inheritance

1
????? inheritance

• ????? ?????? ????? ?????? ????? ?????? ?????
  ???????? ?? ?????? ??????.
• ?????? ?????? ????? ???? ?? ????? ???? (parent
  class, base class)
• ?????? ?????? ????? ????? ?? ?? ??-????? (child
  class, subcluss)

2
?????

• ?????? ?????? ????? ?????? ??????. (??????
  ????? ?? ????? ?? ????).
• ?????? ???? ?????? ?????? ?????? ????? ?? ????
  ?????? ?? ????? ?? ???? ???? ??????.
• ????? ???? ???? (code reuse) ??? ?????????
  ??????? ?????? ??????.
• ??? (???????) ?????? ????? ????? ?????? ?????? ??
  ????? ?????.

3
???? ??????
this
????? ??
Field Y
Field X
Method X
super
????? ??
Field A
Field B
Method A
Method B
Method C
4
Triangle.java

• public class Triangle implements Shape
• protected double a,b,c
• protected String color
• public Triangle(double a, double b, double c,
  String color)
• this.a a
• this.color color
• System.out.println("New triangle crerated\n"
  
• "Sides a"a" b"b" c"c)
• public double area()
• double s perimeter()/2
• System.out.println("Calculating the area\n"
  
• "Heron formula A sqrt(s(s-a)(s-b)(s-c))")
  
• return Math.sqrt(s(s-a)(s-b)(s-c))
• public double perimeter() return abc

5
EquilateralTriangle.java

• public class EquilateralTriangle extends Triangle
  
• public EquilateralTriangle(double a, String
  color)
• super(a,a,a,color)
• System.out.println("New equilateral triangle
  crerated\n"
• "Side a"a)
• public double getAngle() return 60.0
• public double area()
• System.out.println("Calculating the area\n"
  
• "Equilateral formula A 0.5aasin(60deg)"
  )
• return 0.5bbMath.sin(Math.PI/3.0)

6
?????

• ?????? ?????? ?????? ?? ????? ????? ???? "???
  ??..."
• ????? ?????? protected ???? ?? ???? ?? ????? ????
  ?????? ??????? ?????? ?? ?? ??????? ????????.
• ???? ?? ????? private ?? ???? ?????? ??????
  ?????.
• ?????? ?????? ????? ????? (override) ????? ??
  ????? ?????.
• ?????? ?????? ????? ?????? ????? ?? ???? ???
  ?????.

7
????? ?-super

• ?????? ?????? ???? ????? ?? ?????? ?? ????? ?????
  ?? ?? ?? public.
• ???? ?????? ?? ????? ????? ????? ???? ??????, ??
  ??? ???? ????? ?????? ?? ???? ????? ??? ?????
  ?????.
• ????? super ????? ?????? ?????? ??? (??? this
  ?????? ?? ?????? ?? ????) ????? ?????? ?? ????
  ????? ?????? ?????.
• super ???? ?????? ????? ??????? ?? ?????. ?? ????
  ????? ????? ?????? ???? ?????? super().
• ???? ?????? ?super- ?? ?? ?????. ??????
  super.area()

8
multiple inheritance

• ????? ????? ???? ????? ???? ?? ?? ????? ??? ?????
  ?????.
• ???? ?????? ??? public ?? protected ?????? ??
  ?????? ??????.
• ?????? ????? ????? (??? c), ????? ????? ??
  ????? ???? ???? ?????? ???.
• ????????? ?????? ????? ??? ????? ???????.

9
????? overriding

• ?????? ?????? ????? ????? (override) ???? ??
  ????? ?????, ?? ?????? ???? ???? ???? ?????
  ??????.
• ???? ??????? ?? ?????? final ?? ????? ??????.
• ???? ????? ?? ????, ?? ?? ???? ????? ?????.
• ???? ??????? ??????? ?????? ?????? ?????? ?????
  ?"? super.

10
?????? instanceof

• ????? ???????? ??????? true ????? ?-instance ??
  ????? ??? ??? ?? ????? ????. ??????
• Triangle tri1 new Triangle(1.0 , 1.0 , 1.0 ,
  "Blue")
• Triangle tri2 new EquilateralTriangle(2.0
  , "Blue")
• EquilateralTriangle tri3 new
  EquilateralTriangle(3.0 , "Blue")
• System.out.println(tri1 instanceof
  Triangle) // true
• System.out.println(tri3 instanceof
  Triangle) // true
• System.out.println(tri3 instanceof Shape)
  // true
• System.out.println(tri1 instanceof
  EquilateralTriangle) // false
• System.out.println(tri2 instanceof
  EquilateralTriangle) // true

11
?????? ?????????? (abstract classes)

• ????? ???????, ?????? ?????????? ????? ?????? ???
  ???????, ?????? ???? ?????? ?? ????.
• ????? ????????? ??? ????? ??? ?? ???? ?????????
  ??? ?? ????.
• ????? ?????? ????? ????????? ????? ????? ?? ??
  ?????? ??????????? ?????? ?? ???. ?? ???? ????
  ???, ???? ????? ?????? ??????????.
• ??? instance ?????? ?????????, ???? ?????? ?????
  ??? ??? ????? ??????.

