Transcript Dialogs

Dialogs
Displaying Text in a Dialog Box
• Windows and dialog boxes
– Up to this our output has been to the screen
– Many Java applications use these to display output
– Package is javax.swing – contains classes for
creation of GUIs.
– JOptionPane class provides prepackaged dialog
boxes called message dialogs
– showMessageDialog() – displays a dialog box
displaying a message. Two parameters , position of
the dialog box and the message.
Displaying Text in a Dialog Box
// Printing multiple lines in dialog box.
import javax.swing.JOptionPane; // import class JOptionPane
public class Dialog1
{
public Dialog1() {
// display a dialog with the message
Import );class JOptionPane
JOptionPane.showMessageDialog( null, "Welcome\nto\nJava"
}
public static void main( String args[] )
{
new Dialog1();
} // end main
} // end class Dialog1
Show a message dialog with text
Displaying Text in a Dialog Box
• showMessageDialog() – displays a dialog box displaying a
message. Two parameters , position of the dialog box and the
message.
• showMessageDialog() is a class method of JOptionPane class , it is
a static method.
• Such methods often define frequently used tasks that do not explicitly
require the creation of an object.
• A static method typically is called by using its class name dot
operator and the method name.
JOptionPane.showMessageDialog( null, "Welcome\nto\nJava" );
• Note we did not have to create an instance of the class JoptionPane
to use the showMessageDialog() method.
Entering Text in a Dialog Box
• Input dialog
– Allows user to input information
– Created using method
showInputDialog from class
JOptionPane
Entering Text in a Dialog Box
// Basic input with a dialog box.
import javax.swing.JOptionPane;
public class NameDialog
{
public NameDialog()
{
// prompt user to enter name
String name =JOptionPane.showInputDialog( "What is your name?" );
// create the message
String message = String.format( "Welcome, %s, to Java Programming!", name );
// display the message to welcome the user by name
JOptionPane.showMessageDialog( null, message );
}
public static void main( String args[] )
{
new NameDialog();
}
} // end class NameDialog
Entering Text in a Dialog Box
• showInputDialog() – parameter is the prompt
• The user types characters in the text field,
– User enters OK - showInputDialog() returns a String.
– User enters Cancel - showInputDialog() returns null
• static String method format() –returns a formatted String similar to
printf
Displaying Text in a Dialog Box
• Windows and dialog boxes
– Up to this our output has been to the screen
– Many Java applications use these to display output
– Package is javax.swing – contains classes for
creation of GUIs.
– JOptionPane class provides prepackaged dialog
boxes called message dialogs
– showMessageDialog() – displays a dialog box
displaying a message. Two parameters , position of
the dialog box and the message.
Displaying Text in a Dialog Box
// Printing multiple lines in dialog box.
import javax.swing.JOptionPane; // import class JOptionPane
public class Dialog1
{
public Dialog1() {
// display a dialog with the message
Import );class JOptionPane
JOptionPane.showMessageDialog( null, "Welcome\nto\nJava"
}
public static void main( String args[] )
{
new Dialog1();
} // end main
} // end class Dialog1
Show a message dialog with text
Displaying Text in a Dialog Box
• showMessageDialog() – displays a dialog box displaying a
message. Two parameters , position of the dialog box and the
message.
• showMessageDialog() is a class method of JOptionPane class , it is
a static method.
• Such methods often define frequently used tasks that do not explicitly
require the creation of an object.
• A static method typically is called by using its class name dot
operator and the method name.
JOptionPane.showMessageDialog( null, "Welcome\nto\nJava" );
• Note we did not have to create an instance of the class JoptionPane
to use the showMessageDialog() method.
Entering Text in a Dialog Box
• Input dialog
– Allows user to input information
– Created using method
showInputDialog from class
JOptionPane
Entering Text in a Dialog Box
// Basic input with a dialog box.
import javax.swing.JOptionPane;
public class NameDialog
{
public NameDialog()
{
// prompt user to enter name
String name =JOptionPane.showInputDialog( "What is your name?" );
// create the message
String message = String.format( "Welcome, %s, to Java Programming!", name );
// display the message to welcome the user by name
JOptionPane.showMessageDialog( null, message );
}
public static void main( String args[] )
{
new NameDialog();
}
} // end class NameDialog
Entering Text in a Dialog Box
• showInputDialog() – parameter is the prompt
• The user types characters in the text field,
– User enters OK - showInputDialog() returns a String.
– User enters Cancel - showInputDialog() returns null
• static String method format() –returns a formatted String similar to
printf
• Exercises
• Adapt our Hello World and Leap Year
programs to include Swing Input and
Output
Java packages
• Java Packages available with the JDK
–
–
–
–
java.io – for system input and output
java.math – for integer and decimal arithmetic
java.text - for handling text, dates, numbers …
java.util – for collections, date & time facilities also new
class Scanner for Data input
– java.net – for implementing networking apps
– java.sql – for accessing data in a data source
– and many more…
Class fields and class methods
• A class field is associated with the class in which
it is defined rather than with each instance of the
class.
