Java 'The Next Generation'

Tuesday 28 February 2012

Fibonacci numbers (Right side)

import java.text.*;

public class TestRight {
public static void main(String args[]) {
long f1 = 1;
long f2 = 1;
RightFormat rf = new RightFormat(20);

System.out.println("Test of RightFormat(20) on Fibonacci numbers:");
for(int ix = 0; ix < 32; ix++) {
System.out.println(rf.format(Long.toString(f1)));
System.out.println(rf.format(Long.toString(f2)));
f1 = f1 + f2;
f2 = f2 + f1;
}
}
}

Empty Directory

import java.io.*;
//DANGEROUS Program to empty a directory

public class Empty {
public static void main(String[] argv) {
if (argv.length != 1) { // no progname in argv[0]
System.err.println("usage: Empty dirname");
System.exit(1);
}

File dir = new File(argv[0]);
if (!dir.exists()) {
System.out.println(argv[0] + " does not exist");
return;
}

String[] info = dir.list();
for (int i=0; i File n = new File(argv[0] + dir.separator + info[i]);
if (!n.isFile()) // skip ., .., other directories too
continue;
System.out.println("removing " + n.getPath());
if (!n.delete())
System.err.println("Couldn't remove " + n.getPath());
}
}
}

Double Array

// Double-subscripted array example
import java.awt.*;
import javax.swing.*;

public class DoubleArray extends JApplet
{
int grades[][] = { { 77, 68, 86, 73 }, { 96, 87, 89, 81 }, { 70, 90, 86, 81 } };

int students, exams;
String output;
JTextArea outputArea;

// initialize instance variables
public void init()
{
students = grades.length;
exams = grades[ 0 ].length;

outputArea = new JTextArea();
Container c = getContentPane();
c.add( outputArea );

// build the output string
output = "The array is:\n";
buildString();

output += "\n\nLowest grade: " + minimum() +
"\nHighest grade: " + maximum() + "\n";

for ( int i = 0; i < students; i++ )
output += "\nAverage for student " + i + " is " + average( grades[ i ] );

outputArea.setFont( new Font( "Courier", Font.PLAIN, 12 ) );
outputArea.setText( output );
}

// find the minimum grade
public int minimum()
{
int lowGrade = 100;

for ( int i = 0; i < students; i++ )
for ( int j = 0; j < exams; j++ )
if ( grades[ i ][ j ] < lowGrade )
lowGrade = grades[ i ][ j ];

return lowGrade;
}


// find the maximum grade
public int maximum()
{
int highGrade = 0;

for ( int i = 0; i < students; i++ )
for ( int j = 0; j < exams; j++ )
if ( grades[ i ][ j ] > highGrade )
highGrade = grades[ i ][ j ];

return highGrade;
}

// determine the average grade for a particular
// student (or set of grades)
public double average( int setOfGrades[] )
{
int total = 0;

for ( int i = 0; i < setOfGrades.length; i++ )
total += setOfGrades[ i ];

return ( double ) total / setOfGrades.length;
}

// build output string
public void buildString()
{
output += " "; // used to align column heads

for ( int i = 0; i < exams; i++ )
output += "[" + i + "] ";

for ( int i = 0; i < students; i++ )
{
output += "\ngrades[" + i + "] ";

for ( int j = 0; j < exams; j++ )
output += grades[ i ][ j ] + " ";
}
}
}

DOS Calculator

public class Calculator {
public static abstract class Operation {
private final String name;

Operation(String name) { this.name = name; }

public String toString() { return this.name; }

// Perform arithmetic op represented by this constant
abstract double eval(double x, double y);

// Doubly nested anonymous classes
public static final Operation PLUS = new Operation("+") {
double eval(double x, double y) { return x + y; }
};
public static final Operation MINUS = new Operation("-") {
double eval(double x, double y) { return x - y; }
};
public static final Operation TIMES = new Operation("*") {
double eval(double x, double y) { return x * y; }
};
public static final Operation DIVIDE = new Operation("/") {
double eval(double x, double y) { return x / y; }
};
}

// Return the results of the specified calculation
public double calculate(double x, Operation op, double y) {
return op.eval(x, y);
}
}

public class CalcTest {
public static void main(String args[]) {
double x = Double.parseDouble(args[0]);
double y = Double.parseDouble(args[1]);

operate(x, Calculator.Operation.PLUS, y);
operate(x, Calculator.Operation.MINUS, y);
operate(x, Calculator.Operation.TIMES, y);
operate(x, Calculator.Operation.DIVIDE, y);
}

static void operate(double x, Calculator.Operation op, double y) {
Calculator c = new Calculator();
System.out.println(x + " " + op + " " + y + " = " +
c.calculate(x, op, y));
}
}

