[JAVA] Posso compilare ed eseguire questa applet fuori dal browser?

[Matrixbob]

Transmission versus Propagation Delay (http://media.pearsoncmg.com/aw/aw_kurose_network_2/applets/transmission/delay.html)


///////////////////////////////////////
//LineSimApllet
//written by David Grangier, Institut Eurecom, France
//david.grangier@eurecom.fr
///////////////////////////////////////

package linesim;
//imports
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.applet.*;
import java.util.*;

//Applet Class
public class LineSimApplet extends Applet {
//buttons
Button start=new Button ("Start");
Button stop=new Button ("Reset");
//features lists
MyChoice length=new MyChoice(new String[] {"10 km","100 km","1000 km"},new double[] {10E3,100E3,1E6},3);
MyChoice rate=new MyChoice(new String[] {"512 kps","1 Mbps","10 Mbps","100 Mbps"},new double[] {512E3,1E6,10E6,100E6},2);
MyChoice size=new MyChoice(new String[] {"100 Bytes","500 Bytes","1 kBytes"},new double[] {8E2,4E3,8E3},1);
//to simulate time
Thread timerThread;
TickTask timerTask;
boolean simulationRunning=false;
//communication line
Line myLine;

public void init() {
try {
setBackground(Color.white);
add(new Label ("Length",Label.RIGHT));
add(length);
add(new Label("Rate",Label.RIGHT));
add(rate);
add(new Label("Packet size",Label.RIGHT));
add(size);
//start
start.addActionListener(
new ActionListener()
{
public void actionPerformed (ActionEvent event)
{
launchSim();
}
});
add(start);
//stop
Button stop=new Button ("Reset");
stop.addActionListener(
new ActionListener()
{
public void actionPerformed (ActionEvent event)
{
stopSim();
//clear line
myLine.sendTime(0);
//redraw cleared line
LineSimApplet.this.repaint();
}
});
add(stop);
//line
myLine= new Line(40,50,450,10);
}
catch(Exception e) {
e.printStackTrace();
}
}

public void paint (Graphics g)
{
update(g); // eliminate flashing : update is overriden
}

public void update (Graphics g)
{ //work on a offscreen image

Dimension offDimension = getSize();
Image offImage = createImage(offDimension.width, offDimension.height);
Graphics offGraphics = offImage.getGraphics();
myLine.drawLine(offGraphics);

//sender
offGraphics.setColor(Color.blue);
offGraphics.fillRect(10,40,30,30);
offGraphics.setColor(Color.black);
offGraphics.drawString("Sender",5,90);
offGraphics.drawRect(10,40,30,30);

//receiver
offGraphics.setColor(Color.blue);
offGraphics.fillRect(490,40,30,30);
offGraphics.setColor(Color.black);
offGraphics.drawString("Receiver",485,90);
offGraphics.drawRect(490,40,30,30);

offGraphics.drawString("Propagation speed : 2.8 x 10^8 m/sec",175,105);
//display offscreen image
g.drawImage(offImage, 0, 0, this);
}

private void launchSim()
{
setupEnabled(false);
//setup line
myLine.setup(length.getVal(), rate.getVal() );
myLine.emitPacket(size.getVal(),0);
//setup timer
timerTask=new TickTask(1E-5,myLine.totalTime());
timerThread=new Thread(timerTask);
//start simulation
simulationRunning=true;
timerThread.start();
}

private void stopSim()
{
timerTask.endNow();
simulationRunning=false;
setupEnabled(true);
}

public void setupEnabled(boolean value)
{
start.setEnabled(value);
length.setEnabled(value);
rate.setEnabled(value);
size.setEnabled(value);
}

