from other classes, thereby inheriting fields and methods from
those classes:class Sub extends Sup {
…
}
*
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Презентация на тему 4. Java OOP. 4. Inheritance and Polymorphism
Содержание
- 2. Inheritance Basics (1 of 3)Classes can be
- 3. Inheritance Basics (2 of 3)A class that
- 4. Inheritance Basics (3 of 3)A subclass inherits
- 5. Members InheritanceA subclass inherits all of the
- 6. Fields InheritanceThe inherited fields can be used
- 7. What will be the output?class A{
- 8. What will be the output?class A{
- 9. What will be the output?class A{
- 10. What will be the output?class A{
- 11. What will be the output?class A{
- 12. What will be the output?class A{
- 13. Methods InheritanceThe inherited methods can be used
- 14. What will be the output?class A{
- 15. What will be the output?class A{
- 16. Methods Overriding and HidingYou can write a
- 17. Constructors CallYou can write a subclass constructor
- 18. Private Members in a SuperclassA subclass does
- 19. Exercise 4.4.1: DepoBase classModify 433DepoMonthCapitalize, 432DepoBarrier, and
- 20. DepoBase Class (1 of 2)public class DepoBase
- 21. DepoBase Class (2 of 2)// accessorspublic double
- 22. DepoSimple Classpublic class DepoSimple extends DepoBase{ public DepoSimple(){
- 23. Exercise 4.4.1: DepoBase classSee 441DepoBase projects for the full text*Infopulse Training Center
- 24. Casting Objects (1 of 3)Casting shows the
- 25. Casting Objects (2 of 3)We can tell
- 26. Casting Objects (3 of 3) You can
- 27. What will be the output?class A{
- 28. What will be the output?class A{
- 29. What will be the output?class A{
- 30. What will be the output?class A{
- 31. What will be the output?class A{
- 32. What will be the output?class A{
- 33. What will be the output?class A{
- 34. What will be the output?class A{
- 35. Overriding Instance Methods IAn instance method in
- 36. Overriding Instance Methods IIWhen overriding a method,
- 37. What will be the output?class A{
- 38. What will be the output?class A{
- 39. Hiding Static Methods (1 of 6)public class
- 40. Hiding Static Methods (2 of 6)public class
- 41. Hiding Static Methods (3 of 6)public static
- 42. Hiding Static Methods (4 of 6)Output:The instance
- 43. Hiding Static Methods (5 of 6)public static
- 44. Hiding Static Methods (6 of 6)Output:The class
- 45. Polymorphism (1 of 2)Connecting a method call
- 46. Polymorphism (2 of 2)All method binding in
- 47. Exercise 4.4.2Create a deposit array of different
- 48. Exercise: Interest Values SumDate start = new
- 49. Exercise: Interest Values Sumdouble sum = 0.0; for(DepoBase
- 50. Exercise : Interest Values SumSee 442InterestSum or 442aInterestSum project for the full text*Infopulse Training Center
- 51. Hiding FieldsWithin a class, a field that
- 52. Subclass Constructors (1 of 2)The syntax for
- 53. Subclass Constructors (2 of 2)If a constructor
- 54. Accessing Superclass MembersIf your method overrides one
- 55. Writing Final MethodsYou use the final keyword
- 56. Final ClassesYou can declare an entire class
- 57. Скачать презентацию
- 58. Похожие презентации
Inheritance Basics (1 of 3)Classes can be derived from other classes, thereby inheriting fields and methods from those classes: class Sub extends Sup { … }*Infopulse Training Center
![Hiding Static Methods (3 of 6)public static void main(String[] args) { Animal](/img/tmb/15/1445022/241573593c36bdea2a1b655cb5ad5756-720x.jpg "4. Java OOP. 4. Inheritance and Polymorphism")
![Hiding Static Methods (5 of 6)public static void main(String[] args) { Animal](/img/tmb/15/1445022/6311a69cf86039a0047175dda9e8ae1c-720x.jpg "4. Java OOP. 4. Inheritance and Polymorphism")
![Exercise: Interest Values SumDate start = new GregorianCalendar(2013, Calendar.SEPTEMBER, 8).getTime();DepoBase[] depo =](/img/tmb/15/1445022/8e05507010855bbb7c665ba861c11cd3-720x.jpg "4. Java OOP. 4. Inheritance and Polymorphism")
Слайд 2
Inheritance Basics (1 of 3)
Classes can be derived
class Sub extends Sup {
…
}
Слайд 3
Inheritance Basics (2 of 3)
A class that is
derived from another class is called a subclass (also
a derived class, extended class, or child class).The class from which the subclass is derived is called a superclass (also a base class or a parent class).
