basic elements
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Tiberiu Leţia: Software Engineering –Java Programming Language – Programming Basic Elements 1
Java Language
Programming
Basic Programming Elements
Tiberiu Leţia: Software Engineering –Java Programming Language – Programming Basic Elements 2
Content
1. Stand alone applications and mini-applications
2. Name and identifiers
3. Java program structure
4. Data types
5. Operators
6. Flow execution control
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1. Stand alone applications and mini-applications
Mini- applications = applets
stand alone application)
= program that can be used independently.
They have main() method
public static void main (String[] args)
launching the execution (run program) Java interpreter
java numeProgram
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Applet
A Java program that extends Applet class.
This class doesn’t contain main method the program cannot be
launched using Java interpreter.
They are used in Web pages (via HTML file).
Web server
browser (ex. Internet Explorer, Mozilla Firefox).
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2. Names and Identifiers
An identifier is a sequence of unlimited length of letters and digits where
the first is compulsory a letter.
They are string of characters representing names given to variable, classes or
methods.
They should differ from keywords (including null, false and true).
Names are used for referring entities like packages, class types, interfaces,
type members, parameters, local variables etc.
The names can be:
simple - ex.: xxx
composed – sequences of identifiers separated by ".". ex.: xxx.yyy.zzz
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abstract do import public try
boolean double instanceof return void
break else int short volatile
byte extends interface static while
case final long super
catch finally native switch
char float new synchronized
class for null this
const goto package throw
continue if private throws
default implements protected transient
Keywords
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Ex.:
java.awt.BorderLayout
java.lang.System.out.println()
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3. Java Program Structure
Lexical entities:
comments –
keywords
identifiers
literals
separators – signs ({, }, [, ], ;, . and ,) used to separate lexical entities
operators
Variables
Constants
Expressions
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Instructions – lexical units that describe what the program has to
perform – the instructions are separated by ”;”.
Code block { instructions; }.
packages
subpackages
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Source files
Code source filename.java
Compiler javac filename.class
Package declaration:
package NumePachet;
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Program example: /** Program name
* Comments
*/
public class NumeClasaPrincipala
{
/**
* Metoda principala a aplicatiei *
* Se pot transmite parametrii prin tabelul de
argumente */
public static void main (String[] args)
{
// Aici se adauga codul programului
System.out.println("Salut! Merge programul!");
}//terminare metoda main
}
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Compilation javac
Running
java NumeClasaprincipala
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4. Data Types
Type variabileName;
Variable types in Java:
reference - classes, interfaces, arrays (or null) and
primitive data.
Where are they used?
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Primitive data types
Type Significance Dimension Minim Maxim
byte Integer 8 biţi -128 +127
short Integer cu semn 16 biţi -32768 32767
int Integer cu semn 32 biţi -2147483648 2147483648
long Integer cu semn 64 biţi -263 263-1
char Integer fără semn 16 biţi Characters Characters
float Float point
Virgulă mobilă în
simplă precizie
32 biţi -3.40282347*1038 3.40282347*1038
double Virgulă mobilă în
dublă precizie
64 biţi -
1.7976931348623157
0*10308
1.79769313486231
570*10308
boolean Val. booleană 32 biţi false true
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Data can be:
1. numerical - integers: byte, short, int, long, char;
2. numerical - real: float, double.
3. boolean - logical
4. character - char.
In Java are used for characters the standard Unicode (Wide Character) with
38.885 characters.
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String data1;
String data2=”sir de caractere”;
String data3=new String("alt sir");
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Data types declarations:
byte varByte; // variabila de 8 biti
short varShort; // variabila de 16 biti
int varInt; // variabila de 32 biti
long varLong; // variabila de 64 biti
long varLong=1L; //atribuire
long varLong=2l;
float varFloat; // variabila de 32 biti
double varDouble; // variabila de 64 biti
char caracter; // variabila de un caracter
char caracter = ‘c’; //declara variabila caracter
si ii atribuie //valoarea c
boolean val=true;
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Arrays:
int Matrice1[]; //
float Matrice2[][]; //
Matrice2 mat=new float[3][4];
int[] matrice3=new int[5];
mat şi matrice3 sunt date de tip referinţă (reference type).