//my choice
class MyChoice extends Choice
{
private double vals[];

public MyChoice(String items[], double values[],int defaultValue)
{
for (int i=0; i<items.length;i++) {super.addItem(items[i]);}
vals=values;
select(defaultValue-1);
}

public double getVal() {return vals[super.getSelectedIndex()];}
}
//tickTask
class TickTask implements Runnable
{
private double counter;
private double length;
private double tick;

public TickTask(double t,double l)
{
length=l;
tick=t;
counter=0;
}

public void run()
{
while (LineSimApplet.this.simulationRunning)
{
counter+=tick;
LineSimApplet.this.myLine.sendTime(counter);
LineSimApplet.this.repaint();
if (counter>=length)
{
LineSimApplet.this.myLine.clearPackets();
LineSimApplet.this.timerThread.suspend();
}
try {LineSimApplet.this.timerThread.sleep(50);} catch (Exception e) { }
}
}

public void endNow() {
length=counter;
}
}
}

//Line class
class Line
{
//graphic variables
private int gX;
private int gY;
private int gWidth;
private int gHeight;
//characteristic variables
final double celerity = 2.8E+8;
private double length;
private double rate;
//simulation variables
private double time;
private Packet myPacket;

public Line(int x, int y, int w, int h)
{
//graphic init
gX=x;
gY=y;
gWidth=w;
gHeight=h;
}

public void setup(double l, double r)
{
length=l;
rate=r;
}

void sendTime(double now)
{
time=now; //update time
removeReceivedPackets(now);
}

void emitPacket(double s, double eT)
{
myPacket= new Packet(s,eT);
}

private void removeReceivedPackets(double now)
{
if (!(myPacket==null))
{
if ( now>myPacket.emissionTime+(myPacket.size/rate)+length*celerity )
{
clearPackets();
}
}
}

public void clearPackets()
{
myPacket=null;
}

public double totalTime()
{
double emmissionTime=(myPacket.size/rate);
double onLineTime=(length/celerity);
return (emmissionTime+onLineTime);
}

public void drawLine(Graphics g)
{
g.setColor(Color.white);
g.fillRect(gX,gY+1,gWidth,gHeight-2);
g.setColor(Color.black);
g.drawRect(gX,gY,gWidth,gHeight);
g.setColor(Color.red);
g.drawString(timeToString(time),gX+gWidth/2-10,gY+gHeight+15);
drawPackets(g);
}

private void drawPackets(Graphics g)
{
if (!(myPacket==null))
{
double xfirst;
double xlast;
//compute time units
xfirst=time-myPacket.emissionTime;
xlast=xfirst-(myPacket.size/rate);
//compute position
xfirst=xfirst*celerity*gWidth/length;
xlast=xlast*celerity*gWidth/length;
if (xlast<0) {xlast=0;}
if (xfirst>gWidth ) {xfirst=gWidth;}
//draw
g.setColor(Color.red);
g.fillRect(gX+(int)(xlast),gY+1,(int)(xfirst-xlast),gHeight-2);
}
}

static private String timeToString(double now)
{
String res=Double.toString(now*1000);
int dot=res.indexOf('.');
String deci=res.substring(dot+1)+"000";
deci=deci.substring(0,3);
String inte=res.substring(0,dot);
return inte+"."+deci+" ms";
}
}

class Packet
{
double size;
double emissionTime;

Packet(double s, double eT)
{
size=s;
emissionTime=eT;
}
}

[Matrixbob]

Forse splittando le classi del file sorgente e usando AppletViewer (http://en.wikipedia.org/wiki/AppletViewer) potrei riuscire, dico questo perchè ho visto che manca un metodo d'ingresso main?

