The Applet Class
An Applet does not have a main method. An Applet is a program that is loaded and executed by another program – usually a browser or appletviewer.
An applet reference line can be contained within HTML code.
(put the following line in any html file and to run the SampleApplet.class)
<applet code =
SampleApplet.class width = 500 height = 500>
</applet>
When an Applet
is embedded in an HTML page, it is downloaded remotely across the Net and run
on your PC.
Applet Source Code
The source is used to compile an applet class.
import java.awt.*;
import
java.applet.Applet;
public class
SampleApplet extends Applet {
private static int initCount= 0;
private static int paintCount = 0;
public void init(){
// Called when the applet is loaded
initCount++; // increase every time the init() is called
setBackground(Color.yellow);
setForeground(Color.blue);
}
public void paint(Graphics g) { // another override
// Called by the browser when the applet
is to be drawn.
// or when suggested by repaint().
paintCount++; // increased every time paint() is called
g.setFont(new
Font("SansSerif", Font.ITALIC, 12));
g.drawString("init() method
activated " + initCount
+ " time" + ((initCount!=
1)?"s":" "), 20, 20);
g.setFont(new
Font("Serif", Font.BOLD + Font.ITALIC, 14));
g.drawString("paintCount()
method activated " + paintCount
+ "
time" + ((paintCount != 1)?"s":" "), 20, 40);
}
}
To run the applet, activate the HTML code which contains
the reference to the applet.
Applet limitation: Applets embedded within web pages are not allowed to do local disk I/O.
Applet Methods
|
Applet Methods |
Action |
|
resize(int width, int height) |
Request applet be resized* |
|
init() |
Initialize variables |
|
start() |
Start execution |
|
stop() |
Stops execution |
|
destroy() |
Release resources |
|
paint(Graphics g) |
Paint -- Inherited from parent |
|
repaint(Graphics g) |
Suggestion to Paint -- Inherited from parent* |
|
|
* Methods the programmer can call All other methods are called by the system |
Screen
Coordinates are used for Positioning Graphics --
A point on the screen is a picture element (pixel). The pixel is positioned at the intersection of its horizontal and vertical coordinates.
· The horizontal coordinate (horiz) starts as zero at the left. Increasing the value of horiz moves the pixel further to the right.
· The vertical coordinate (vert) starts as zero at the top. Each increase in the value of vert moves the pixel further to the bottom.
The width and height of a graphic object is measured in pixels.
· Width (w). As w increases, the object is wider.
· Height (h). As h increases, the object is taller.
In order
to accomplish a task, the Applet needs overrides to parent methods
and work done by
other classes such as Graphics, Color and Font.
Color
The Color class represents colors as having levels
of Red, Green and Blue saturation.
Every color has an implicit value of 255 for full
saturation.
Explicit values to the constructor can range from 0
to 255.
|
Color Constructors |
Action |
|
Color(int red, int green, int blue) |
Creates a color with the specified values (0 – 255) |
|
Color(float red, float green, float
blue) |
Creates a color with the specified values |
|
Color(redGreenBlue) |
Creates a color with the specified values blue in bits 0-7, green in bits 8-15, red in 16-23 |
|
Color Methods |
Action |
|
Color brighter() |
Creates a brighter version of current Color |
|
Color darker() |
Creates a darker version of current Color |
|
int getBlue() |
Returns the blue component (0-255) |
|
int getGreen() |
Returns the green component (0-255) |
|
int getRed() |
Returns the red component (0-255) |
|
Color Constants |
|
|
black, blue, cyan, darkGray, gray,
green, lightGray, magenta, orange, pink, red, white, yellow |
|
/* Draw
each of 100 cells with randomly
* chosen colors.