Demonstrating the logical operators

import javax.swing.*;

public class LogicalOperators
{
public static void main( String args[] )
{
JTextArea outputArea = new JTextArea( 17, 20 );
JScrollPane scroller = new JScrollPane( outputArea );
String output = "";

output += "Logical AND (&&)" +
"\nfalse && false: " + ( false && false ) +
"\nfalse && true: " + ( false && true ) +
"\ntrue && false: " + ( true && false ) +
"\ntrue && true: " + ( true && true );

output += "\n\nLogical OR (||)" +
"\nfalse || false: " + ( false || false ) +
"\nfalse || true: " + ( false || true ) +
"\ntrue || false: " + ( true || false ) +
"\ntrue || true: " + ( true || true );

output += "\n\nBoolean logical AND (&)" +
"\nfalse & false: " + ( false & false ) +
"\nfalse & true: " + ( false & true ) +
"\ntrue & false: " + ( true & false ) +
"\ntrue & true: " + ( true & true );

output += "\n\nBoolean logical inclusive OR (|)" +
"\nfalse | false: " + ( false | false ) +
"\nfalse | true: " + ( false | true ) +
"\ntrue | false: " + ( true | false ) +
"\ntrue | true: " + ( true | true );

output += "\n\nBoolean logical exclusive OR (^)" +
"\nfalse ^ false: " + ( false ^ false ) +
"\nfalse ^ true: " + ( false ^ true ) +
"\ntrue ^ false: " + ( true ^ false ) +
"\ntrue ^ true: " + ( true ^ true );

output += "\n\nLogical NOT (!)" +
"\n!false: " + ( !false ) +
"\n!true: " + ( !true );

outputArea.setText( output );
JOptionPane.showMessageDialog( null, scroller, "Truth Tables", JOptionPane.INFORMATION_MESSAGE );
System.exit( 0 );
}
}

Demonstrating the logical operators

Demonstrating the File class

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;

public class FileTest extends JFrame implements ActionListener
{
private JTextField enter;
private JTextArea output;
public FileTest()
{
super( "Testing class File" );

enter = new JTextField( "Enter file or directory name here" );
enter.addActionListener( this );
output = new JTextArea();
Container c = getContentPane();
ScrollPane p = new ScrollPane();
p.add( output );
c.add( enter, BorderLayout.NORTH );
c.add( p, BorderLayout.CENTER );

setSize( 400, 400 );
show();
}

public void actionPerformed( ActionEvent e )
{
File name = new File( e.getActionCommand() );

if ( name.exists() )
{
output.setText( name.getName() + " exists\n" + ( name.isFile() ? "is a file\n" :
"is not a file\n" ) +
( name.isDirectory() ? "is a directory\n" :
"is not a directory\n" ) +
( name.isAbsolute() ? "is absolute path\n" :
"is not absolute path\n" ) +
"Last modified: " + name.lastModified() +
"\nLength: " + name.length() +
"\nPath: " + name.getPath() +
"\nAbsolute path: " + name.getAbsolutePath() +
"\nParent: " + name.getParent() );

if ( name.isFile() )
{
try
{
RandomAccessFile r = new RandomAccessFile( name, "r" );
StringBuffer buf = new StringBuffer();
String text;
output.append( "\n\n" );

while( ( text = r.readLine() ) != null )
buf.append( text + "\n" );

output.append( buf.toString() );
}
catch( IOException e2 )
{
JOptionPane.showMessageDialog( this, "FILE ERROR",
"FILE ERROR", JOptionPane.ERROR_MESSAGE );
}
}
else if ( name.isDirectory() )
{
String directory[] = name.list();

output.append( "\n\nDirectory contents:\n");

for ( int i = 0; i < directory.length; i++ )
output.append( directory[ i ] + "\n" );
}
}
else
{
JOptionPane.showMessageDialog( this, e.getActionCommand() + " Does Not Exist",
"FILE ERROR", JOptionPane.ERROR_MESSAGE );
}
}

public static void main( String args[] )
{
FileTest app = new FileTest();

app.addWindowListener( new WindowAdapter()
{
public void windowClosing( WindowEvent e )
{
System.exit( 0 );
}
} );
}
}