[Matrixbob]

up

[PGI-Bis]

L'applet in questione non usa i metodi di connessione al browser quindi puoi tranquillamente considerarlo come un qualsiasi componente awt, con l'unica particolarità del ciclo vitale. Vale a dire che se scrivi:

Applet applet = new LineSimApplet();
Frame frame = new Frame();
frame.add(applet);
applet.init();
applet.start();
frame.setSize(800, 600);
frame.setVisible(true);

Hai la tua applet in finestra. Un test completo apparentemente funzionante è:


import java.awt.*;
import java.awt.event.*;

public class Main {

public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {

public void run() {
final LineSimApplet applet = new LineSimApplet();
applet.init();
final Frame frame = new Frame("Wrapper");
frame.add(applet);
frame.addWindowListener(new WindowAdapter() {

public void windowOpened(WindowEvent e) {
applet.start();
}

public void windowClosing(WindowEvent e) {
applet.stop();
applet.destroy();
frame.dispose();
Thread killer = new Thread() {
public void run() {
try {
Thread.sleep(2000);
System.exit(0);
} catch(Exception ex) {}
}
};
killer.setDaemon(true);
killer.start();
}
});
frame.pack();
frame.setSize(frame.getWidth(), 600);
frame.setVisible(true);
}
});
}
}

[Matrixbob]

Mi da errore:

Main.java:10: cannot find symbol
symbol: class LineSimApplet
final LineSimApplet applet = new LineSimApplet();
^
Main.java:10: cannot find symbol
symbol: class LineSimApplet
final LineSimApplet applet = new LineSimApplet();
^
2 errors


Ma devo splittare tutte le classi ognuna in un file come JavaDoc insegna?
Dico questo perchè quel file che ho postato è un file omnicomprensivo.

[PGI-Bis]

50 frustate per l'uso del termine "splittare", ridotte a 25 per "omnicomprensivo".


Non è necessario separare i tipi top level dichiarati nell'unità di compilazione LineSimApplet.java - la lingua permette l'esistenza di più tipi top level nella stessa unità di compilazione purchè uno solo tra essi sia pubblico.

Aggiungi tra gli import di "Main.java":

import linesim.LineSimApplet

Oppure imposta il package di Main a "linesim". O rimuovi il package da LineSimApplet. Puoi anche impacchettare tutto in una sola unità di compilazione, senza package.


import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class Main {

public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {

public void run() {
final LineSimApplet applet = new LineSimApplet();
applet.init();
final Frame frame = new Frame("Wrapper");
frame.add(applet);
frame.addWindowListener(new WindowAdapter() {

public void windowOpened(WindowEvent e) {
applet.start();
}

public void windowClosing(WindowEvent e) {
applet.stop();
applet.destroy();
frame.dispose();
Thread killer = new Thread() {

public void run() {
try {
Thread.sleep(2000);
System.exit(0);
} catch (Exception ex) {
}
}
};
killer.setDaemon(true);
killer.start();
}
});
frame.pack();
frame.setSize(frame.getWidth(), 600);
frame.setVisible(true);
}
});
}
}

class LineSimApplet extends Applet {
//buttons

Button start = new Button("Start");
Button stop = new Button("Reset");
//features lists
MyChoice length = new MyChoice(new String[]{"10 km", "100 km", "1000 km"}, new double[]{10E3, 100E3, 1E6}, 3);
MyChoice rate = new MyChoice(new String[]{"512 kps", "1 Mbps", "10 Mbps", "100 Mbps"}, new double[]{512E3, 1E6, 10E6, 100E6}, 2);
MyChoice size = new MyChoice(new String[]{"100 Bytes", "500 Bytes", "1 kBytes"}, new double[]{8E2, 4E3, 8E3}, 1);
//to simulate time
Thread timerThread;
TickTask timerTask;
boolean simulationRunning = false;
//communication line
Line myLine;

public void init() {
try {
setBackground(Color.white);
add(new Label("Length", Label.RIGHT));
add(length);
add(new Label("Rate", Label.RIGHT));
add(rate);
add(new Label("Packet size", Label.RIGHT));
add(size);
//start
start.addActionListener(
new ActionListener() {

public void actionPerformed(ActionEvent event) {
launchSim();
}
});
add(start);
//stop
Button stop = new Button("Reset");
stop.addActionListener(
new ActionListener() {

public void actionPerformed(ActionEvent event) {
stopSim();
//clear line
myLine.sendTime(0);
//redraw cleared line
LineSimApplet.this.repaint();
}
});
add(stop);
//line
myLine = new Line(40, 50, 450, 10);
} catch (Exception e) {
e.printStackTrace();
}
}

public void paint(Graphics g) {
update(g); // eliminate flashing : update is overriden
}

public void update(Graphics g) { //work on a offscreen image

Dimension offDimension = getSize();
Image offImage = createImage(offDimension.width, offDimension.height);
Graphics offGraphics = offImage.getGraphics();
myLine.drawLine(offGraphics);