*/
import
java.awt.*;
import
java.applet.Applet;
public
class ColorChips extends Applet {
public void paint(Graphics g) {
int h =
getSize().height;
int w =
getSize().width;
for (int i = 0; i
< 10; i++)
for (int j = 0;
j < 10; j++) {
float red =
(float)Math.random();
float green =
(float)Math.random();
float blue =
(float)Math.random();
Color
color = new Color(red,green,blue);
g.setColor(color);
g.fillRect(i*w/10,j*h/10,w/10,h/10);
}
}
}
Font
The Font class represents fonts for textual display.
Five font names are recognized by any Java environment: SansSerif, Serif,
Mono-space d, Dialog and DialogInput.
|
Font Constructor |
Action |
|
Font(String name, int style, int size) |
Creates a Font with the specified values |
|
Font Methods |
Action |
|
String getName() |
returns the name of the font |
|
int getSize() |
returns the size |
|
int getStyle() |
returns the style |
|
Font Constants |
|
|
BOLDfg, ITALIC, PLAIN |
|
//Copyright
(c) 1998-2001, Art Gittleman
/*
Draws the different fonts, trying all the
* styles, and using
various point sizes. Draws
* all text relative to
the applet's size. Uses
* the init method to
compute quantities that
* don't change.
*/
import
java.awt.*;
import
java.applet.Applet;
public
class Text extends Applet {
private Font
arialBold24;
private Font
timesItalic14;
private Font courierPlain18;
private Font
lucindaBI20;
private Font
serifPlain18;
private String
arial; // The string we want to center
private int
arialStart; // x position for the centered string
private int
arialWide; // The width of the centered string.
public void init() {
arialBold24 = new Font("Arial",Font.BOLD,24);
timesItalic14 = new Font("Times
New Roman",Font.ITALIC,14);
courierPlain18 = new Font("Courier",Font.PLAIN,18);
lucindaBI20 = new Font
("Lucinda Sans Regular",Font.BOLD+Font.ITALIC,20);
serifPlain18 = new Font("Serif",Font.PLAIN,18);
setFont(arialBold24);
FontMetrics metrics = getFontMetrics(arialBold24);
arial =
arialBold24.getName();
arialWide =
metrics.stringWidth(arial);
}
public void
paint(Graphics g) {
Dimension d = getSize();
int w =
d.width; // The width of the applet
int h =
d.height; // The height of the applet
int arialStart =
(w-arialWide)/2;
int otherStart =
w/4;
g.drawString(arial,arialStart,h/6);
g.setFont(timesItalic14);
g.drawString(timesItalic14.getName(),otherStart,2*h/6);
g.setFont(courierPlain18);
g.drawString(courierPlain18.getName(),otherStart,3*h/6);
g.setFont(lucindaBI20);
g.drawString(lucindaBI20.getName(),otherStart,4*h/6);
g.setFont(serifPlain18);
g.drawString(serifPlain18.getName(),otherStart,5*h/6);
}
}
Graphics
Each Applet has a Graphics object associated with it.
Access to the graphics object is
provided as a parameter to paint(Graphics g).
|
Graphic Methods |
Action |
|
clearRect(int horiz, int vert, int w,
int h) |
Clears the specified rectangle by filling it with the background color of the current drawing surface. |
|
Draw3DRect (int horiz, int vert, int w,
int h,
boolean raised) |
Draws a 3-D highlighted outline of the specified rectangle. |
|
drawArc (int horiz, int vert, int w,
int h,
int startAngle, int arcAngle) |
Draws the outline of a circular or elliptical arc covering the specified rectangle. |
|
drawLine(int horiz1, int vert1, int
horiz2,
int vert2) |
Draws a line between horiz1,vert1 and horiz2, vert2 |
|
drawOval(int horiz, int vert, int w,
int h) |
Draws an oval outline |
|
drawPolygon(int[] horiz, int[] vert,
int nbrOfpoints |
Draws a sequence of connected lines |
|
drawRect(int horiz, int vert, int w,
int h) |
Draws outline of a rectangle |
|
drawString(String str, int horiz, int
vert) |
Draws the text |
|
Fill3DRect(int horiz, int vert, int w,
int h,
boolean raised) |
Highlighted rectangle, filled with current color |
|
fillArc(int horiz, int vert, int w, int
h,
int startAngle, int arcAngle) |
Fills a circular arc |
|
fillOval(int horiz, int vert, int w,
int h) |
Fills an oval |
|
fillPolygon(int[] horiz, int[] vert,
int nbrOfpoints |
Fills a closed polygon |
|
fillRect(int horiz, int vert, int w,
int h) |
Fills the rectangle |
|
setColor(Color c) |
Sets the color |
|
setFont(Font f) |
Sets the font |
//Copyright
(c) 1998, Arthur Gittleman
/* Demonstrates
drawing and filling 3D
* rectangles, and brightening and
darkening
* colors.
