Java util

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VECTORI
In limbajul Java vectorii sunt obiecte. Exista doua feluri de vectori :
• cu numar fix de elemente
• cu numar variabil de elemente
In primul caz nu exista un nume de clasa care se instantiaza pentru a obtine un obiect vector, in timp ce in al doilea caz este vorba de clasa Vector (java.util.Vector).

Vectori cu numar fix de elemente
Declaratii:
int v[];
int []v;
int [][]m;
int m[][];
Crearea :
v = new int[10];
m = new int[3][10];
int []factorial = {1, 1, 2, 6, 24, 120};
In Java nu exista vectori multidimensionali ci vectori de vectori. întâiul element dintr-un vector are indicele 0.
Cu ajutorul cuvantului cheie length se poate afla dimeniunea unui vector.
int [][]a = new int[5][10];
a.length  5
a[0].length  10
Copierea unui vector in alt vector se face cu susținerea metodei System.arraycopy:
int x[] = {1, 2, 3, 4};
int y[] = new int[4];
System.arraycopy(x,0,y,0,x.length);

Vectori cu numar variabil de elemente java util Vector
Implementarea vectorilor cu numar variabil de elemente este oferita de clasa Vector din pachetul java.util.
Un obiect de tip Vector contine numai elemente de tip Object.
Fiecare instanta a clasei Vector este caracterizata de 3 proprietati:
• tăria : nr. mare de elemente
• dimeniunea : nr. curent de elemente
• incrementul : cu cat creste posibilitatea in timpul in care mărimea = cpacitatea si se doreste adaugarea unui element nou in vector.

Variabile
capacityIncrement The size of the increment.
elementCount The number of elements in the buffer.
elementData The buffer where elements are stored.
Constructori
Vector (int, int)
Constructs an empty vector with the specified storage capacity and the specified capacityIncrement.
Vector(int) Constructs an empty vector with the specified storage capacity.
Vector() Constructs an empty vector.

Metode
addElement (Object) Adds the specified object as the last element of the vector.
capacity() Returns the current capacity of the vector.
clone() Returns a clone of the vector
contains(Object) Returns true if the specified object is a value of the collection.
copyInto(Object[]) Copies the elements of this vector into the specified array.
elementAt(int) Returns the element at the specified index.
elements() Returns an enumeration of the elements.
ensureCapacity(int) Ensures that the vector has at least the specified capacity.
firstElement() Returns the first element of the sequence.
indexOf(Object) Searches for the specified object, starting from the first position and returns an index to it.
indexOf(Object, int) Searches for the specified object, starting at the specified position and returns an index to it.
insertElementAt(Object, int) Inserts the specified object as an element at the specified index.
isEmpty() Returns true if the collection contains no values.
lastElement() Returns the last element of the sequence.
lastIndexOf(Object) Searches backwards for the specified object, starting from the last position and returns an index to it.
lastIndexOf(Object, int) Searches backwards for the specified object, starting from the specified position and returns an index to it.
removeAllElements() Removes all elements of the vector.
removeElement(Object) Removes the element from the vector.
removeElementAt(int) Deletes the element at the specified index.
setElementAt(Object, int) Sets the element at the specified index to be the specified object.
setSize(int) Sets the size of the vector.
size() Returns the number of elements in the vector.
toString() Converts the vector to a string.
trimToSize() Trims the vector's capacity down to size

Vectorii pot fi omogeni sau neomogeni. Exemplu:
Vector vectorNeomogen = new Vector();
vectorNeomogen.addElement(new Float(“3.141”));
vectorNeomogen.addElement(new Integer(20));
vectorNeomogen.addElement(new BitSet());
STIVA
STACK (java.util.Stack)
Extinde clasa Vector si implementeaza o stiva LIFO.
Constructor
Stack ()
Metode
empty () Returns true if the stack is empty.
peek() Peeks at the top of the stack.
pop() Pops an item off the stack.
push(Object) Pushes an item onto the stack.
search(Object) Sees if an object is on the stack.

Alte clase :
Date
Random
StringTokenizer
BitSet
Dictionary
HashTable extends Dictionary
Properties extends HashTable

Exemple de utilizare :
Date
• pentru afisarea zilei curente
Date d = new Date();
System.out.println("today = " + d);
• ziua corespunzatoare unei date
Date d = new Date(63, 0, 16); // January 16, 1963
System.out.println("Day of the week: " + d.getDay());

String Tokenizer
• descompunerea in unitati lexicale
String s = "this is a test";
StringTokenizer st = new StringTokenizer(s);
while (st.hasMoreTokens()) {
System.out.println(st.nextToken());
}
Va afisa :
this
is
a
test
Separatorii impliciti sunt atanar, dar pot fi definiti alti separatori in constructor :

String sir = “1+2*3/4”;
StringTokenizer analizor = new StringTokenizer(“sir”, “+-*/”);

Random
new Random()  construieste un generator de numere aleatoare
nextInt(),nextLong() returneaza o valoare aleatoare uniform distribuita de tipul specificat.
nextFloat(),nextDouble() returneaza o valoare aleatoare uniform distribuita intre 0 si 1,de tipul specificat.

HashTable
Permite implementarea tabelelor de dispersie. O tabela de dispersie este o tabela in care regasirea informatiei se face pe bza unei chei (etichete).
O functie utila care poate fi folosita impreuna cu tabelel de dispersie este hashCode(), care atribuie fiecarui obiect instantiat special un cod unic.

Properties
Este folosita pentru definirea multimilor de proprietati. Un astfel de exemplu este multimea proprietatilor sistem
...
java.version = 1.1.6;
os.name = Windows 95
...
Se observa ca, in cazul multimilor de proprietati, atat cheia cat si elementul memorat sunt siruri de caractere.
Ex: cheie=os.name, element=Windows 95
Functii : list, save, getProperty, etc.