout(new FlowLayout());
add(b1);
add(b2);
add(b3);
add(b4);
add(p);
p.add("North",b5);
p.add("West",b6);
p.add("Center",b7);
p.add("East",b8);
p.add("South",b9);
}
}
GridLayout & Panels
import java.awt.*;
import javax.swing.*;
public class
{ JButton b0
JButton b1
JButton b2
JButton b3
ButtonTest extends JApplet
= new JButton ("0");
= new JButton ("1");
= new JButton ("2");
= new JButton ("3");
public void init()
{setLayout(new GridLayout(2,2));
add(b0); add(b1); add(b2); add(b3);
}
}
import java.awt.*;
import javax.swing.*;
public class
{
JButton b0
JButton b1
JButton b2
JButton b3
ButtonTest extends JApplet
=
=
=
=
new
new
new
new
JButton
JButton
JButton
JButton
("0");
("1");
("2");
("3");
JPanel p = new JPanel();
public void init()
{ p.setLayout(new GridLayout(2,2));
p.add(b0); p.add(b1); p.add(b2); p.add(b3);
add(p);
}
}
import java.awt.*;
import javax.swing.*;
GridLayout Panel Demo
public class GridLayoutPanelDemo extends JApplet
{
JButton b1 = new JButton("One");
JButton b2 = new JButton("Two");
JButton b3 = new JButton("Three");
JButton b4 = new JButton("Four");
JButton b5 = new JButton("Five");
JButton b6 = new JButton("Six");
JButton b7 = new JButton("Seven");
JButton b8 = new JButton("Eight");
JButton b9 = new JButton("Nine");
JPanel p = new JPanel(new
GridLayout(3,2));
public void init()
{
setLayout(new FlowLayout());
add(b1);
add(b2);
add(b3);
add(b4);
add(p);
p.add("North",b5);
p.add("West",b6);
p.add("Center",b7);
p.add("East",b8);
p.add("South",b9);
}
}
import java.awt.*;
import javax.swing.*;
public class PanelDemo extends JApplet
{
JButton b1 = new JButton("One"), b2 = new JButton("Two"), b3 = new JButton("Three”), b4 = new JButton("Four”);
JButton b5 = new JButton("Five"), b6 = new JButton("Six”), b7 = new JButton("Seven");
JTextArea ta1 = new JTextArea(5,15), ta2 = new JTextArea(5,15), ta3 = new JTextArea(5,15);
JTextField tf1 = new JTextField(15), tf2 = new JTextField(15);
JComboBox c1 = new JComboBox();
JPanel p1 = new JPanel(), p2 = new JPanel (new BorderLayout()), p3 = new JPanel (new GridLayout(2,1));
JPanel p4 = new JPanel (new BorderLayout()), p5 = new JPanel(), p6 = new JPanel(), p7 = new JPanel();
public void init()
{
setLayout(new FlowLayout());
add(b1);
add(p1);
p1.add(b2);
add(p2);
p2.add("North",b3);
p2.add("West",c1);
p2.add("East",ta3);
p2.add("South",tf1);
add(p3);
p3.add(b4);
p3.add(ta1);
add(p4);
p4.add("North",p5);
p5.add(b5);;
p4.add("Center",p6);
p6.add(ta2);
p4.add("South",p7);
p7.add(tf2);
}
}
import java.awt.*;
import javax.swing.*;
public class AddPanelDemo extends JApplet
{
JPanel pa = new JPanel();//defaults to FlowLayout
JButton b = new JButton ("Help");
JTextField tf = new JTextField("Enter name here",20);
JTextArea ta = new JTextArea("HELLO",5,20);
public void init()
{
add(pa);
pa.add(b); pa.add(tf); pa.add(ta);
}
}
import java.awt.*;
import javax.swing.*;
public class AddPanelDemo extends JApplet
{
JPanel pa = new JPanel(); //defaults to FlowLayout
JButton b = new JButton ("Help");
JTextField tf = new JTextField("Enter name here",20);
JTextArea ta = new JTextArea("HELLO",5,20);
public void init()
{
add(pa);
pa.add(b); pa.add(tf); pa.add(ta,0);
}
}
Example
Text Figure 4.2
import java.awt.*;
import java.applet.Applet;
What we want to achieve:
button1
list1
textfield
public class TrivialApplet extends Applet
{
// These declarations could be done in any order.