*/
import
java.awt.*;
import
java.applet.Applet;
public
class MoreColor extends Applet {
public void
paint(Graphics g) {
g.setColor(Color.orange);
g.fillRect(10,20,100,50);
g.fill3DRect(150,20,100,50,true);
g.fill3DRect(270,20,100,50,false);
g.setColor(Color.orange.darker());
g.fillOval(10,100,100,50);
g.setColor(Color.orange.brighter());
g.fillOval(150,100,100,50);
g.setColor(Color.orange);
g.draw3DRect(10,180,100,50,true);
g.draw3DRect(150,180,100,50,false);
g.setColor(Color.black);
g.drawString("
g.drawString("3-d
Raised",150,90);
g.drawString("3-d
Recessed",270,90);
g.drawString("Darker",25,170);
g.drawString("Brighter",170,170);
g.drawString("3-d
Raised",20,250);
g.drawString("3-d
Recessed",160,250);
}
}
Abstract Windows Toolkit Class Hierarchy
The paint()method called in the sample Applet is not a method defined at the Applet level.
The Applet inherits methods from its parent classes
The Abstract Windowing Toolkit (AWT)
is a single programmer interface (API) for dealing with common GUI components across different platforms.
The AWT library delegates the creation and behavior of the interface elements to the native GUI toolkit on each target platform.
Appearance of the GUI
is dependent on the platforms executing the GUI.
Windows API
OS/2 Presentation Manager API
X-Windows API
Mac API
Component
A component is an object with a graphical representation that can interact with the user.
Examples of components are the buttons, checkboxes, and scrollbars.
|
Component Methods |
Action |
|
add(Component comp) |
Adds the Component to the end of this container |
|
add(Component comp, int index) |
Adds the Component to the index position |
|
paint(graphics g) |
Causes this component to be painted using the graphics object g. * |
|
remove(Component comp) |
Removes the specified Component |
|
remove(int index) |
Removes the Component at index |
|
removeAll() |
Removes all the Components from the container |
|
repaint() |
Tell the system that this component needs to be redrawn |
|
repaint(int horiz, int vert, int w, int
h) |
Redraw the component at a given location and size |
|
setBackground(Color c) |
Sets background color |
|
setBounds(int horiz, int vert, int w,
int h) |
Changes the size and location of the Component |
|
setFont(Font f) |
Sets the Font of the Component |
|
setForeground(Color c) |
Sets the foreground color |
|
setLayout(LayoutManager mgr) |
Sets the layout manager for this container |
|
setLocation(int horiz, int vert) |
Changes the location of the Component |
|
setSize(int w, int h) |
Changes the size of the Component |
|
update() |
Default behavior is to erase Component by drawing over it with background color then call the paint() method. *. |
|
|
*Called by the System |
Subclasses of Component
Component is an abstract class. The subclasses of Component define the Component methods above and add methods specialized to their purpose.
