Collections

Question 1

Syntaxe vytvoreni String pole
prazdne
hodnotami (2)

Answer 1

String[] array = new String[2];
String[] array = new String[] {“a”, “b”};
String[] array = {“a”, “b”};

Question 2

Prazdne pole ma po vytvoreni v komurkach co?

Answer 2

defaultni hodnoty

Question 3

Syntaxe vytvoreni dvourozmerne matice Byte
prazdne
hodnotami

Answer 3

Byte[][] matrix = new Byte[2][3]; // radek, sloupec
Byte[][] matrix = {{1,2,3},{2,3}} // 2 radky, 3 sloupce, posledni hodnota je 0

Question 4

Metody kopirovani z pole do pole (3)

Answer 4

System.arraycopy(source, sposition, destination, dposition, length)
var x = Arrays.copyOf(source, position)
var x = Arrays.copyOfRange(source, position, length)

Question 5

Jak seradit prvky v poli
Jak seradit prvky v kolekci

Answer 5

Arrays.sort(array, comparator)
Collections.sort(collection, comparator)

Question 6

Jak se kompilator chova k generics

Answer 6

Smaze je - nahradi za Object. Ale kde se pouzije hodnota, pretypuje se na spravny typ.

Question 7

Wildcards:
neznamy typ
nadtyp (nebo stejny) - lowerbound wc.
podtyp (nebo stejny) - upperbound wc.
- syntax + ktery z nich definuje read only kolekci?

Answer 7

List<?>
List<? super X>
List<? extends X>

List<?>

Question 8

List<Product> products = new ArrayList<Food>(); projde?</Food></Product>

Answer 8

ne, collections jsou invariantni - typ musi sedet

Question 9

Product[] products = new Food[]; projde?

Answer 9

ano, arrays jsou covariantni - typ muze byt urcitejsi

Question 10

Ifc kolekce pro oboustrannou frontu + impl (3)
Jaka je impl. velikost?

Answer 10

Deque<T> d = new ArrayDeque<>();
new ArrayDeque<>(list);
new ArrayDeque<>(20);
16</T>

Question 11

Oboustranna fronta - metody:
insert dopredu/dozadu
get odpredu/odzadu
get&remove odpredu/odzadu

Answer 11

offerFirst, offerLast
peekFirst, peekLast
pollFirst, pollLast

Question 12

Pristup oboustranne fronty k null

Answer 12

Null hodnoty nelze vkladat
Gettery vraci null, pokud je kolekce prazdna

Question 13

Kolekce key,value ifc+impl (3)
Jaka je implicitni velikost?

Answer 13

Map<T> m = new HashMap<>();
new HashMap<>(100);
new HashMap<>(otherMap);</T>

Question 14

Iterator na kolekci:
podminky, vytvoreni
jak zjistim, vratim, odstranim prvek?

Answer 14

implements Iterable
coll.iterator()
hasNext(), next(), remove()

Question 15

Jaka je podminka kolekce, aby mohla lezt do foreach

Answer 15

implements Iterable

Question 16

Seznam - ifc+impl (3)
Jaka je impl. velikost

Answer 16

List<T> l = new ArrayList<>();
new ArrayList<>(100);
new ArrayList<>(set);</T>

Question 17

Metoda pro vytvoreni immutable seznamu, pokud mas prvky

Answer 17

List.of(a, b, c);

Question 18

Metoda pro vytvoreni mutable seznamu, pokud mas prvky (mohou byt v poli)

Answer 18

Arrays.asList(a, b)
Arrays.asList(a[])

Question 19

Seznam metody:
pridej a posun (2p), pridej a prepis prvek
odstran (2p)
obsahuje prvek
jakou ma prvek pozici

Answer 19

add(T), add(index, T), set(index, T)
remove(index), remove(T) - prvni nalezeny
contains(T)
indexOf(T) - pokud neni, vraci -1

Question 20

HashSet
co je dobre pro vykon
co naopak ne
je thread safe?

