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* Applicazione Java da linea di comando
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public class Esempio0 {
public static void main(String args[]){
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/** File Esempio0.java
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* che stampa la classica frase di benvenuto
*/
public class Esempio0 {
public static void main(String args[]){
System.out.println("Hello World!");
}
}
}
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* applicazione da linea di comando
* stampa gli argomenti passati al programma
*/
/** File Esempio2.java
* Prima applicazione che istanzia nuovi oggetti
*/
class Counter {
private int
public void
public void
public void
public int
}
public
class Esempio1 {
public static void main(String args[]){
if (args.length == 0)
System.out.println("Occorrono argomenti");
else
for(int i=0; i<args.length; i++)
System.out.println("arg" + (i+1) +
": " + args[i]);
}
}
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val;
reset()
inc()
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{
{
{
{
val = 0; }
val++; }
val--; }
return val; }
public class Esempio2 { // contiene solo il main
public static void main(String args[]){
Counter c1, c2;
c1 = new Counter(); c2 = new Counter();
c1.reset(); c2.reset();
c1.inc(); c1.inc(); c2.inc();
System.out.println("c1 vale " + c1.rd());
System.out.println("c2 vale " + c2.rd());
}
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class Counter {
private int val;
public Counter()
public Counter(int x)
public void reset() {
public void inc()
{
public void dec()
{
public int rd()
{
}
{ val=1; } // default
{ val=x; }
val = 0; }
val++; }
val--; }
return val; }
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/** FILE Counter.java
* Questa classe definisce il concetto di
contatore avanti/indietro.
*/
public class Counter {
private int val;
public Counter()
{
public Counter(int x)
public void reset() {
public void inc()
{
public void dec()
{
public int rd()
{
}
val=1; } // default
{ val=x; }
val = 0; }
val++; }
val--; }
return val; }
/** FILE Esempio2bis.java
* Prima applicazione che istanzia nuovi oggetti
*/
public class Esempio2bis {
public static void main(String args[]){
Counter c1, c2;
c1 = new Counter(); c2 = new Counter(5);
c1.inc(); c1.inc(); c2.inc();
System.out.println("c1 vale " + c1.rd());
System.out.println("c2 vale " + c2.rd());
}
}
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package pippo;
MDYDDZWSULQW%RRN
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public class Counter {
...
}
package pippo;
public class Esempio2bis {
public static void main(String args[]){
...
}
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/* classe definita nel package di default */
public class Esempio2ter {
public static void main(String args[]){
pippo.Counter c1, c2;
c1 = new pippo.Counter();
c2 = new pippo.Counter(5);
c1.inc(); c1.inc(); c2.inc();
... } }
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import pippo.Counter;
public class Esempio2ter {
public static void main(String args[]){
Counter c1, c2;
c1 = new Counter(); c2 = new Counter(5);
...
}
}
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/**
* verifica il concetto di clonazione di oggetti
*/
import java.awt.Point;
/**
* verifica il concetto di Riferimento a oggetti
*/
import java.awt.Point;
class Esempio3 { // contiene solo il main
public static void main(String args[]){
Point p1 = new Point(100,10), p2 = p1;
System.out.println("p1: " + p1.x + ","
System.out.println("p2: " + p2.x + ","
p1.x = 400;
System.out.println("p1: " + p1.x + ","
System.out.println("p2: " + p2.x + ","
}
}
class Esempio3bis {
public static void main(String args[]){
Point p1 = new Point(100,10), p2=p1;
System.out.println("p1: " + p1.x + "," + p1.y);
System.out.println("p2: " + p2.x + "," + p2.y);
p2 = (Point) p1.clone();
p1.x = 400;
System.out.println("p1: " + p1.x + "," + p1.y);
System.out.println("p2: " + p2.x + "," + p2.y);
+ p1.y);
+ p2.y);
}
}
+ p1.y);
+ p2.y);
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INTRODUZIONE ALLA OOP IN JAVA -- 17
INTRODUZIONE ALLA OOP IN JAVA -- 18
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/**
* verifica il concetto di uguaglianza fra oggetti
*/
import java.awt.Point;
class Esempio4 {
public static void main(String args[]){
Point p1 = new Point(100,10), p2=p1;
System.out.println("p1==p2? ” + (p1==p2));
System.out.println("p1.equals(p2)? ” +
p1.equals(p2));
p2 = (Point) p1.clone(); p1.x = 400;
System.out.println("p1==p2? ” + (p1==p2));
System.out.println("p1.equals(p2)? ” +
p1.equals(p2));
}
}
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p1.equals(p2)? true
p1==p2? false
p1.equals(p2)? false
INTRODUZIONE ALLA OOP IN JAVA -- 19
INTRODUZIONE ALLA OOP IN JAVA -- 20
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/**
*
Primo esempio d’uso di array in Java
*/
(6(03,2
/**
class
*
*/
Esempio5 {
public static void main(String args[]){
int[] v1 = {8,12,3,4};
// vettore di 4 int
int[] v2; // riferimento a un vettore di int
v2 = new int[5]; // creazione vett. di 5 int
// (crea 5 celle int, inizializzate a 0)
class
Esempio5bis {
static void main(String args[]){
public
String
Secondo esempio d’uso di array Java
//
for(int i=1; i<=v2.length; i++) v2[i-1] = i*i;
for(int i=0; i<v1.length; i++)
System.out.print(v1[i] + '\t');
System.out.println(“”);
for(int i=0; i<v2.length; i++)
System.out.print(v2[i] + '\t');
}
v1[]; // RIFERIMENTO al futuro vettore
si può anche scrivere String[] v1;
v1
= new String[2];
creazione vettore di due (rif. a) String
// NB: le due String però ancora non esistono!