Button
A Button is a graphic component that can be clicked.
|
Button Constructors |
Action |
|
Button() |
Creates a Button with no title |
|
Button(String s) |
Creates a Button labeled with
the String given |
|
Button Methods |
|
|
String getLabel() |
Returns the Button’s text label |
|
setLabel(String s) |
Replaces the label of the Button
with the String s |
Canvas
A Canvas component is a blank rectangular area onto
which the program can draw and/or trap input events from the user
The Canvas class should be extended in order to
customize its appearance. Override paint() to perform custom graphics.
|
Canvas Constructor |
Action |
|
Canvas() |
Creates a Canvas |
|
Canvas Methods |
|
|
paint(Graphics g) |
Called when the canvas will be
painted |
Checkbox
A Checkbox displays
a toggle button. It has a boolean member indicating
its state.
A check box can be in either an "on" (true) or "off"
(false)
state. Clicking on a check box changes its state from "on" to
"off," or from "off" to "on."
|
Checkbox Constructors |
Action |
|
Checkbox(String s) |
Creates a Checkbox with the
label of the String given and sets the state to false |
|
Checkbox(String s, boolean b) |
In addition to above, sets the
state to b. |
|
Checkbox(String s, boolean b,
CheckboxGroup g) |
In addition to above, assigns
Checkbox to a CheckboxGroup. |
|
Checkbox Methods |
|
|
String getLabel() |
Returns the Checkbox’s text |
|
boolean getState() |
returns the current state (true
or false) |
|
setLabel(String s) |
Replaces the label of the
Checkbox with the String s |
|
setState(boolean b) |
Replaces the state with b |
|
setCheckboxGroup(CheckboxGroup g) |
Assigns Checkbox to a
CheckboxGroup |
CheckboxGroup (aka
radio buttons)
CheckboxGroup has no visual appearance and is not a
subclass of Component.
CheckboxGroup provides a way to collect
related Checkboxes – only one of which can be true at any one time.
Pushing any button sets its state to "on" and forces any other button that is in the "on" state into the "off" state.
|
CheckboxGroup Constructor |
Action |
|
CheckboxGroup() |
Creates a CheckboxGroup |
|
CheckboxGroup Methods |
|
|
Checkbox getSelectedCheckbox() |
Returns the Checkbox’s which has
the true state |
|
setSelectedCheckbox(Checkbox c) |
Sets the state of Checkbox to
true and turns other Checkboxes off |
Choice
Choice
presents a pop-up menu of choices. The current choice is
displayed as the title of the menu.
|
Choice Constructor |
Action |
|
Choice() |
Creates a Choice |
|
Choice Methods |
|
|
add (String item) |
Adds an item to the choice list |
|
String getItem(int index) |
Gets the String at index |
|
int getSelectedIndex() |
Gets index of currently selected
item |
|
String getSelectedItem() |
Gets String of item selected |
|
insert(String item, int index) |
Inserts item at index |
|
remove(int position) |
Removes item at given position |
|
remove(String item) |
Removes first occurrence of item |
|
removeAll() |
Removes all items |
|
select(int index) |
Sets the selection to index |
|
select(String item) |
Selects matching string |
Label
A Label displays a single line of text.
A user cannot edit the text but it is changeable by the program.
|
Label Constructors |
Action |
|
Label(String s) |
Creates a center-aligned Label
displaying the String given |
|
Label(String s, int alignment) |
Creates a Label according to the
alignment given and String Label.LEFT, Label.RIGHT, Label.CENTER |
|
Label Methods |
|
|
String getText() |
Returns the Label’s text |
|
setText(String s) |
Replaces the text in the Label
with the String s |
List
List looks
like a text area with a scrolling list of items.
The List
can be set up so that the user can choose either one item or
multiple items.
|
List Constructor |
Action |
|
List() |
Creates a List in single
selection mode |
|
List(int rows) |
In addition to above, sets the
number of rows |
|
List(int rows, boolean m) |
In addition to above, sets
multiple selection if m is true |
|
List Methods |
|
|
add(String item) |
Adds an item to the list |
|
add(String item, int index) |
Adds item at index |
|
addItem(String item) |
Adds an item |
|
deselect(int index) |
Turns off selection |
|
String getItem(int index) |
Gets the String at index |
|
int getSelectedIndex() |
Gets index of currently selected
item |
|
int[] getSelectedIndexes() |
Get selected indexes |
|
String getSelectedItem() |
Gets current selection as a
String |
|
String [] getSelectedItems() |
Gets all selected items as a
String array |
|
remove(int position) |
Removes item at given position |
|
remove(String item) |
Removes first occurrence of item |
|
removeAll() |
Removes all items |
|
select(int index) |
Sets the selection to index |
TextField
A TextField
looks like a box with one line of text.