Answer 20

+ rovnomerne rozdeleni hashu
- nadstrelena kapacita
nema, to ma SynchronizedSet

Question 21

Load faktor na kolekci
Defaultni pro HashSet

Answer 21

O kolik se kapacita zvetsi pri pridani prvku nad
0.75

Question 22

Set - ifc+impl (4)
Implicitni kapacita

Answer 22

Set<T> s = new HashSet<>();
new HashSet<>(100);
new HashSet<>(100, 0.75);
new HashSet<>(coll);
16</T>

Question 23

Metoda vytvoreni immutable mnoziny z prvku

Answer 23

Set.of(a, b, c)

Question 24

Set - metody
pridej, odeber, zjisti

Answer 24

add, remove, contains

Question 25

Metody menici poradi prvku v kolekci (3)

Answer 25

Collections.sort(c)
Collections.revers(c)
Collections.shuffle(c)

Question 26

Metoda vyhledani prvku v kolekci

Answer 26

Collections.binarySearch(c, element)

Question 27

Metoda naplneni pole stejnymi hodnotami

Answer 27

Collections.fill(c, value)

Question 28

Metoda pro odstraneni prvku nesplnujicich podminku z kolekce

Answer 28

collection.removeIf(predicate)

Question 29

Metoda ulozeni kolekce do pole

Answer 29

collection.toArray(array)

Question 30

Implementace mnoziny (4)

Answer 30

HashSet, TreeSet, SortedSet, SynchronizedSet

Question 31

Kolekce maji/nemaji thread safe operace?

Answer 31

Maji

Question 32

Metody pro praci s polem:
vyplneni hodnotou
nalezeni prvku
jsou pole stejna
serad(2)

Answer 32

Arrays.fill(array, start, end, value)
Arrays.binarySearch(array, value)
Arrays.equals(a, b)
Arrays.sort(array), Arrays.sort(array, comparator)

Question 33

Priklad implementace komparatoru

Answer 33

public class MyComp<T> implements Comparator {
public int compare(T t1, T t2) {
return t1.compareTo(t2);
}
}</T>

Question 34

Vyhodnocovani v array, co se vyhodnoti driv
a[(a=b)[2]

Answer 34

Nejdriv vnejsi a, potom vnitrek

Question 35

Jak se da provest akce nad mapou
- pomoci lambdy

Answer 35

map.forEach((k, v) -> action(k,v));

Question 36

Jak se da provest akce nad listem
- pomoci existujici metody

Answer 36

list.forEach(SomeClass::method);

Question 37

Co se stane, pokud vytvorim: Set.of(1,2,2,3)

Answer 37

Runtime error
Set je immutable a nemuze obsahovat stejne prvky

Question 38

Generics pro potomky tridy

Answer 38

<T>
</T>

Question 39

Je Comparator functional interface?

Answer 39

Jo

Question 40

retezeni komparatoru sekvencne - syntax

Answer 40

comparator1.thenComparing(comparator2)

Question 41

uprava komparatoru:
zachazeni s nully (2)
obracene poradi

Answer 41

C.nullsFirst(c);
C.nullsLast(c);
c.reversed();

Question 42

Klonovani
- podminka (+trest)
- syntax
- jaka trida ma implementaci clone
- co dela

Answer 42

Trida implementuje Cloneable (vyjimka pri klonovani)
Product p2 = (Product) p1.clone();
Object
Kopii objektu na heapu

Question 43

Definuj predicate nad Stringem ze neni empty

Answer 43

Predicate<String> nonEmpty = (x) -> !x.isEmtpy();</String>

Question 44

jak funguje list.add(index, element)

Answer 44

Prida prvek na index a posune zbytek doprava.
Element
- zkopiruje do sebe, pokud je to primitiv
- zkopiruje! do sebe referenci, pokud je to objekt
(pozor u GC, tady se drzi druha reference)

Question 45

Metoda, ktera pro dany klic K nahradi hodnotu, pokud je rovna V, za V1

Answer 45

map.replace(K, V, V1)

Question 46

Vytvor komparator podle length (comparing

Answer 46

Comparator.comparing((x) -> x.length())

Question 47

Vytvor komparator podle length (comparing

Answer 47

Comparator.comparing((x) -> x.length())

Question 48

Jak vytvorim map pro paralelni zpracovani, load factor 0.8, kapacita 5 a concurrency level 15 (max pocet vlaken)

Answer 48

new ConcurrentMap(5, 0.8f, 15)

Question 49

Jak zapisu seznam do arraye

Answer 49

var myArray = list.toArray(someArray);
pokud se vejde, vratim puvodni array, jinak novy