instanceof

1
????? ???? 10

• ??????
• ????? ???????
• ????? ???? ??????
• ????? ???? ?????
• ?????
• ????? ???????
• ?????
• ??????? instanceof

2
??????

• ???? ????? ????? ?????.
• ?????? ??????, ????? ??? ????? ?????? ?? ?????
  ????? ????. ???? ???? ?? ?????????????? ???????
  ???? ??????? ?????? ????.
• ?????? ??????? ????? ???? ??????? (?????????)
  ????? ?????? ????? ?? ????? ????? ??? ????.
• ?? ???? ???? ???? ????? ???????? ?????? ?? ??
  ???? ????? ?????.

3
??????

• ????? (interface) ???? ??? ?-Java ?????? ??????
  ?????? ??? ????? ??????.
• ?????? ?????? ?????? ???? ???? ???? ???? ?? ????
  ?????? ?? ?????? ?????? ???? ??? ????? ?????
  ????? ??? ????? ?????? ?????? ?????? ????? ??
  ???? ??????? ??????.

4
??????

• ?????? ???? ????? ???? ????? ????? ??? ?? ??
  ??-????? ????? ?"? ???? ???.
• ???? ??? ??????? ??????? (????????) ?? ????? ??
  ?? ??-?????, ???? ??????????? ??? ??-???????
  ????? ??? ????.
• ?? ?? ????? ????? ???? ??? ????? ?? ??-???????
  ????? ??? ????? ?????? ???? ??????? ???? ????.

5
?????? ????? ???????

• ????? ?? ????
• public interface ltnamegt
• ltconstants listgt
• ltmethods listgt
• ?????? ?????? ????? (????????) ??? ?????.
• ?? ?????? ????? ?? ???????? (public) - ?? ?? ??
  ?????? ?? ??????
• ????? ???? ?????? ????? ??? ???? ?????????.
• ?? ????? ????? ?? ???????? ?????? ????? ??????
  ?????? (public static final) - ?? ?? ?? ??????
  ?? ??????.

6
?????? ????? ???????

• ??????
• public interface Predator
• boolean chasePrey(Prey p)
• void eatPrey(Prey p)
• ?????? ?????? ????? (????????) ??? ?????.
• ?? ?????? ????? ?? ???????? (public) - ?? ?? ??
  ?????? ?? ??????
• ????? ???? ?????? ????? ??? ???? ?????????.
• ?? ????? ????? ?? ???????? ?????? ????? ??????
  ?????? (public static final) - ?? ?? ?? ??????
  ?? ??????.

7
?????? ????? ???????

• ????, ????? ??????, ????? ?????.????, ??????
  ???????? ?????? ????? ??????? ????? ????
  ????.????, ???? ?????? ?? ????? x ????? ????
  Predator
• Predator x
• ?? ???? ????? ??????? ?????. ????
• x new Predator()

// will not compile !!!
8
?????? ????? ???????

• ????? ?????? ???? ????? ???? ?? ?? ???????. ????
  ?????? ?? ????? ????? ????? ???? ??
• class Tiger implements Predator
• ????? ??? ????? ???? ?? ?? ????? ????? (?????
  ?????????). ?????? ?? ???? ??? ?? ??????
  ??????????, ????? ???? ????? ?????. ?????
  ????????? ?? ????? ???? ?? ?? ?????? ?? ????.
• ????? ????? ???? ???? ????? ???! ???? ?????
  ?????

9

• public interface Predator
• boolean chasePrey(Prey p)
• void eatPrey(Prey p)
• public class Tiger implements Predator
• public boolean chasePrey(Prey p)
• // code to chase prey p (specifically for a
  tiger)
• return runAfterPrey(p)
• public void eatPrey (Prey p)
• // code to eat prey p (for a tiger)
• chew(p)
• swallow(p)
• ...

10

• public interface Predator
• boolean chasePrey(Prey p)
• void eatPrey(Prey p)
• public class Shark implements Predator
• public boolean chasePrey(Prey p)
• // code to chase prey p (specifically for a
  shark)
• return swimAfterPrey(p)
• public void eatPrey (Prey p)
• // code to eat prey p //(specifically for a
  shark)
• bite(p)
• swallow(p)

11

• ???? ??? ???? ??? ??? ??? ????.
• ????? ????? ?????? ???? ?? ?????, ????? ??????
  ????, ?????? ???? ?? ?????? ??????? ??????
  ??????? ?? ?? ??? ???????? ?????.
• Predator preds new Predator3
• preds0 new Tiger()
• preds1 new Shark()
• preds2 new Shark()
• Prey froggy new Frog()
• for (int i0 iltpreds.length froggy.isAlive()
  ii1)
• frog.runAway()
• if (predsi.chasePrey(froggy))
• predsi.eatPrey(froggy)
• ???? ????? ?????? ?? ??? ?????, ????? ?"?
  ??????? ?????. ??? ???? ?? ??? ????? ????, ?????
  ???? ????? ???? ?? ??? interface Prey.