A user can edit the text and it is changeable by the program.
|
TextField Constructors |
Action |
|
TextField(int columns) |
Creates a empty TextField wide
enough to hold columns |
|
TextField(String s) |
Creates a TextField displaying
the String given |
|
TextField (String s, int columns) |
Shows text within columns |
|
TextField Methods |
|
|
String getText() |
Returns the text.* |
|
setEchoChar(char c) |
Echo character prints instead of
what is keyed |
|
setText(String s) |
Replaces the text with the String
s |
|
setColumns(int l) |
Changes the number of columns to
l |
TextArea
A TextArea
looks like a box with multiple lines of text.
A user can edit the text and it is changeable by the program.
|
TextArea Constructors |
Action |
|
TextArea(int r, int c) |
Creates empty TextArea with r rows and c columns |
|
TextArea(String s) |
Creates a TextArea displaying
the String given |
|
TextArea(String s, int r, int c) |
Shows text within columns with r rows and c columns |
|
TextArea(String s, int r, int c, int
scrollbars) |
Specify whether the area will
have scrollbars TextArea.SCROLLBARS_BOTH, TextArea.SCROLLBARS_NONE, TextArea.SCROLLBARS_HORIZONTAL_ONLY, TextArea.SCROLLBARS_VERTICAL_ONLY |
|
TextArea Methods |
|
|
append(String s) |
Concatenates s to currently
existing TextArea |
|
String getText() |
Returns the text.* |
|
setText(String s) |
Replaces the text with the
String s |
|
setColumns(int l) |
Changes the number of columns to
l |
|
setRows(int r) |
Changes the number of rows to r |
import
java.awt.*;
import
java.applet.Applet;
public
class ComponentsAndContainers extends Applet {
Panel panel;
public void init() {
Button b = new Button("Button");
b.setSize(100,50);
add(b);
add(new Checkbox("Checkbox"));
List list = new List(3);
list.add("ice");
list.add("nice");
list.add("mice");
add(list);
panel = new MyPanel();
panel.setBackground(Color.blue);
panel.add(new
Button("Inside Panel"));
add(panel);
CheckboxGroup group = new CheckboxGroup();
add(new
Checkbox("This", true, group));
add(new
Checkbox("That", false, group));
add(new
Checkbox("Other", false, group));
DrawOn canvas
= new DrawOn();
canvas.setBackground(Color.yellow);
canvas.setSize(150,150);
add(canvas);
}
}
class
MyPanel extends Panel {
public Dimension
getPreferredSize() {
return new
Dimension(100,100);
}
}
class
DrawOn extends Canvas {
public void
paint(Graphics g) {
g.drawString("Inside
Canvas",20,20);
}
}
Containers
A Container is a Component used to hold other components together for display purposes.
Since Container is a subclass of Component, it has access to all the component methods listed above.
Components added to a Container are added to the end of the list unless an index position is specified.
There is no limit to the number of components a Container may hold.
|
Container Methods |
Action |
|
add(Component c) |
Adds the Component to the end of this container |
|
add(Component c, Object constraints) |
Adds the Component with specified constraint |
|
Component[] getComponenets() |
Gets all the components in this container |
|
boolean isAncestorOf(Component c) |
Checks if the component is contained in the hierarchy of this container |
|
remove(Component comp) |
Removes the specified Component |
|
remove(int index) |
Removes the Component at index |
|
removeAll() |
Removes all the Components from the container |
|
setFont(Font f) |
Sets the font |
|
setLayout(LayoutManager mgr) |
Sets the layout manager for the container |
Container Hierarchy
There is no limit to how deeply they may be nested – Containers within Containers, etc.
