Syntax & common stuff

Question 1

stary switch - syntax + chovani (break, default (3))

Answer 1

switch (x) {
case 1: case 2: logic(); logic();
case 3: logic(); break();
default: logic();
}
- po matchnute vetvi se aplikuji vsechny! pokud neni break
- default se pouzije, pokud se nematchne; neni povinna; nemusi byt posledni

Question 2

switch novy (bez navratu) - syntax + chovani (break)

Answer 2

switch(x) {
case 1,2 -> logic();
case 3 -> { logic(); logic(); }
default -> logic();
}
break se nepise, je automaticky za kazdou vetvi

Question 3

switch expression - syntax

Answer 3

int a = switch(x) {
case 1, 2: 10;
case 3: { logic(); yield logic(); }
default: yield 20;
}

Question 4

while - syntax (2)

Answer 4

while (test) { action(); }
do { action(); } while(test)

Question 5

for syntax:
vice promennych
vzdy true
foreach
foreach z matice

Answer 5

for (int i = 0, j=1; i<5 && j<10; i++, j++) {}
for (;;) {}
for (String str: list) { sout(str); }
for (char[] row: matrix) {}

Question 6

label, break, continue

Answer 6

MyLabel:
break; - ukonci loop
break MyLabel; - vyskoci z celeho obsahu label
continue; - pokracuje dalsim cyklem
continue MyLabel; - skoci na label

Question 7

Jak se vola interpreter
Co neni dovoleno (6)

Answer 7

jshell z cmd
nepovoleno: package, static, final, break, continue, return

Question 8

jshell - otevri file.txt, skonci

Answer 8

/open file.txt
/exit

Question 9

Co musi obsahovat casy switche

Answer 9

Musi pokryvat vsechny moznosti, nebo mit default

Question 10

Jaka podminka plati pro razeni typu v casech
Priklad CharSequence, String

Answer 10

Nesmi byt superclass pred jeji subclass
case CharSequence c
case String s
je spatne, protoze String je potomek CharSequence

Question 11

String.isEmpty()

Answer 11

prazdny string nebo whitespaces only

Question 12

StringBuilder vs StringBuffer

Answer 12

StringBuffer je thread save, StringBuilder ne
StringBuilder je rychlejsi, pokud potrebuju 1 vlakno

Question 13

Co se stane?
switch (x) {
case Character c : action();
case String s : action();
default : action();
}

Answer 13

Compilation error
Protoze telo druheho casu ma s i c
Chyba napr. i pro Character+Long
Lze vyresit breakama

Question 14

void method() {
int x;
sout(x);
}

co se stane?

Answer 14

compilation error
lokalni promenna se musi pred pouzitim inicializovat

Question 15

Smi cases obsahovat enum?

Answer 15

Jejich values (int) ano, ale samotny enum ne