??? ???? ??? ?????? froggy.jump() ?
12

• ?? ???? ???? ????? ???? ???? ???? ???? ????
  ?????? ????????
• public static void simulateChase(Predator predat,
  Prey prey)
• prey.runAway()
• if (predat.chasePrey(prey))
• predat.eatPrey(prey)
• ????? ?????? ?????? ?? ??????? ????? ???? ??????
  ?????, ????? ?????? ?????? ???? ???? ?? ???
  ?????? ?????? ????????.
• Shark sharky new Shark()
• Frog kermit new Frog()
• simulateChase(sharky, kermit)
• ???? ??, ???? ??? ?? ?????
• Predator sharky new Shark()
• Prey kermit new Frog()
• simulateChase(sharky, kermit)

13

• ????, ?????, ?????? ?????? (?????) ???? (????)
  ??????? ??????, ??? ??? ????? ???? ?????. ??????
• public class Shark implements Predator
• String name
• int numOfTeeth
• public Shark(String name)
• this.name name
• numOfTeeth 3000 (int)(Math.random()1000)
  
• private void swallow(Prey p)
• p.die()
• public int getNumOfTeeth() return numOfTeeth
  
• public void swimForFun() ...
• public void eatPrey (Prey p)
• bite(p)
• swallow(p)

14

• "???" ??? ?? ?? ???? ???? ?? ????, ?????? ????
  ???? ?????? ???????. ???? ?? ?? ?? ????
• public interface Prey
• public boolean isAlive()
• public void die()
• public void runAway()
• ????? ?????? ?????? ???? "???"
• public class Frog implements Prey
• private boolean living
• public Frog()
• living true
• public boolean isAlive() return living
• public void die() living false
• public void runAway() ...

15

• ????? ???? ??????
• ???? ???? ???? ????? ???.
• ?? ?????? ??????? ???? ?? ????????? ?? ??
  ???????.
• ?? ????? ?????? ??? ?????? ???? ???? ???? ?? ???
  ???? foo ??
• ?? ???? ? foo ?? ????? ???? ?? ?????? ???????
  ????? ???? ?? ?????.
• ?? ???? ? foo ?? ???? ????? ????? ????? ????? ??
  ?????? ?????? ?? foo ???.
• ?? ???? ? foo ?? ???? ????? ?? ????? ????? ????
  - ???? ?????????. (?? ???? ???? ?? ??? ???????
  ???).
• ?? ??? ????? ?? ????? ????. ??? ???? ????? ????
  ?? ????? (?????? ???? ???? ??? ????? ??)
• public class Frog implements Prey, Predator
• public boolean chasePrey(Prey p)
• ...
• public void eatPrey (Prey p)
• ...
• ...

16

• ??? ?????? ????? ???? ?? ??? ????????
• Shark sharky new Shark()
• Frog kermit new Frog()
• Fly bzzit new Fly()
• simulateChase(sharky, kermit)
• if(kermit.isAlive())
• simulateChase(kermit, bzzit)
• sharky.swimForFun()

??? ???? ??? ?????? ?? sharky ?-Predator? ???
???? ??? ?????? ?? kermit ?-Prey? ??? ???? ???
?????? ?? bzzit ?-Prey?
?? ?? ??
???? ?? ????? (?? ????) ?? ???? ????? ??????
17

• ???? ?????
• ????? ???? ?"??? ????" ?? ?????????.
• ???? ???? ?? ??? ?????? ???? ????? ????? ???.
  ???? ?????? ??? ?????. ???? ????? ????? ??? ????,
  ???? ?? ???? ??? ????. ??? ?? ????? ?? ??????
  equals ?????? ?? ???? ????? ???? ???? ???.
• lt first element, second element gt
• ?? ???? ????? ???? ??? ????. ???? ????? ???
  ??????, first ?-second, ?? ????? ???? ????? 2.
• ???? ?? ?? ????? orderedEquals ????? ??? ????
  ???, ?????? ?????? ???? ??? ????? (??? ??????,
  ???? ?? ????). ?? ???? ?????? ????? ??? ????
  ?????? ?????? (?????) OrderedPair ???? ???.
• public interface OrderedPair
• public Object getFirst()
• public Object getSecond()
• public boolean orderedEquals(OrderedPair
  another)
• public boolean unorderedEquals(OrderedPair
  another)

18

• ???? ?????

