Java

Java Language Programming
Basic Programming Elements

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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 argumente */ public static void main (String[] args) { // Aici se adauga codul programului System.out.println("Salut! Merge programul!"); }//terminare metoda main }

de

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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 byte short int long char Significance Integer Integer cu semn Integer cu semn Dimension Minim 8 biţi -128 16 biţi -32768 -2147483648 63 -2 Characters 38 -3.40282347*10 Maxim +127 32767 2147483648 63 2 -1 Characters 38 3.40282347*10

32 biţi Integer cu semn 64 biţi Integer fără semn 16 biţi Float point 32 biţi float Virgulă mobilă în simplă precizie double Virgulă mobilă în 64 biţi dublă precizie boolean Val. booleană 32 biţi

1.79769313486231 1.7976931348623157 570*10308 308 0*10 false true
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Tiberiu Leţia: Software Engineering –Java Programming Language – Programming Basic Elements

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-Tiberiu Leţia: Software Engineering –Java Programming Language – Programming Basic Elements
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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 (=)  smaller or equal ( < = == != ! ~ ?: && || Operation Atribuire Mai mare decât Mai mic decât Mai mic sau egal cu Mai mare sau egal cu Egal cu Nu este egal cu Negaţie logică Negaţie logică pe biţi Operatori condiţional ŞI (conditional AND) SAU (conditional OR) Example a=b a>b a >>> +=

Incrementare Decrementare Adunare Scădere Multiplicare Împărţire Modulo ŞI pe biţi (bitwise AND) SAU pe biţi (bitwise OR) SAU EXCLUSIV pe biţi (XOR) Deplasare stânga Deplasare dreapta Deplasare dreapta cu umplere cu zero Atribuie rezultatul adunării

a++ or ++a a-- or --a a+b a - b or -b a*b a/b a%b a&b a|b a^b a > b a >>> b a += b
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-= *= /= &= |= ^= %= = >>>=

Atribuie rezultatul scăderii Atribuie rezultatul înmulţirii Atribuie rezultatul împărţirii Atribuie rezultatul lui ŞI pe biţi Atribuie rezultatul lui SAU pe biţi Atribuie rezultatul lui SAU EXCLUSIV pe biţi Atribuie rezultatul lui modulo Atribuie rezultatul deplasării la stânga Atribuie rezultatul deplasării la dreapta Atribuie rezultatul deplasării la dreapta cu umplere cu zero

a -= b a *= b a /= b a &= b a |= b a ^= b a %= b a = b 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