– public static final double PI = 3.14159
• The static modifier says that the field is a class
field.
• The final modifier indicates that the value in the
field does not change ie a constant
Using Math Class
• All methods of the Math class are class
methods
• Must use the class name to invoke the methods
– Math.round(x), Math.pow(x,y), Math.sqrt(y)
– …
• A utility type class
• A class field is associated with the class in
which it is defined rather than with each
instance of the class
Class fields and class methods
• A class field is associated with the class in
which it is defined rather than with each
instance of the class.
– public static final double PI = 3.14159
• The static modifier says that the field is a
class field.
• The final modifier indicates that the value in
the field does not change ie a constant
Class fields and class methods
• A class methods are declared with the static
modifier, they are associated with the class,
rather than the instance.
Public static double radinsToDegrees(double rads)
{ return rads *180/PI;}
System.out.println(c+"\t"+ Math.round(c*9.0/5 + 32));
• A class method can use any class fields and
other class methods of its own class.
static Methods in Class Math
• static method (or class method)
– Applies to the class as a whole instead of a specific
object of the class
– Call a static method by using the method call:
ClassName.methodName( arguments )
– All methods of the Math class are static
• example: Math.sqrt( 900.0 )
TemperatureTable
class TemperatureTable {
TemperatureTable() {
System.out.println("Temperature Conversion Table");
System.out.println("============================");
System.out.println();
System.out.println("C\tF");
for (int c = 5; c <= 20; c++) {
System.out.println(c+"\t"+ Math.round(c*9.0/5 + 32));
}
}
public static void main ( String[] args) {
new TemperatureTable ();
}
}
static Fields and Class Math
• Constants
– Keyword final
– Cannot be changed after initialization
• static fields (or class variables)
– Are fields where one copy of the variable is shared
among all objects of the class
• Math.PI and Math.E are final static fields of the
Math class
Math class methods.
Method
Description
Example
abs( x )
absolute value of x
ceil( x )
rounds x to the smallest integer not
less than x
abs( 0.0 ) is 0.0
abs( -23.7 ) is 23.7
ceil( 9.2 ) is 10.0
ceil( -9.8 ) is -9.0
cos( x )
trigonometric cosine of x (x in radians)
cos( 0.0 ) is 1.0
exp( x )
exponential method ex
floor( x )
rounds x to the largest integer not greater Floor( 9.2 ) is 9.0
than x
floor( -9.8 ) is -10.0
log( x )
natural logarithm of x (base e)
abs( 23.7 ) is 23.7
max( x, y ) larger value of x and y
min( x, y ) smaller value of x and y
exp( 1.0 ) is 2.71828
exp( 2.0 ) is 7.38906
log( Math.E ) is 1.0
log( Math.E * Math.E ) is 2.0
max( 2.3, 12.7 ) is 12.7
max( -2.3, -12.7 ) is -2.3
min( 2.3, 12.7 ) is 2.3
min( -2.3, -12.7 ) is -12.7
pow( x, y ) x raised to the power y (i.e., xy)
pow( 2.0, 7.0 ) is 128.0
pow( 9.0, 0.5 ) is 3.0
sin( x )
trigonometric sine of x (x in radians)
sin( 0.0 ) is 0.0
sqrt( x )
square root of x
sqrt( 900.0 ) is 30.0
tan( x )
trigonometric tangent of x (x in radians)
tan( 0.0 ) is 0.0
static Method main
• Method main
– main is declared static so it can be invoked without
creating an object of the class containing main
– Any class can contain a main method
• The JVM invokes the main method belonging to
the class specified by the first command-line
argument to the java command
Account example
• Account class
– Interest rate – have the same interest rate for all accounts
– Declare it as a class field / attribute
public class Account {
private int accountno;
private String name;
private String address;
private double balance;
static double interestrate = 3.5; //class field
static void changeRate(double rate){
interestrate = rate;}
// class method
– To change the interest rate , we need to create a class
method to update it.
Account example
• AccountTest class
– To change the interest rate , we use the class method .
– Use the Class name . Class method name
Account.changeRate(4.5); //class method
• How would you update the account class to automatically allocate
a new
account number for each account created.
Examples of Vectors
• import java.io.*;
• import java.util.*;
• class VectorApp{ public static void
main(String[] args){
• Vector v = new Vector(20);
• Integer j = null;
• int i;
•
System.out.println("Generating random integers between 1 and 100, wrapping it as
integer objects and adding to a vector object");
•
for(i=0;i<10;i++){
•
j = new Integer((int)(Math.random() * 100)); v.addElement(j);
•
System.out.println("Added Integer object elements " + j);
•
}
•
System.out.println("size of the vector "+v.size()); System.out.println("capacity of the
vector "+v.capacity()); Enumeration enum = v.elements();
•
while(enum.hasMoreElements())
•
System.out.println("Enumeration of the elements in the vector container
"+(Integer)enum.nextElement());
•
System.out.println("");
•
}
•
}