//sender
offGraphics.setColor(Color.blue);
offGraphics.fillRect(10, 40, 30, 30);
offGraphics.setColor(Color.black);
offGraphics.drawString("Sender", 5, 90);
offGraphics.drawRect(10, 40, 30, 30);

//receiver
offGraphics.setColor(Color.blue);
offGraphics.fillRect(490, 40, 30, 30);
offGraphics.setColor(Color.black);
offGraphics.drawString("Receiver", 485, 90);
offGraphics.drawRect(490, 40, 30, 30);

offGraphics.drawString("Propagation speed : 2.8 x 10^8 m/sec", 175, 105);
//display offscreen image
g.drawImage(offImage, 0, 0, this);
}

private void launchSim() {
setupEnabled(false);
//setup line
myLine.setup(length.getVal(), rate.getVal());
myLine.emitPacket(size.getVal(), 0);
//setup timer
timerTask = new TickTask(1E-5, myLine.totalTime());
timerThread = new Thread(timerTask);
//start simulation
simulationRunning = true;
timerThread.start();
}

private void stopSim() {
timerTask.endNow();
simulationRunning = false;
setupEnabled(true);
}

public void setupEnabled(boolean value) {
start.setEnabled(value);
length.setEnabled(value);
rate.setEnabled(value);
size.setEnabled(value);
}

//my choice
class MyChoice extends Choice {

private double vals[];

public MyChoice(String items[], double values[], int defaultValue) {
for (int i = 0; i < items.length; i++) {
super.addItem(items[i]);
}
vals = values;
select(defaultValue - 1);
}

public double getVal() {
return vals[super.getSelectedIndex()];
}
}
//tickTask

class TickTask implements Runnable {

private double counter;
private double length;
private double tick;

public TickTask(double t, double l) {
length = l;
tick = t;
counter = 0;
}

public void run() {
while (LineSimApplet.this.simulationRunning) {
counter += tick;
LineSimApplet.this.myLine.sendTime(counter);
LineSimApplet.this.repaint();
if (counter >= length) {
LineSimApplet.this.myLine.clearPackets();
LineSimApplet.this.timerThread.suspend();
}
try {
LineSimApplet.this.timerThread.sleep(50);
} catch (Exception e) {
}
}
}

public void endNow() {
length = counter;
}
}
}

//Line class
class Line {
//graphic variables

private int gX;
private int gY;
private int gWidth;
private int gHeight;
//characteristic variables
final double celerity = 2.8E+8;
private double length;
private double rate;
//simulation variables
private double time;
private Packet myPacket;

public Line(int x, int y, int w, int h) {
//graphic init
gX = x;
gY = y;
gWidth = w;
gHeight = h;
}

public void setup(double l, double r) {
length = l;
rate = r;
}

void sendTime(double now) {
time = now; //update time
removeReceivedPackets(now);
}

void emitPacket(double s, double eT) {
myPacket = new Packet(s, eT);
}

private void removeReceivedPackets(double now) {
if (!(myPacket == null)) {
if (now > myPacket.emissionTime + (myPacket.size / rate) + length * celerity) {
clearPackets();
}
}
}

public void clearPackets() {
myPacket = null;
}

public double totalTime() {
double emmissionTime = (myPacket.size / rate);
double onLineTime = (length / celerity);
return (emmissionTime + onLineTime);
}