Panel panelA = new Panel();
Panel panelB = new Panel();
Panel panelA1 = new Panel();
Panel panelA2 = new Panel();
Button button1 = new Button("button1");
Button button2 = new Button("button2");
List list1 = new List();
List list2 = new List();
TextField textfield = new TextField("textfield");
Choice choice = new Choice();
panelA1
button2
list2
public void init()
{ // Now we build the containment hierarcy, from the
// botton up.
choice
panelA1.add(button1);
panelA1.add(list1); // done with panelA1
panelA2
panelA
panelB
panelA2.add(button2);
panelA2.add(list2); // done with panelA2
applet
panelA.add(panelA1);
panelA.add(panelA2); // done with panelA
Will this code do it?
panelB.add(textfield);
panelB.add(choice); // done with panelB
add(panelA); // add panelA to the applet
add(panelB); // add panelB to the applet -- finished!
}
}
Result
Text Figure 4.2
What we get:
import java.awt.*;
import java.applet.Applet;
public class TrivialApplet extends Applet
{
// These declarations could be done in any order.
Panel panelA = new Panel(new GridLayout(2,1));
Panel panelB = new Panel(new GridLayout(2,1));
Panel panelA1 = new Panel();
Panel panelA2 = new Panel();
Button button1 = new Button("button1");
Button button2 = new Button("button2");
List list1 = new List();
List list2 = new List();
TextField textfield = new TextField("textfield");
Choice choice = new Choice();
public void init()
{
panelA1.add(button1);
panelA1.add(list1); // done with panelA1
Stretched -
panelA2.add(button2);
panelA2.add(list2); // done with panelA2
panelA.add(panelA1);
panelA.add(panelA2); // done with panelA
panelB.add(textfield);
panelB.add(choice); // done with panelB
add(panelA); // add panelA to the applet
add(panelB); // add panelB to the applet -- finished!
}
}
Text Figure 4.2
import java.awt.*;
import java.applet.Applet;
What we get:
public class TrivialApplet extends Applet
{
// These declarations could be done in any order.
Panel panelA = new Panel(new GridLayout(2,1));
Panel panelB = new Panel(new GridLayout(2,1));
Panel panelA1 = new Panel();
Panel panelA2 = new Panel();
Button button1 = new Button("button1");
Button button2 = new Button("button2");
List list1 = new List();
List list2 = new List();
TextField textfield = new TextField("textfield");
Choice choice = new Choice();
public void init()
{
setLayout(new GridLayout(1,2));
panelA1.add(button1);
panelA1.add(list1); // done with panelA1
panelA2.add(button2);
panelA2.add(list2); // done with panelA2
panelA.add(panelA1);
panelA.add(panelA2); // done with panelA
panelB.add(textfield);
panelB.add(choice); // done with panelB
add(panelA); // add panelA to the applet
add(panelB); // add panelB to the applet -- finished!
}
}
Text Figure 4.2
import java.awt.*;
import java.applet.Applet;
What we get:
public class TrivialApplet extends Applet
{
// These declarations could be done in any order.
Panel panelA = new Panel(new GridLayout(2,1));
Panel panelB = new Panel(new GridLayout(2,1));
Panel panelA1 = new Panel();
Panel panelA2 = new Panel();
Button button1 = new Button("button1");
Button button2 = new Button("button2");
List list1 = new List();
List list2 = new List();
TextField textfield = new TextField("textfield");
Choice choice = new Choice();
public void init()
{
setLayout(new BorderLayout());
panelA1.add(button1);
panelA1.add(list1); // done with panelA1
panelA2.add(button2);
panelA2.add(list2); // done with panelA2
panelA.add(panelA1);
panelA.add(panelA2); // done with panelA
panelB.add(textfield);
panelB.add(choice); // done with panelB
add(“West”,panelA); // add panelA to the applet
add(“East”,panelB); // add panelB to the applet -- finished!
}
}
import java.awt.*;
import java.applet.Applet;
What we get:
public class TrivialApplet extends Applet
{
// These declarations could be done in any order.
Panel panelA = new Panel(new GridLayout(2,1));
Panel panelB = new Panel(new GridLayout(2,1,5,5));
Panel panelA1 = new Panel();
Panel panelA2 = new Panel();
Panel mainPanel = new Panel(new FlowLayout());
Button button1 = new Button("button1");
Button button2 = new Button("button2");
List list1 = new List();
List list2 = new List();
TextField textfield = new TextField("textfield");
Choice choice = new Choice();
public void init()
{
panelA1.add(button1);
panelA1.add(list1); // done with panelA1
panelA2.add(button2);
panelA2.add(list2); // done with panelA2
panelA.add(panelA1);
panelA.add(panelA2); // done with panelA
panelB.add(textfield);
panelB.add(choice); // done with panelB
mainPanel.add(panelA); // add panelA to the applet
mainPanel.add(panelB); // add panelB to the applet -- finished!
