Inheritance & Interfaces

Question 1

Předpis abstraktní třídy s metodou

Answer 1

public abstract class MyClass {
public abstract void m();
}

Question 2

Co je abstraktní třída/metoda?

Answer 2

Třída obsahující aspoň jednu abstraktní metodu
Metoda bez implementace
Dědící třída ji musí implementovat

Question 3

Kolik smí třída rozšířit tříd a implementovat interface?

Answer 3

Rozšířit 1, implementovat kolik chce

Question 4

Předpis interface s metodou

Answer 4

public interface Ifc {
public void method();
}

Question 5

Druhy inner class

Answer 5

Static - pro tridu
Member - pro instanci
Local - v metode
Anonymous - inline implementace / rozsireni ifc/class

Question 6

Modifikatory viditelnosti tridy

Answer 6

private - jen ja a moje inner classy
default (=nepise se) - vsichni v mem pkg
protected - vsichni v mem pkg a moji potomci
public - vsichni (v modulu)

Question 7

Jak se vytvori instance staticke tridy Nested bydlici ve tride Outer

Answer 7

Outer.Nested nested = new Outer.Nested();

Question 8

Trida Outer obsahujici statickou tridu Nested.
Kdo vidi private veci tridy Nested?
Jak lze takovou tridu s privatnim konstr. instanciovat?

Answer 8

Nested, Outer
Outer.Nested x = Outer.createNestedInstance();

Question 9

Trida Outer obsahujici statickou tridu Nested.
Kdo vidi private veci tridy Outer?

Answer 9

Outer, Nested
Outer, Nested take, ale jen staticke

Question 10

vytvareni member inner class

Answer 10

nejprve se musi vytvorit instance outer class

Question 11

local inner class - hranice existence, jake promenne muze pouzit

Answer 11

existuje jen uvnitr metody
muze pouzit promenne a parametry metody, jen pokud jsou final / efektivne final

Question 12

Co je efektivne finalni promenna?

Answer 12

Hodnota se priradi jednou a nikdy se nezmeni

Question 13

Co je functional interface?
Syntax

Answer 13

Ma prave jednu metodu k implementaci
Muze obsahovat i dalsi cleny
nepovinna anotace nad ifc: @FunctionalInterface

Question 14

Anonymni trida - syntax

Answer 14

var anonymousClass = new ParentClass/Ifc() {
@Override
//method defitintion
}

Question 15

Anonymni trida - inline syntax pro func. ifc: scitani

Answer 15

var anonymousClass = (a, b) -> a+b;

Question 16

Co je default implementation metoda v ifc?
Co je jeji opak?
Co muze udelat potomek? (3)

Answer 16

Je to metoda, ktera ma implementaci.
Abstraktni metoda
Nic - zdedi ji
Prepsat - vlastni implementace (povinne, pokud je ve vice mych ifc)
Deklarovat - jako abstraktni, jeho potomek ji musi prepsat

Question 17

defaultni metoda - syntax

Answer 17

(public) (default) void method() { /* impl */ }

Question 18

Co je lambda?
Syntax
- nechci menit hodnotu parametru v tele a vracim hodnotu
- vracim hodotu jedinym radkem

Answer 18

Inline implmentace funkcionalniho interface
(x, final String y, final var z) -> { action(x, y, z); return 0; }
(x, y, z) -> 0;

Question 19

Method reference - syntax (3)

Answer 19

MyClass::method
myInstance::method
MyClass::new (=konstruktor)

Question 20

public class MyClass {
public int method(String x) { return 0; }
}
preved na method reference
preved na lambdu

Answer 20

MyClass::method
(x) -> 0

Question 21

Nested member class - syntax

Answer 21

public class Outer {
private/public class Inner {
…
}
}

Question 22

Nested static class - syntax

Answer 22

public class Outer {
private/public static class Inner {
….
}
}

Question 23

Local inner class - syntax

Answer 23

public void method(final var p, var q) {
class Inner {
…. // p je videt, q neni
}
Inner inner = new Inner();
}

Question 24

Interface - jaka klicova slova jsou implicitni pro metodu v ifc, tedy byly vynechany?
void method();

Answer 24

public abstract

Question 25

Staticka metoda v ifc

Answer 25

Zustava parentovi, vola se:
var result = Ifc.method();

Question 26

Pri implementaci metody co je dovoleno?
prepsat public na private (zuzit access)
prepsat private na public (rozsirit access)

Answer 26

prepsat private na public (rozsirit access)

Question 27

Syntax interface - IfcChild, ktere dedi z IfcParent

Answer 27

public interface IfcChild extends IfcParent { }

Question 28

Stejna metoda v mem rodici a ifc.
Ktera plati?

Answer 28

V rodici (superclass)

Question 29

Stejna default metoda v mem ifc i v jeho nadrazenem ifc
Ktera plati?

Answer 29

blizsi ifc

Question 30

Stejna default metoda ve dvou mych ifc
Ktera plati?

Answer 30

Zadna, musim ji prepsat.

Question 31

public void method() {…}

@Override
public void method() throws Exception { … }

Lze mit pri prepsani jinou vyjimku nez rodic?

Answer 31

Jo

Question 32

Can interface have instance field?

Answer 32

No

Question 33

Can interface have final method?

Answer 33

No

Question 34

Prepsani metody. V cem se muze lisit navratovy typ?

Answer 34

Muze byt subclass navratove hodnoty z puvodni metody