String[] str= {"unu", "doi", "trei"};
int[] tab= {1, 3, 5, 2, 34};
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5. Operators
1. Assign operator - "=".
add (+=)
subtract (-=)
multiplication (*=)
divide (/=)
modulo (%=)
AND (&=)
OR (|=)
EXCLUSIVE OR (^=)
int x=y=z=25;
a = 3; // atribuie variabilei a valoarea 3
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a - = 5; // atribuie variabilei a rezultatul operaţiei a – 5. (scădere şi
atribuire)
a * = 2; // atribuie variabilei a rezultatul operaţiei a * 2. (înmulţire şi
atribuire)
a / = 5; // atribuie variabilei a rezultatul operaţiei a / 5
2. Binary arithmetic operators:
add (+) – ex.: a+b
subtract (-) – ex.: a-b
multiply (*) – ex.: a*b
divide (/) – ex.: a/b
modulo (%) – ex.: a%b
3. Unary arithmetic operators:
decrement (-) – ex.: a--
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increment (+) – ex.: a++
minus sign (-)
plus sign (+)
int x=3, y, z;
y=++x; // x este incrementat inainte de atribuire
z=y--; //intai se face atribuirea si apoi decrementarea
z=-y; //atribuie valoarea lui y cu semn schimbat
x=~y; //atribuie valoarea lui y cu complementare pe biti
float f1=3.15, f2;
f2=f1++;
f3=++f1;
f1=5.15, f2=3.15 şi f3=5.15.
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Order:
int < long < float < double
4. Relational operators:
equal (==)
different (!=)
greater (>)
smaller (<)
greater or equal (>=)
smaller or equal (<=)
type boolean (true or false).
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5. Logical operators:
- conditional – and – AND (&&)
or – OR (||)
- boolean - – NOT (!)
- AND (&)
- OR (|)
- XOR (^)
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6. Bit operators
Operator Operation Example
= Atribuire a = b
> Mai mare decât a > b
< Mai mic decât a < b
<= Mai mic sau egal cu a <= b
>= Mai mare sau egal cu a >= b
== Egal cu a == b
!= Nu este egal cu a != b
! Negaţie logică !a
~ Negaţie logică pe biţi ~a
?: Operatori condiţional a ? expr1 : expr2
&& ŞI (conditional AND) a && b
|| SAU (conditional OR) a || b
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++ Incrementare a++ or ++a
-- Decrementare a-- or --a
+ Adunare a + b
- Scădere a - b or -b
* Multiplicare a * b
/ Împărţire a / b
% Modulo a % b
& ŞI pe biţi (bitwise AND) a & b
| SAU pe biţi (bitwise OR) a | b
^ SAU EXCLUSIV pe biţi (XOR) a ^ b
<< Deplasare stânga a << b
>> Deplasare dreapta a >> b
>>> Deplasare dreapta cu umplere cu
zero
a >>> b
+= Atribuie rezultatul adunării a += b
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-= Atribuie rezultatul scăderii a -= b
*= Atribuie rezultatul înmulţirii a *= b
/= Atribuie rezultatul împărţirii a /= b
&= Atribuie rezultatul lui ŞI pe biţi a &= b
|= Atribuie rezultatul lui SAU pe biţi a |= b
^= Atribuie rezultatul lui SAU
EXCLUSIV pe biţi
a ^= b
%= Atribuie rezultatul lui modulo a %= b
<<= Atribuie rezultatul deplasării la
stânga
a <<= b
>>= Atribuie rezultatul deplasării la
dreapta
a >>= b
>>>= Atribuie rezultatul deplasării la
dreapta cu umplere cu zero
a >>>= b
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7. Concatenation operator for string of characters “+”.
String s1=”qwe”;
String s2=”M”;
String s3;
s3=s1+s2;
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6. Instructions for the control of execution
if,
for,
while,
do … while,
switch,
break and
continue.
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if instructions 1) if (expresie_conditie) instructiune;
2) if (expresie) {
instructiuni;
}
3) if (expresie) instructiune else instructiune;
4) if (expresie) {
instructiuni;
}
else
{
instructiuni;
}
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5) test ? rezultat_adevarat : rezultat_false;
z = (x < y) ? x : y;
if ((a==true) || (b==false)) { ....}
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switch
switch (test) {
case valoareUnu : rezultatUnu;
break:
case valoareDoi : rezultatDoi;
break;
case valoareTrei : rezultatTrei;
break;
…………..
default : rezultatImplicit;
}
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for loop
for (initialization; test; increment) instruction;
or
for (initialization; test; increment) {
instructions;
}
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for (int i=0; i<10; i++)
{
if (tab[i]==0)
{
System.out.println{“Eroare:Impartire cu zero”+ i);
break;
}
else tabel[i]=tabel[i]/tab[i];
}
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while and do … while
while (condition) {
corpulBuclei;
}
do {
corpulBuclei;
} while (condition);
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Example:
int contor=0;
while (contor < 10)
{
System.out.println(“In bucla: contor= “+ contor);
contor++;
}
int i=1;
do {
System.out.println(“In bucla: i= “+ i);
i++;
} while (i<=10);
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Instructions: break and continue
label_1: while () {
……………
if (…) break label_1;
continue;
………….
}//end while
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