public void drawLine(Graphics g) {
g.setColor(Color.white);
g.fillRect(gX, gY + 1, gWidth, gHeight - 2);
g.setColor(Color.black);
g.drawRect(gX, gY, gWidth, gHeight);
g.setColor(Color.red);
g.drawString(timeToString(time), gX + gWidth / 2 - 10, gY + gHeight + 15);
drawPackets(g);
}

private void drawPackets(Graphics g) {
if (!(myPacket == null)) {
double xfirst;
double xlast;
//compute time units
xfirst = time - myPacket.emissionTime;
xlast = xfirst - (myPacket.size / rate);
//compute position
xfirst = xfirst * celerity * gWidth / length;
xlast = xlast * celerity * gWidth / length;
if (xlast < 0) {
xlast = 0;
}
if (xfirst > gWidth) {
xfirst = gWidth;
}
//draw
g.setColor(Color.red);
g.fillRect(gX + (int) (xlast), gY + 1, (int) (xfirst - xlast), gHeight - 2);
}
}

static private String timeToString(double now) {
String res = Double.toString(now * 1000);
int dot = res.indexOf('.');
String deci = res.substring(dot + 1) + "000";
deci = deci.substring(0, 3);
String inte = res.substring(0, dot);
return inte + "." + deci + " ms";
}
}

class Packet {

double size;
double emissionTime;

Packet(double s, double eT) {
size = s;
emissionTime = eT;
}
}

Ovviamente al solo fine di provare il programma: in un contesto reale un sorgente del genere merita all'autore lo strappo delle unghie.

[Matrixbob]

edit: problemi di linea

[Matrixbob]

50 frustate per l'uso del termine "splittare", ridotte a 25 per "omnicomprensivo".


Non è necessario separare i tipi top level dichiarati nell'unità di compilazione LineSimApplet.java - la lingua permette l'esistenza di più tipi top level nella stessa unità di compilazione purchè uno solo tra essi sia pubblico.

Aggiungi tra gli import di "Main.java":

import linesim.LineSimApplet

Oppure imposta il package di Main a "linesim". O rimuovi il package da LineSimApplet. Puoi anche impacchettare tutto in una sola unità di compilazione, senza package.


package linesim;

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class UsaLineSim {

public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {

public void run() {
final LineSimApplet applet = new LineSimApplet();
applet.init();
final Frame frame = new Frame("Wrapper");
frame.add(applet);
frame.addWindowListener(new WindowAdapter() {

public void windowOpened(WindowEvent e) {
applet.start();
}

public void windowClosing(WindowEvent e) {
applet.stop();
applet.destroy();
frame.dispose();
Thread killer = new Thread() {

public void run() {
try {
Thread.sleep(2000);
System.exit(0);
} catch (Exception ex) {
}
}
};
killer.setDaemon(true);
killer.start();
}
});
frame.pack();
frame.setSize(frame.getWidth(), 600);
frame.setVisible(true);
}
});
}
}

class LineSimApplet extends Applet {
// buttons

/**
*
*/
private static final long serialVersionUID = 1L;
Button start = new Button("Start");
Button stop = new Button("Reset");
// features lists
MyChoice length = new MyChoice(
new String[] { "10 km", "100 km", "1000 km" }, new double[] { 10E3,
100E3, 1E6 }, 3);
MyChoice rate = new MyChoice(new String[] { "512 kps", "1 Mbps", "10 Mbps",
"100 Mbps" }, new double[] { 512E3, 1E6, 10E6, 100E6 }, 2);
MyChoice size = new MyChoice(new String[] { "100 Bytes", "500 Bytes",
"1 kBytes" }, new double[] { 8E2, 4E3, 8E3 }, 1);
// to simulate time
Thread timerThread;
TickTask timerTask;
boolean simulationRunning = false;
// communication line
Line myLine;