Every class has one and only one direct superclass (single inheritance).
Class Object is exception, it is a root class
*
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Слайд 4
Inheritance Basics (3 of 3)
A subclass inherits all
the members (fields, methods, and nested classes) from its
superclassConstructors are not members, so they are not inherited by subclasses
The constructor of the superclass can be invoked from the subclass
*
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Слайд 5
Members Inheritance
A subclass inherits all of the public
and protected members of its parent, no matter what
package the subclass is in.If the subclass is in the same package as its parent, it also inherits the package-private members of the parent.
You can use the inherited members as is, replace them, hide them, or supplement them with new members
*
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Слайд 6
Fields Inheritance
The inherited fields can be used directly
You
can declare a field in the subclass with the
same name as the one in the superclass, thus hiding it (not recommended).You can declare new fields in the subclass that are not in the superclass.
*
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Слайд 7
What will be the output?
class A{
int
v1 = 8;
protected double p = -5.0;
private String s = “1234”;}
class B extends A{
public void doSomething(){
System.out.println(s);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}
Слайд 8
What will be the output?
class A{
int
v1 = 8;
protected double p = -5.0;
private String s = “1234”;}
class B extends A{
public void doSomething(){
System.out.println(s);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}
Compilation error
Слайд 9
What will be the output?
class A{
int
v1 = 8;
protected double p = -5.0;
private String s = “1234”;}
class B extends A{
public void doSomething(){
System.out.println(p);
}
*
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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}
Слайд 10
What will be the output?
class A{
int
v1 = 8;
protected double p = -5.0;
private String s = “1234”;}
class B extends A{
public void doSomething(){
System.out.println(p);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}
-5.0
Слайд 11
What will be the output?
class A{
int
v1 = 8;
protected double p = -5.0;
private String s = “1234”;}
class B extends A{
public void doSomething(){
System.out.println(v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}
Слайд 12
What will be the output?
class A{
int
v1 = 8;
protected double p = -5.0;
private String s = “1234”;}
class B extends A{
public void doSomething(){
System.out.println(v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}
8 if B and A in the same package; Compilation error otherwise
Слайд 13
Methods Inheritance
The inherited methods can be used directly
as they are.
You can declare new methods in the
subclass that are not in the superclass.*
Infopulse Training Center
Слайд 14
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
obj.doSomething();
}
}
Слайд 15
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
obj.doSomething();
}
}
8 16
Слайд 16
Methods Overriding and Hiding
You can write a new
instance method in the subclass that has the same
signature as the one in the superclass, thus overriding it.You can write a new static method in the subclass that has the same signature as the one in the superclass, thus hiding it.
*
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Слайд 17
Constructors Call
You can write a subclass constructor that
invokes the constructor of the superclass, either implicitly or
by using the keyword super.*
Infopulse Training Center
Слайд 18
Private Members in a Superclass
A subclass does not
inherit the private members of its parent class.
However,
if the superclass has public or protected methods for accessing its private fields, these can also be used by the subclass.*
Infopulse Training Center
Слайд 19
Exercise 4.4.1: DepoBase class
Modify 433DepoMonthCapitalize, 432DepoBarrier, and 431SimpleDepo
projects with help of ancestor DepoBase class (should contain
all common elements – fields and methods)*
Infopulse Training Center
Слайд 20
DepoBase Class (1 of 2)
public class DepoBase {
protected
Date startDate;
protected int dayLong;
protected double sum;
protected double interestRate;
public DepoBase()
{}public DepoBase(Date startDate, int dayLong, double sum,
double interestRate){
this.startDate = startDate;
this.dayLong = dayLong;
this.sum = sum;
this.interestRate = interestRate; }
Слайд 21
DepoBase Class (2 of 2)
// accessors
public double calculateInterest(LocalDate
start, LocalDate maturity){
int startYear = start.getYear();
int maturityYear = maturity.getYear();
. . . . . . . . . .double dayCf = start.until(maturity, ChronoUnit.DAYS)
+ 1;
double interest = sum * (interestRate / 100.0) *
(dayCf / daysInYear);
return interest;
}
Слайд 22
DepoSimple Class
public class DepoSimple extends DepoBase{
public DepoSimple(){
}
public DepoSimple(Date startDate, int dayLong, double sum, double interestRate){
super(startDate,
dayLong, sum, interestRate);}
public double getInterest(){
double interest = 0.0;
. . . . . . . . . . . .