12
Polygon.java

• public abstract class Polygon
• protected double sides
• protected double angles
• public Polygon()
• public Polygon(double sides, double
  angles)
• this.sides sides
• this.angles angles
• public abstract double area()
• public double perimeter()
• double s 0.0
• for (int i0 iltsides.length i)
• s sidesi
• return s

13
EquilateralTriangle.java

• public class EquilateralTriangle extends Polygon
  
• public EquilateralTriangle(double a)
• sides new double3
• angles new double3
• sides0 sides1 sides2 a
• angles0 angles1 angles2
  Math.PI/3.0
• System.out.println("New equilateral triangle
  crerated\n"
• "Side a"getSide(1))
• public double area()
• System.out.println("Calculating the area
  (I'm an equilateral triangle)\n"
• "Equilateral area formula A
  0.5aasin(60deg)")
• return 0.5getAngle(0)getAngle(0)Math.sin(g
  etAngle(0))

14
????? ?? ??????

• ?? ?????? ?????? ???? ?? ???? ??????.
• ???? ????? ???? ??? ???? ?? ?? ?? ??????
  ??????????? ???.

15
??-??????? polymorphism

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

16
??-??????? polymorphism

• ???? ?????? ???????? ???-???????
• ????????? ????? ???? ?? ?? ??? ??????. ?????????
  ?? ???? ???? ?? ??? ?-instance ???? ??????? ????
  ??? ???? ?????? ?? ???? ????.
• ?????? ??????? ?? ????? ????????? ???? ???? ?????
  ??? ???? ????????. ????? ?? ???? ???? ?? ???????
  (????? ???????) ??????? ?-casting. ????? ?? ????
  ?-casting ????? ?? ???? ????.

17
Shapes.java

• public class Shapes
• public static void main(String args)
• Triangle tri1 new Triangle(1.0 , 1.0 , 1.0
  , "Blue")
• Triangle tri2 new EquilateralTriangle(2.0
  , "Blue")
• EquilateralTriangle tri3 new
  EquilateralTriangle(3.0 , "Blue")
• Triangle tri4 tri3
• tri1.area()
• tri2.area()
• tri3.area()
• tri4.area()
• EquilateralTriangle tri5
  (EquilateralTriangle) tri2
• tri5.area()
• EquilateralTriangle tri6
  (EquilateralTriangle) tri1

18
???? ???-???????

• ???? ??? ????? ??? ???? ????? (widening
  conversion) ????? ?"? ???? ????? ("").
• ???? ????? ??? ??? ???? ??? (narrowing
  conversion) ????? casting ?????. ??? ????? ?? ??
  ????? ????? ????? ?? ??? ???? ??.
• ??? ??????? ???????? ???-??????? ????? ???? ????.
• ?? ?????? ??? ????? ???? ????? (?? ?????) ??
  ?????, ??? ????? ?? ??? ???? ?? ???? ????? ??
  ???? ??? (?? ?? ?????? ??? ???? ?????).

19
???? ???-??????? (????)

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

class A A() int a1 static int s
1 static int s() return s int a()
return a
class B extends A B()super() int
a2 static int s 2 static int s()
return s int a() return a
20
????? ???? ?? ?????
A a1 new A(), b new B() B bb new
B() System.out.println("b.s()
"b.s()) System.out.println("bb.s()
"bb.s()) System.out.println("b.s
"b.s) System.out.println("bb.s
"bb.s) System.out.println("b.a
"b.a) System.out.println("b.a() "b.a())
?? ????? ? main ??? ?
21
????? ???? ?? ?????
A a1 new A(), b new B() B bb new
B() System.out.println("b.s()
"b.s()) System.out.println("bb.s()
"bb.s()) System.out.println("b.s
"b.s) System.out.println("bb.s
"bb.s) System.out.println("b.a
"b.a) System.out.println("b.a() "b.a())
???? ?????
b.s() 1 bb.s() 2 b.s 1 bb.s 2 b.a
1 b.a() 2
22
?????? Object

• ??? ?????? Java, ?? ????? ????? ????? ????? ????,
  ????? ?? Object.
• ????? ???? ??? ?? Object ??? ????? ??? ?? ??
  ?????.
• Object ???? ????? ????? ?????. ??????? ???? ??
  toString() , clone() ?-equals(Object).
• Object ??????? ?????? ???? ???-???????, ??????

23
???? ???

• public class SmartArray
• protected Object ar
• public SmartArray(Object ar)
• this.ar ar
• public int in(int i,Object obj)
• if ((igt0) (iltar.length))
• ari obj
• return i
• else
• return -1
• public Object out(int i)
• if ((igt0) (iltar.length))

24
???? ???

• public class PlayWithSmartArray
• public static void main(String args)
• Object obj "Yossi" , "Chaim" ,
  "Nechama"
• obj1 new EquilateralTriangle(6.0)
• SmartArray smart new SmartArray(obj)
• smart.findDuplications()
• smart.in(2,new EquilateralTriangle(6.0))
• smart.findDuplications()
• smart.in(2,smart.out(1))
• smart.findDuplications()
• New equilateral triangle crerated