public void init() {
try {
setBackground(Color.white);
add(new Label("Length", Label.RIGHT));
add(length);
add(new Label("Rate", Label.RIGHT));
add(rate);
add(new Label("Packet size", Label.RIGHT));
add(size);
// start
start.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent event) {
launchSim();
}
});
add(start);
// stop
Button stop = new Button("Reset");
stop.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent event) {
stopSim();
// clear line
myLine.sendTime(0);
// redraw cleared line
LineSimApplet.this.repaint();
}
});
add(stop);
// line
myLine = new Line(40, 50, 450, 10);
} catch (Exception e) {
e.printStackTrace();
}
}

public void paint(Graphics g) {
update(g); // eliminate flashing : update is overriden
}

public void update(Graphics g) { // work on a offscreen image

Dimension offDimension = getSize();
Image offImage = createImage(offDimension.width, offDimension.height);
Graphics offGraphics = offImage.getGraphics();
myLine.drawLine(offGraphics);

// sender
offGraphics.setColor(Color.blue);
offGraphics.fillRect(10, 40, 30, 30);
offGraphics.setColor(Color.black);
offGraphics.drawString("Sender", 5, 90);
offGraphics.drawRect(10, 40, 30, 30);

// receiver
offGraphics.setColor(Color.blue);
offGraphics.fillRect(490, 40, 30, 30);
offGraphics.setColor(Color.black);
offGraphics.drawString("Receiver", 485, 90);
offGraphics.drawRect(490, 40, 30, 30);

offGraphics
.drawString("Propagation speed : 2.8 x 10^8 m/sec", 175, 105);
// display offscreen image
g.drawImage(offImage, 0, 0, this);
}

private void launchSim() {
setupEnabled(false);
// setup line
myLine.setup(length.getVal(), rate.getVal());
myLine.emitPacket(size.getVal(), 0);
// setup timer
timerTask = new TickTask(1E-5, myLine.totalTime());
timerThread = new Thread(timerTask);
// start simulation
simulationRunning = true;
timerThread.start();
}

private void stopSim() {
timerTask.endNow();
simulationRunning = false;
setupEnabled(true);
}

public void setupEnabled(boolean value) {
start.setEnabled(value);
length.setEnabled(value);
rate.setEnabled(value);
size.setEnabled(value);
}

// my choice
class MyChoice extends Choice {

/**
*
*/
private static final long serialVersionUID = 1L;
private double vals[];

public MyChoice(String items[], double values[], int defaultValue) {
for (int i = 0; i < items.length; i++) {
super.addItem(items[i]);
}
vals = values;
select(defaultValue - 1);
}

public double getVal() {
return vals[super.getSelectedIndex()];
}
}

// tickTask

class TickTask implements Runnable {

private double counter;
private double length;
private double tick;

public TickTask(double t, double l) {
length = l;
tick = t;
counter = 0;
}

@SuppressWarnings( { "deprecation", "static-access" })
public void run() {
while (LineSimApplet.this.simulationRunning) {
counter += tick;
LineSimApplet.this.myLine.sendTime(counter);
LineSimApplet.this.repaint();
if (counter >= length) {
LineSimApplet.this.myLine.clearPackets();
LineSimApplet.this.timerThread.suspend();
}
try {
LineSimApplet.this.timerThread.sleep(50);
} catch (Exception e) {
}
}
}

public void endNow() {
length = counter;
}
}
}

// Line class
class Line {
// graphic variables

private int gX;
private int gY;
private int gWidth;
private int gHeight;
// characteristic variables
final double celerity = 2.8E+8;
private double length;
private double rate;
// simulation variables
private double time;
private Packet myPacket;

public Line(int x, int y, int w, int h) {
// graphic init
gX = x;
gY = y;
gWidth = w;
gHeight = h;
}

public void setup(double l, double r) {
length = l;
rate = r;
}

void sendTime(double now) {
time = now; // update time
removeReceivedPackets(now);
}

