//This is the source code for a typical application applet written for the project

//"Software Supplement to Abstract Algebra " by Arvind Rajagopal, Univ. of Minn. Duluth.

import java.applet.Applet;

import java.awt.*;

import java.lang.*;

import algebra.*; //algebra package has the most important classes

import misc.*; //misc package has other miscellaneous classes

public class chap2q1Applet extends Applet {

textfield tf;
Button clearTextArea;
ScrollableCanvas can;
GridBagLayout gridbag = new GridBagLayout();
public void init() {
//The colors are accepted as applet parameters so that they can be changed
//as we please.
Color comp_background = getColorParameter(getParameter("cbg"));
Color applet_background = getColorParameter(getParameter("abg"));
Color comp_foreground = getColorParameter(getParameter("cfg"));
String f = "fname";
int st = Font.BOLD + Font.ITALIC;
int it = Font.ITALIC+Font.BOLD;
//The Font size is also accepted as an applet parameter.
int siz = Integer.parseInt( getParameter( "font_size" ) );
Font fon = new Font(f,st,siz);//This is the font we use for the text in the canvas.
Font italic = new Font("italic", it,siz);
this.setBackground(applet_background);
//The clear button.
clearTextArea = new Button("clear");
clearTextArea.setForeground(comp_foreground);
clearTextArea.setBackground(comp_background);
clearTextArea.setFont(fon);
//The textfield.
tf = new textfield(5);
tf.setForeground(comp_foreground);
tf.setBackground(comp_background);
tf.setFont(fon);
//Add Components to the Applet.
Label L = new Label("Enter n here:");
L.setForeground(comp_foreground);
L.setFont(italic); can = new ScrollableCanvas(375,150);
can.setForeground(comp_foreground);
can.setBackground(comp_background);
can.setFont(fon); this.setLayout(gridbag);
this.setFont(fon);
//The class misc.layout is used.
layout.constrain(this, L, 0,0,1,1);
layout.constrain(this, tf, GridBagConstraints.RELATIVE,
GridBagConstraints.RELATIVE,1,1, GridBagConstraints.HORIZONTAL,
GridBagConstraints.WEST, 0.0,0.0,0,0,0,0);
layout.constrain(this, can, 0,1,2,1, GridBagConstraints.HORIZONTAL,
GridBagConstraints.CENTER, 0.0,0.0,0,0,0,0);
layout.constrain(this, clearTextArea, 0,2, 2,1, GridBagConstraints.NONE,
GridBagConstraints.CENTER, 0.0,0.0,0,0,0,0 );
validate(); }
//*********end of init
//This method extracts the Colors which are passed as applet parameters.
//This method was taken from the book Java in a Nut Shell, 1st edn. O'Reilly Assoc.
protected Color getColorParameter(String name) {
String value = name;
int initvalue;
try {initvalue = Integer.parseInt(value,16);}
catch (NumberFormatException e) {return null;}
return new Color(initvalue);
}
public boolean action(Event event, Object obj) {
//Here we instantiate an object of type utilc2q1, which is an utility class specific
//for this application applet.
utilc2q1 utils = new utilc2q1();
switch(event.id) {
case Event.ACTION_EVENT:
if(event.target == tf) {
try{
String text = tf.getText();
int value = Integer.parseInt(text);
utils.ugroup(this.getGraphics(), value,can);
can.newanswer();
}
catch( NumberFormatException e ){
//This checks the user's entry and prints an error message if it is wrong.
sentence err = new sentence();
err.add( new specialString( "Error: Please check if you have "+
"entered an integer or given any " +
"space while entering. ", this.getFont()));
can.paint( err ); can.newanswer();
} tf.selectAll();
}//end of if
else if(event.target == clearTextArea) {
//If the clear button is pressed, the clear() method in the
//misc.ScrollableCanvas is called.
can.clear();
}
break;
default: break;
} //end of switch statement.
return true; }//************end of action

}//*************end of applet

//This class has all the utility functions for this application program.

class utilc2q1 {

public utilc2q1() {}
public void ugroup( Graphics g,int n, ScrollableCanvas canvas) {
int i,j;
//This sentence is used again and again.
sentence curr_sent = new sentence();
if(n <= 1) {
//Typically, this is how a sentence is sent for printing.
//First the individual strings are added to the sentence.
//then the paint(entity ent) of the misc.ScrollableCanvas is invoked.
///The current sentence is cleared for reuse
curr_sent.add( new specialString( String.valueOf(n) + " is not a valid number ",
g.getFont() ) );
canvas.paint(curr_sent);
curr_sent.erase();
return;
}//end of if
//Here we do the computations.
String heading = " a. The elements of U(" + String.valueOf(n) + ") are:" ;
curr_sent.add( new specialString( heading, g.getFont() ) );
canvas.paint(curr_sent);
curr_sent.erase();
String elements = " { 1 ";
for(i = 2; i < n; i++) {
if( Utilities.gcd(n,i) == 1 ) elements += String.valueOf( i ) + " ";
} elements += "}.";
curr_sent.add( new specialString( elements, g.getFont() ) );
canvas.paint(curr_sent);
curr_sent.erase();
curr_sent.add( new specialString( " b. The inverses of each member:" , g.getFont() ) ) ;
canvas.paint( curr_sent );
curr_sent.erase();
curr_sent.add( new specialString( " inverse of 1 is: 1 ", g.getFont() ) );
canvas.paint( curr_sent );
curr_sent.erase();
for(i = 2 ; i < n ; i++) {
if ( Utilities.gcd(n,i) == 1 ) {
for(j = 2 ; j < n ; j++) {
if( ( (i*j) %n) == 1 ) {
String temp = " inverse of " + String.valueOf(i) + " is: " +
String.valueOf(j) ;
curr_sent.add( new specialString( temp, g.getFont() ) );
canvas.paint(curr_sent);
curr_sent.erase();
} //end of if
} //end of for( j = 2... )
} //end of if
} //end of for(i = 2 ...... )
} //end of the method ugroup

}//**************end of utility************

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