add(mainPanel);
}
}
Some Container Methods
import java.awt.*;
import java.applet.Applet;
public class Demo extends Applet
{ Panel pa = new Panel();
Button b = new Button ("Help");
TextField tf = new TextField("Enter name here",25);
TextArea ta = new TextArea("HELLO",5,20);
public void init()
{
pa.add(b); pa.add(tf); pa.add(ta,0);
add(pa);
pa.remove(b); // remove a component
}
}
import java.awt.*;
import java.applet.Applet;
public class Demo extends Applet
{ Panel pa = new Panel();
Button b = new Button ("Help");
TextField tf = new TextField("Enter name here",25);
TextArea ta = new TextArea("HELLO",5,20);
public void init()
{
pa.add(b); pa.add(tf); pa.add(ta,0);
add(pa);
int cnt = pa.countComponents();
System.out.println(“Num of components is “ + cnt);
}
}
Why Do We Need Layout Managers?
• Why don’t we just place components at some given position in a container?
• Reason:
to ensure that the GUI elements for your java program are displayed
properly in every possible Java environment.
• Layout managers automatically adjust components to fit the space that is available.
• If you fix the size and position of each of the components, some of the components
could run into one another and overlay if the screen area available to your program is
reduced.
• However, if you really don’t want to use a layout manager, you can remove the default
layout manager by setting a null layout.
setLayout(null);
or
panel1.setLayout(null);
• Now you must set the size and position for the components you place in the container
(relative to the coordinate system for the container).
import java.awt.*;
import javax.swing.*;
Absolute Positioning of GUI Objects
public class NullLayoutDemo extends JApplet
{
JLabel greeting = new JLabel("Hello -- welcome to my java applet");
JLabel prompt = new JLabel ("Please enter your name:");
JTextField inputLine = new JTextField(20);
JButton continueButton = new JButton( "Continue");
int xPos = 0, yPos = 0;
public void init()
{
//setLayout(null);
// add the components and set their location
add(greeting);
greeting.setLocation(0,0);
add(prompt);
prompt.setLocation(10,50);
add(inputLine);
inputLine.setLocation(10,100);
add(continueButton);
continueButton.setLocation(15,150);
}
}
setLocation is ignored since the
default is BorderLayout.CENTER
The result when the
setLayout(null)
command is uncommented.
import java.awt.*;
import javax.swing.*;
Absolute Positioning of GUI Objects (continued)
public class NullLayoutDemo extends JApplet
{
JLabel greeting = new JLabel("Hello -- welcome to my java applet");
JLabel prompt = new JLabel ("Please enter your name:");
JTextField inputLine = new JTextField(20);
JButton continueButton = new JButton( "Continue");
int xPos = 0, yPos = 0;
public void init()
{
setLayout(null);
// add the components and set their location
// add the components and set their location
add(greeting);
greeting.setBounds(5,5,40,10);
add(prompt);
prompt.setBounds(10,30,20,10);
add(inputLine);
inputLine.setBounds(10,100,25,30);
add(continueButton);
continueButton.setBounds(15,150,20,5);
}
}
import java.awt.*;
import java.applet.Applet;
Absolute Positioning of GUI Objects (continued)
public class NullLayoutDemo extends Applet
{
Label greeting = new Label("Hello -- welcome to my java applet");
Label prompt = new Label ("Please enter your name:");
TextField inputLine = new TextField(20);
Button continueButton = new Button( "Continue");
int xPos = 5, yPos = 5;
int w = 100, h = 20;
public void init()
{
setLayout(null);
// add the components and set their location
add(greeting);
greeting.setBounds(xPos,yPos,2*w,2*h);
add(prompt);
prompt.setBounds(6*xPos,yPos+3*h,2*w,yPos+h);
add(inputLine);
inputLine.setBounds(xPos,yPos+5*h,2*w,yPos+h);
add(continueButton);
continueButton.setBounds(8*xPos,7*h,w,yPos+h);
}
}
import java.awt.*;
import javax.swing.*;
Absolute Positioning of GUI Objects (continued)
public class NullLayoutDemo extends JApplet
{
JLabel greeting = new JLabel("Hello -- welcome to my java applet");
JLabel prompt = new JLabel ("Please enter your name:");
JTextField inputLine = new JTextField(20);
JButton continueButton = new JButton( "Continue");
int xPos = 5, yPos = 5, width = 100, height = 20;
public void init()
{
setLayout(null);
// add the components
add(greeting);
add(prompt);
add(inputLine);
add(continueButton);;
// set both the components size and location
greeting.setSize(300,20);
greeting.setLocation(5,5);
prompt.setSize(150,20);
prompt.setLocation(25,25);
inputLine.setSize(150,20);
inputLine.setLocation(12,60);
continueButton.setSize(90,20);
continueButton.setLocation(60,100);
}
}