public class PairAsFields implements OrderedPair
private Object first, second public
PairAsFields(Object x, Object y) first
x second y public Object getFirst()
return first public Object getSecond()
return second public boolean
orderedEquals(OrderedPair another) return
first.equals(another.getFirst())
second.equals(another.getSecond()) public
boolean unorderedEquals(OrderedPair another)
return (getFirst().equals(another.getFirst())
getSecond().equals(another.getSecond()))
(getFirst().equals(another.getSecond())
getSecond().equals(another.getFirst()))

19

• ???? ?????

public class PairAsArray implements OrderedPair
private Object pair public
PairAsArray(Object a, Object b) pair new
Object2 pair0 a pair1 b
public Object getFirst() return pair0
public Object getSecond() return pair1
public boolean orderedEquals(OrderedPair another)
return pair0.equals(another.getFirst())
pair1.equals(another.getSecond()) public
boolean unorderedEquals(OrderedPair another)
return (getFirst().equals(another.getFirst())
getSecond().equals(another.getSecond()))
(getFirst().equals(another.getSecond())
getSecond().equals(another.getFirst()))

20
?????
21
?????

• ?????? ????? ?? ???? ?????? ??? ??????????
  ???????? ????????.
• ????? ????? ????? ?? ???? ????? ??. ?????
• ????? ??????? ??????? ????? ????????? ???? ???
  ??????, ????? ??????.
• ??? ?????? (subclasses), ??????, ??????? ?????
  ????, ????? ???? ???????? ?? ????? ??? ?? ???
  ?? ??????? (?? ???????? ??????? ?????).
• ????? ???????? ??? ????? ?? ?? (superclass) ??
  ?????? ????? ???? ?????? ????.

22
?????

• ?? ?? ????? ????? ?????? ??? ??? ??????? ????.
• ??? ?????? ???????? ??????
• ??????? ??? (????) ??????? ??? ?????? ????????,
  ???
• ????????? (?????) ??????? ??? ?????, ?????,
  ????? ???????.
• ??????? ??? ??????? ???? ?????? ???????? ?????
  ???.
• ??? ?????? ?????? ?????? ???? ?????? ?????, ????
• ????? ???? ?????? ????? ????
• ???????? ?? ????? ??? ?? ????? ???, ???'.

23
?????

• ??? ?????? ????????? ?????? ??? ????? ?? ??????
  ???????? ???? (????? ????).
• ??? ??????? ??? ???????, ?? ?????? ???? ???????.
• ????? ???? ??????? ????? ?????? ???? ???? ???????
  ??????.
• ??? ?????? ?????? ????? ?? ?????? ???? ?? ??????.
  
• ???? ????? ??????? ??? ????? ?????? ???????,
  ???? ???? ???? ????? ????? ???? ??? ?? ???
  ??????? ???????, ???'
• ????? ???? ?????? ???? ???. ???? ?????? ??
  ?????? ???? ?? ??????? ??? ????.
• ????? ???? ???????

24
????? - ?????

• ????? ????? ??????
• 1. ????? ????? ?????? (?????) ?? ????? ???.(????
  ?????? ??????? ?? ?? ???? ?????????? ??????)

25
????? - ?????

• 2. ????? B ????? ?? A ?? ???? ????
• "B ??? ??? ?? A".
• ?-Java ????? class B extends A

???????
A
????? ????
B
26
????? - ?????

• 3. ??????? ????? (?????? B) ???? ????? ??
  ???????? ?????? (?????? A).
• 4. A ??? ? parent class ?? ? super class ?? BB
  ??? ? subclass ?? child class ?? A

????? ???? - public void race()
???????
A

• ???????
• - color Red
• speed 50 km/h- public void ride()

????? ????
B
27
????? - ?????

• 5. B ????? ?? ?? ?????? ???????? ????? private
  ?-A???? ??????.?? ???? ???? ???? B ?????? ??
  ???? ?????? ?-A ?? ?? ??? ?????? (???? ????? ????
  ????? ????? ?????, ?????? ?? protected)

class A private int aNum class B
extends A private int bNum public
B() aNum0 bNum 0
// ? compilation error
28
????? - ?????

• 6. ????? ???? ?????? ??????! ??? ?? ?????? ?????
  ?????
• 7. ???????? ??????? ??? ???? B, ????? ?? ????? A
  ???? ??????.
• ???? ????? ?? ????? ?????, ???? ???? ?????
  ??????? ????? ???-??????? ?? A.
• ????? ?????? ????? ?"? super(). super ???? ???
  ????? ???? Java,??? ?????? ?? ????? ???.

class A private int aNum public
A(int n) aNum n
class B extends A private int bNum
public B() super(0) bNum 0

//calls the constructor of A
29
????? - ?????

• ?? ???? ????? ???

class B extends A private int bNum
public B() bNum 0
class A private int aNum public
A(int n) aNum n
?? ????? ?????????! no empty constructor for
A Cannot find symbol constructor A()
30
????? - ?????