If a container is removed, all the components in that container are also removed.
Subclasses of Container
Container is an abstract class. The subclasses of Container add methods specialized to their purpose.
|
Container |
Use |
Default
Layout Manager |
|
Panel |
The
simplest Container class |
FlowLayout |
|
Applet |
Extends
Panel Displays
components in a Web browser. Applets
do not have a menu bar. |
FlowLayout |
|
Frame |
Full
functioning window with its own title and border. |
BorderLayout |
|
Window |
Top-level
window with no borders nor menubar |
BorderLayout |
|
Dialog |
Top-Level
window with title and border. Used as
“auxiliary” windows for input to stand-alone applications. |
BorderLayout |
LayoutManager
A LayoutManager determines the size, position and
arrangement of components within a container.
LayoutManagers differ in how the components are
arranged.
Some arrange the components in rows while others divide the display into regions.
FlowLayout
A FlowLayout arranges Components from left to
right until no more components will fit in a row – then another row is
started.
|
FlowLayout Methods |
Action |
|
setAlignment(int align) |
Sets the alignment for this layout FlowLayout.CENTER, FlowLayout.LEFT, FlowLayout.RIGHT |
|
setHgap(int hgapPixels) |
Sets the horizontal gap between components |
|
setVgap(int vgapPixels) |
Sets the vertical gap between components |
FlowLayout Example:
import java.awt.*;
import
java.applet.Applet;
public class Flow extends Applet {
public Flow () {
setLayout(new
FlowLayout()); // Applet uses FlowLayout by default
add(new
Button("1"));
add(new
Button("2"));
add(new
Button("3"));
add(new
Button("4"));
add(new
Button("5"));
add(new
Button("6"));
}
}
BorderLayout
A BorderLayout divides a Container into 5 regions: North, South, East, West, and Center.
Each region can hold one Component.
Components may be resized to completely fill each
region.
|
BorderLayout Methods |
Action |
|
setHgap(int hgapPixels) |
Sets the horizontal gap between components |
|
setVgap(int vgapPixels) |
Sets the vertical gap between components |
|
BorderLayout Constants |
|
|
CENTER, EAST, NORTH, SOUTH, WEST |
|
BorderLayout Example:
import java.awt.*;
import java.applet.Applet;
public class Border extends Applet {
public Border () {
setLayout(new
BorderLayout());
add(new
Button("North 1"),
BorderLayout.NORTH);
add(new
Button("South 2"),
BorderLayout.SOUTH);
add(new
Button("East 3"), BorderLayout.EAST);
add(new
Button("West 4"),
BorderLayout.WEST);
add(new
Button("Center 5"), BorderLayout.CENTER);
add(new
Button(“Center 6”), BorderLayout.CENTER);
// last one in wins!
}
}
Modify the program above so that the CENTER regions contains buttons Center 5 and Center 6.
GridLayout
A GridLayout divides a Container into rows and columns to form a rectangular grid.
Each rectangle can hold one
Component.
When adding Components, they will fill the cells
from left to right, top to bottom order.
Components may be resized to completely fill each
region.
Each Component will be the same size.
|
GridLayout Constructor |
|
|
GridLayout(int r, int c) |
Creates a grid layout with r rows and c columns |
|
GridLayout Methods |
|
|
setHgap(int hgapPixels) |
Sets the horizontal gap between components |
|
setVgap(int vgapPixels) |
Sets the vertical gap between components |
GridLayout Example:
import java.awt.*;
import
java.applet.Applet;
public class Grid extends Applet {
public void init ()
{
int row = 3, col =
2;
setLayout(new
GridLayout(row, col));
add(new
Button("Button 1"));
add(new
Button("Button 2"));
add(new
Button("Button 3"));
add(new
Button("Button 4"));
add(new
Button("Button 5"));
add(new Button("Button 6"));
}
}
GridBagLayout
A GridBagLayout aligns components by a rectangular grid of vertical and horizontal cells.