//
v1[0]
= "Ciao mondo"; // una String costante
v1[1] = new String(v1[0]);
// una String creata din. uguale alla prima
}
}
}
INTRODUZIONE ALLA OOP IN JAVA -- 21
INTRODUZIONE ALLA OOP IN JAVA -- 22
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class Esempio6 {
public static void main(String args[]){
int x = 35;
// tipo primitivo
Integer ix = new Integer(x);
// conversione int Integer per costruzione
System.out.println("ix = " + ix);
// conversione implicita Integer String
x = ix.intValue()*4;
// conversione esplicita Integer int
System.out.println("x = " + x);
// conversione implicita int String
} }
INTRODUZIONE ALLA OOP IN JAVA -- 23
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class Counter {
private int val;
public Counter()
{
public Counter(int x)
public void reset() {
public void inc()
{
public void dec()
{
public int rd()
{
}
val=1; }
{ val=x; }
val = 0; }
val++; }
val--; }
return val; }
public class Esempio2bis {
public static void main(String args[]){
Counter c1, c2;
c1 = new Counter(); c2 = new Counter(5);
c1.inc(); c1.inc(); c2.dec();
System.out.println("c1 vale " + c1.rd());
System.out.println("c2 vale " + c2.rd());
}
}
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INTRODUZIONE ALLA OOP IN JAVA -- 24
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class Esempio7 {
static int[] creaIntervallo(int inf, int sup){
// restituisce un (rif. a) un array di int
int[] v = new int[sup-inf+1];
for (int i=0; i<v.length; i++) v[i]=inf++;
return v;
}
static void print(int v[]){
for(int i=0; i<v.length; i++)
System.out.println(v[i]);
}
static void increment(int v[]){
for(int i=0; i<v.length; i++) v[i]++;
}
public static void main(String args[]){
int[] v1 = creaIntervallo(3,8);
print(v1);
// Esempio7.print(v1);
increment(v1);
// Esempio7.increment(v1);
print(v1);
// Esempio7.print(v1);
}
}
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INTRODUZIONE ALLA OOP IN JAVA -- 25
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class Esempio7ter {
static int x = 8;
// variabile di classe
public static void main(String args[]){
x--;
// OK (visib. package)
// Sintassi completa: Esempio7ter.x--;
}
}
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INTRODUZIONE ALLA OOP IN JAVA -- 26
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class Esempio7quater {
public static final int mymax = 8;
// costante pubblica (di classe)
}
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class Esempio7quater {
static final int mymax = 8;
// costante a uso interno (di classe)
void metodo(){
final float radiceDi2 = 1.4142;
}
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class Counter {
private int val;
public Counter()
{ this(1); }
public Counter(int val) { this.val=val; }
public void reset() { val = 0; }
public void inc()
{ val++; }
public void dec()
{ val--; }
public int rd()
{ return val; }
}
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INTRODUZIONE ALLA OOP IN JAVA -- 27
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class Counter {
int val;
public Counter()
{ val=1; }
public Counter(int c) { val=c; }
public void inc()
{ val++; }
public int rd()
{ return val; }
}
public class Esempio {
Counter c;
(6(03,2GD&RXQWHUEDVHD&RXQWHUFRQGHFUHPHQWR
class Counter2 {
Counter c;
public Counter2()
{c = new Counter(); }
public Counter2(int v) {c = new Counter(v);}
public void inc()
{ c.inc(); }
public int rd()
{ return c.rd(); }
public void dec()
{ c.val--; }
}
// oggetto contenitore
// oggetto contenuto
public Esempio() { //costruttore di Esempio
c = new Counter(3);
}
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public static void main(String args){
Esempio e = new Esempio();
}
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}
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}
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public void dec()
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double val;
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Persona {
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Persona() { nome = "sconosciuto"; anni = 0; }
Persona(String n) { nome = n; anni = 0; }
Persona(String n, int a) { nome=n; anni=a; }
void print(){
System.out.print("Il mio nome e’ " + nome);
System.out.println(" e ho " + anni + " anni");
} }
/**
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Studente extends Persona {
int matr;
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Studente(String n, int a) { super(n,a); matr=7;}
Studente(String n, int a, int m) {
super(n,a); matr=m; }
void print(){ super.print();
System.out.println("Matricola = " + matr); }
}
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public class Esempio2 {
public static void main(String args[]){
Studente studente;
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studente = new Studente("Laura", 20, 1234);
studente.print();
} }
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class Esempio3 {
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Studente s = new Studente(“Tom”);
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s.print();
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}
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public static void main(String args[]){
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}
}
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import java.io.*;
class EsempioIn {
public static void main(String args[]){
int a = 0, b = 0;
BufferedReader in = new BufferedReader(
new InputStreamReader(System.in));
try { System.out.print("Primo valore: ");
a = Integer.parseInt(in.readLine());
System.out.print("Secondo valore:");
b = Integer.parseInt(in.readLine());}
catch (IOException e) {
System.out.println("Errore in input");
}
System.out.println("La somma vale " + (a+b));
} }
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