• 8. ?????? ? super ????? ????? ????? ??????? ?????
  ?? B
• ?? ???? ????? ???

class B extends A private int bNum
public B() bNum 0 super(0)

class A private int aNum public
A(int n) aNum n
????????? ???? ??? ?- 2 ?????? ?????????!

• Cannot find symbol constructor A()
• Call to super must be first statement in
  constructor

31
????? - ?????

• ????? Overriding
• ????? ????? ???? ??-????? ?????? ???? ???? ?????
  ??? ????? ??????? ?????? ???
• ???? ????? ??????, ?????? ?? ???????? (instance)
  ?? ????? ???? ??? ?????? ??????? ???????
  ????? ???? ??????? ?????.
• ?????? ????? ?????? ???????? ??? ??????
  (reference) ?? ????? ?????? ?????? ?????
  ???????
• ????? ????? ?? ?????? ????? private.
• super - ?? ????? ????? ????? ????? ???????? ??
  ??? ???? ?????? ????? super.

32
????? - ?????

• 11.(?????) vs. Overloading Overriding (?????)
• ????? ??? ???? ???? ???? ?????? ???????? ????
  ???? ?? ?? ?? ??????? ????? ????? ??????.
• ????? ??? ????? ?? ??? ????? ????? ????? ???, ???
  ?????? ??? ???? ?????? ???.
• ????? ?????? ????? ???? ???? data ????
• ????? ?????? ???? ????? ???? ???? ????? ???????
  ????.

33
????? - ?????

• 12. ???? ????? ???????? ????? ?????, ?? ?????? ??
  ?? ????? ??? ????? ????? ????? ?? ?? ????? ????.

34
????? - ?????

• 13. ?? ????? ?????? ????? ????? ?? ????? ??
  ?????? Object, ???? ????? ????????? ??????.

Object
35
????? - ?????

• ?????? Object ??????? ???????? ????????????
  (?????? ?????, ?? ????? default) ?? ??????
  toString, equals ????
• public String toString()
• public boolean equals(Object obj)
• ???? ????? ??? ?????? ???????? ?"? ????? ????
  ???????

?? ?? ???? ?? ????? ???? ????? A ?? ?????
???? ?? public boolean equals(A other)
!! ?? ?????? ????? ?? ????? equals ?? ????? ???
Object, ???? ??????? ????.
36
????? 1
class A private int aNum public A(int
n) aNum n public void
inc(int n) aNum aNum n
class B extends A private int bNum
public B() super(0) bNum 0
public void inc(int amount) //
overrides inc(int) of A
super.inc(amount) //increment aNum
bNum amount //increment bNum

B - bNum 16 - void inc(int)

• A
• - aNum 10
• void inc(int)

37
????? 2
class A private int aNum public A(int
n) aNum n public void
inc(int n) aNum aNum n
class B extends A private int bNum
public B() super(0) bNum 0
public int inc(int amount) //
compilation error! Cannot override!
super.inc(amount) bNum
amount return bNum
- ?? ???? ????? ???? ?? ????? ??? ?????? ?????
????
B - bNum 16 - int inc(int)

• A
• - aNum 10
• void inc(int)

???? ?? ???? ???? ????? ?????? ??? ???????
????? ?????? ?????? ?? ????? ??????, ?? ?? ????
??? ????
38
????? - ?????

• 15. ??????? instanceof??? ??????? ?????? true
  ?? ??? ?? ???????? ?????? ??? ???? (instance) ??
  ?????? ?????? ?? ????????. ???????

class Cat interface ShowAnimal class Siamese
extends Cat implements ShowAnimal
39
????? - ?????
class Cat interface ShowAnimal class Siamese
extends Cat implements ShowAnimal
Cat myaoo new Cat() Cat mitzi new
Siamese()
//true //true //Compilation Error
System.out.println(myaoo instanceof Cat)
System.out.println(mitzi instanceof Cat)
System.out.println(myaoo instanceof "Cat")
System.out.println(mitzi instanceof
Siamese) System.out.println(myaoo instanceof
Siamese)
//true //false
//true //true
System.out.println(mitzi instanceof
ShowAnimal) System.out.println(mitzi instanceof
Object)
40
????? - ?????
class Cat interface ShowAnimal class Siamese
extends Cat implements ShowAnimal
Cat myaoo new Cat() Cat mitzi new
Siamese()
System.out.println(mitzi instanceof myaoo)
//Compilation Error
//Compilation Error // operator ! cannot be
applied to Cat
System.out.println(!mitzi instanceof Cat)
//false
System.out.println(!(mitzi instanceof Cat))
Cat pitzi null System.out.println(pitzi
instanceof Cat) System.out.println(null
instanceof String)
//false //false