Each Component can occupy one or more cells (display area).
The Components can be different
sizes.
Each Component is associated with an instance of GridBagConstraints.
GridBagConstraints hold the values that customize the locations and appearance of each component.
Alter the values of the constraint variables to alter the display of the components
GridBagConstraints
|
GridBagConstraints Variables |
Layout |
||||||||
|
Gridx, Gridy |
Leading corner of the display area. Use:
|
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|
gridwidth, gridheight |
Specifies the number of cells in a row (for or column (for Use:
|
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|
Fill |
Used when the component's display area is larger than the component's requested size to determine whether (and how) to resize the component Use:
|
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|
Ipadx, Ipady |
How much internal padding to add to the minimum size of the component. The value entered will be multiplied by 2 pixels (for both sides) |
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|
insets |
How much external padding surrounds the component – minimum amount of space between the component and the edges of its display area. |
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|
anchor |
Used when the component is smaller than its display area to determine where (within the display area) to place the component. Use: NORTH, SOUTH, WEST, EAST, NORTHWEST,
NORTHEAST, SOUTHWEST, SOUTHEAST, CENTER |
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|
weightx, weighty |
Weight of zero (default) clumps all components into the center of the container. |
GridBagLayout Example:
import java.awt.*;
import java.util.*;
import
java.applet.Applet;
public class
GridBagEx1 extends Applet {
protected void
makebutton(String name,
GridBagLayout
gridbag,
GridBagConstraints c) {
Button button = new Button(name);
gridbag.setConstraints(button,
c);
add(button);
}
public void
init() {
GridBagLayout gridbag = new GridBagLayout();
GridBagConstraints c = new GridBagConstraints();
setFont(new
Font("Helvetica", Font.PLAIN, 14));
setLayout(gridbag);
c.fill = GridBagConstraints.BOTH;
c.weightx = 1.0;
makebutton("Button1",
gridbag, c);
makebutton("Button2",
gridbag, c);
makebutton("Button3",
gridbag, c);
c.gridwidth = GridBagConstraints.REMAINDER;
//end row
makebutton("Button4",
gridbag, c);
c.weightx = 0.0; //reset to the default
makebutton("Button5",
gridbag, c); //another row
c.gridwidth =
GridBagConstraints.RELATIVE; //next-to-last in row
makebutton("Button6",
gridbag, c);
c.gridwidth =
GridBagConstraints.REMAINDER; //end row
makebutton("Button7",
gridbag, c);
c.gridwidth = 1; //reset to the default
c.gridheight = 2;
c.weighty = 1.0;
makebutton("Button8",
gridbag, c);
c.weighty = 0.0; //reset to the default
c.gridwidth =
GridBagConstraints.REMAINDER; //end row
c.gridheight = 1; //reset to the default
makebutton("Button9", gridbag, c);
makebutton("Button10",
gridbag, c);
setSize(300,
100);
}
}
Frame
A frame is a top-level window with a title and a border. A frame may also have scroll bars, a menu bar, etc.