void emitPacket(double s, double eT) {
myPacket = new Packet(s, eT);
}

private void removeReceivedPackets(double now) {
if (!(myPacket == null)) {
if (now > myPacket.emissionTime + (myPacket.size / rate) + length
* celerity) {
clearPackets();
}
}
}

public void clearPackets() {
myPacket = null;
}

public double totalTime() {
double emmissionTime = (myPacket.size / rate);
double onLineTime = (length / celerity);
return (emmissionTime + onLineTime);
}

public void drawLine(Graphics g) {
g.setColor(Color.white);
g.fillRect(gX, gY + 1, gWidth, gHeight - 2);
g.setColor(Color.black);
g.drawRect(gX, gY, gWidth, gHeight);
g.setColor(Color.red);
g.drawString(timeToString(time), gX + gWidth / 2 - 10, gY + gHeight
+ 15);
drawPackets(g);
}

private void drawPackets(Graphics g) {
if (!(myPacket == null)) {
double xfirst;
double xlast;
// compute time units
xfirst = time - myPacket.emissionTime;
xlast = xfirst - (myPacket.size / rate);
// compute position
xfirst = xfirst * celerity * gWidth / length;
xlast = xlast * celerity * gWidth / length;
if (xlast < 0) {
xlast = 0;
}
if (xfirst > gWidth) {
xfirst = gWidth;
}
// draw
g.setColor(Color.red);
g.fillRect(gX + (int) (xlast), gY + 1, (int) (xfirst - xlast),
gHeight - 2);
}
}

static private String timeToString(double now) {
String res = Double.toString(now * 1000);
int dot = res.indexOf('.');
String deci = res.substring(dot + 1) + "000";
deci = deci.substring(0, 3);
String inte = res.substring(0, dot);
return inte + "." + deci + " ms";
}
}

class Packet {

double size;
double emissionTime;

Packet(double s, double eT) {
size = s;
emissionTime = eT;
}
}


Ovviamente al solo fine di provare il programma: in un contesto reale un sorgente del genere merita all'autore lo strappo delle unghie.

Cavolo funziona!
Perchè meriterebbe lo strappo delle unghie il programmatore autore?

[PGI-Bis]

Lo strappo deriva da una violazione del bon-ton e da un problema di specifiche.

Convenzionalmente - e in java le convenzioni sono materia quasi religiosa - le unità di compilazione contengono sempre solo un tipo top-level (cioè una classe, interfaccia o enumerativo non contenuto in un altro tipo).

Il problema tecnico sta nella mancanza del package perchè le specifiche dichiarano che l'assenza di una dichiarazione di package rende il tipo dichiarato membro di un package liberamente decidibile dalla concreta implementazione della piattaforma java, non necessariamente sempre lo stesso. Sebbene l'implementazione di Sun-Oracle preveda un package ad hoc, che è sempre quello dal 1600 a.C., nulla vieta, ad esempio, che un'implementazione a fronte di due tipi aventi lo stesso nome appartenenti al package "innominato" vengano infilati in spazi dei nomi diversi.

In sostanza, quando omettiamo la dichiarazione di package facciamo affidamento ad una convenzione di un'implementazione di Java e non della piattaforma Java in senso stretto.

[Matrixbob]

Se vedi sopra ho modificato come mi consigliava Eclipse il codice.
Ma Java non vuole 1 classe 1 file scusa?
Come hai fatto a produrre quel main?

[PGI-Bis]

No, puoi dichiarare quanti tipi vuoi, purche uno solo tra quelli non contenuti in altri tipi sia pubblico. Cioè puoi tranquillamente dire:

//Pippo.java
class Giovannone {}

class Main {}

class Cocoricò {}

Oppure:

//Pippo.java
public class Pippo {}

class Giovannone {}
class Main {}
class Cocoricò {}

"Tranquillamente" dal punto di vista meccanico. Poi c'è la convenzione un file, un tipo con lo stesso nome del file, che è nel dna del programmatore java e viene sempre rispettata. Ma è una convenzione.