|
Frame Constructors |
Action |
|
Frame() |
Creates a Frame |
|
Frame(String title) |
Creates a with given title |
|
Frame Methods |
|
|
setResizable(boolean resizable) |
Sets whether this frame is
resizable by the user |
|
setTitle(String title) |
Sets the title for this Frame |
|
show() |
Makes Container visible
(Inherited from Window) |
|
addWindowListener(WindowListener l) |
Adds the specified window
listener to receive window events |
Frames are capable of generating the following
types of WindowEvents:
WINDOW_OPENED
WINDOW_CLOSING
WINDOW_CLOSED
WINDOW_ICONIFIED
WINDOW_DEICONIFIED
WINDOW_ACTIVATED
WINDOW_DEACTIVATED
WINDOW_GAINED_FOCUS
WINDOW_LOST_FOCUS
WINDOW_STATE_CHANGED
Intro to Events – Calling a Frame from an Applet:
import
java.applet.Applet;
import
java.awt.*;
import java.awt.event.*;
public
class FrameExample extends Applet
implements
ActionListener, WindowListener {
Frame myFrame = new Frame("Entry
Test");
Label reasonLabel =
new
Label("Fill in the fields below, then click OK");
Label label1 = new Label("User
ID:", Label.RIGHT);
Label label2 = new Label("Password:",
Label.RIGHT);
TextField field1 = new TextField(15);
TextField field2 = new TextField(15);
Button OKButton = new Button("OK");
public void init()
{
myFrame.setBackground(Color.white);
reasonLabel.setFont(new
Font("SansSerif", Font.BOLD, 16));
field2.setEchoChar('*');
myFrame.add(BorderLayout.NORTH,
reasonLabel);
Panel pc = new Panel();
pc.setLayout(new
GridLayout(2,2,8,2));
pc.add(label1);
pc.add(field1);
pc.add(label2);
pc.add(field2);
myFrame.add(BorderLayout.CENTER,
pc);
Panel ps= new Panel();
ps.add(OKButton);
myFrame.add(BorderLayout.SOUTH,
ps);
OKButton.addActionListener(this);
myFrame.addWindowListener(this);
myFrame.setSize(300,175);
myFrame.show();
}
public void actionPerformed(ActionEvent e) {
myFrame.setVisible(false);
myFrame.dispose();
}
public void
windowActivated(WindowEvent evt) { }
public void
windowDeactivated(WindowEvent evt) { }
public void
windowClosed(WindowEvent event) { }
public void
windowDeiconified(WindowEvent event){ }
public void
windowIconified(WindowEvent event) { }
public void
windowOpened(WindowEvent event) { }
public void
windowClosing(WindowEvent event) {
myFrame.setVisible(false);
myFrame.dispose();
}
}
Intro to Events – Calling a Frame from an Application:
import java.awt.*;
import
java.awt.event.*;
public class FrameExample2 extends Frame
implements
ActionListener, WindowListener {
Label reasonLabel =
new
Label("Enter the data needed, then click OK to proceed");
Label label1 = new Label("User
ID:", Label.RIGHT);
Label label2 = new Label("Password:",
Label.RIGHT);
TextField field1 = new TextField(15);
TextField field2 = new TextField(15);
Button OKButton = new Button("OK");
String name = "";
String password = "";
public FrameExample2() { // constructor used instead of init()
super("Sign
on Screen");
setBackground(Color.white);
reasonLabel.setFont(new Font("SansSerif",
Font.BOLD, 16));
field2.setEchoChar('*');
add(BorderLayout.NORTH,
reasonLabel);
Panel pc = new Panel();
pc.setLayout(new
GridLayout(2,2,8,2));
pc.add(label1);
pc.add(field1);
pc.add(label2);
pc.add(field2);
add(BorderLayout.CENTER,
pc);
Panel ps= new Panel();
ps.add(OKButton);
add(BorderLayout.SOUTH,
ps);
OKButton.addActionListener(this);
addWindowListener(this);
}
public static void
main(String[] args){ // main added
FrameExample2 frame = new FrameExample2();
frame.setSize(400,150);
frame.show();
}
public void
windowActivated(WindowEvent evt) { }
public void
windowDeactivated(WindowEvent evt) { }
public void
windowClosed(WindowEvent event) { }
public void
windowDeiconified(WindowEvent event){ }
public void
windowIconified(WindowEvent event) { }
public void
windowOpened(WindowEvent event) {
}
public void
windowClosing(WindowEvent event) {
setVisible(false);
dispose();
}
public void
actionPerformed(ActionEvent e) {
name =
field1.getText();
password =
field2.getText();
if (name !=
null)
System.out.println("Username:
" + name
+ " Password: " + password);
setVisible(false);
dispose();
}
}