return interest;
}
*
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Слайд 23
Exercise 4.4.1: DepoBase class
See 441DepoBase projects for the
full text
*
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Слайд 24
Casting Objects (1 of 3)
Casting shows the use
of an object of one type in place of
another type, among the objects permitted by inheritance:Object obj = new ClassName();
If, on the other hand, we write
ClassName cn = obj;
we would get a compile-time error because
obj is not known to the compiler to be a
ClassName
*
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Слайд 25
Casting Objects (2 of 3)
We can tell the
compiler to assign a ClassName to obj by explicit
casting: ClassName cn = (ClassName)obj;This cast inserts a runtime check that obj is assigned a ClassName so that the compiler can safely assume that obj is a ClassName
If obj is not a ClassName at runtime, a ClassCastException will be thrown.
*
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Слайд 26
Casting Objects (3 of 3)
You can make
a logical test as to the type of a
particular object using the instanceof operator:if (obj instanceof ClassName) {
ClassName myBike = (ClassName)obj;
}
The test x instanceof C does not generate an exception if x is null. It simply returns false.
*
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Слайд 27
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
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Class C{
public static void main(String[] args) {
A obj = new B();
obj.printV1();
obj.doSomething();
}
}
Слайд 28
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
A obj = new B();
obj.printV1();
obj.doSomething();
}
}
Compilation error “Undefined method” on line obj.doSomething();
Слайд 29
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
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Class C{
public static void main(String[] args) {
B obj = new A();
obj.printV1();
obj.doSomething();
}
}
Слайд 30
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new A();
obj.printV1();
obj.doSomething();
}
}
Compilation error “Type mismatch” on line B obj = new A();
Слайд 31
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = (B)new A();
obj.printV1();
obj.doSomething();
}
}
Слайд 32
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
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Class C{
public static void main(String[] args) {
B obj = (B)new A();
obj.printV1();
obj.doSomething();
}
}
Runtime error “ClassCastException” on line B obj = (B)new A();
Слайд 33
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
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Class C{
public static void main(String[] args) {
B obj = new B();
A objA = obj;
objA.printV1();
}
}
Слайд 34
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void doSomething(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
A objA = obj;
objA.printV1();
}
}
8
Слайд 35
Overriding Instance Methods I
An instance method in a
subclass with the same signature and return type as
an instance method in the superclass overrides the superclass's methodThe overriding method has the same name, number and type of parameters, and return type as the method it overrides.
An overriding method can also return a subtype of the type returned by the overridden method. This is called a covariant return type.
*
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Слайд 36
Overriding Instance Methods II
When overriding a method, you
might want to use the @Override annotation that instructs
the compiler that you intend to override a method in the superclass.The access specifier for an overriding method can allow more, but not less, access than the overridden method (protected to public, but not to private)
*
Infopulse Training Center
Слайд 37
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void printV1(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
}
}
Слайд 38
What will be the output?
class A{
int
v1 = 8;
protected void printV1(){
System.out.println(v1);
}}
class B extends A{
public void printV1(){
System.out.println(2 * v1);
}
*
Infopulse Training Center
Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
}
}
16
Слайд 39
Hiding Static Methods (1 of 6)
public class Animal
{
public static void testClassMethod() {
System.out.println("The class method
in Animal."); }
public void testInstanceMethod() {
System.out.println("The instance method in Animal.");
}
}
*
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Слайд 40
Hiding Static Methods (2 of 6)
public class Cat
extends Animal {
public static void testClassMethod() {
System.out.println("The
class method in Cat."); }
public void testInstanceMethod() {
System.out.println("The instance method in Cat.");
}
}
*
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Слайд 41
Hiding Static Methods (3 of 6)
public static void
main(String[] args) {
Animal myAnimal = new Animal();
Animal myAnimalCat = new Cat();Cat myCat = new Cat();
myAnimal.testInstanceMethod();
myAnimalCat.testInstanceMethod();
myCat.testInstanceMethod();
}
*
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Слайд 42
Hiding Static Methods (4 of 6)
Output:
The instance method
in Animal
The instance method in Cat
The instance method in
Cat*
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Слайд 43
Hiding Static Methods (5 of 6)
public static void
main(String[] args) {
Animal myAnimal = new Animal();
Animal myAnimalCat = new Cat();Cat myCat = new Cat();
myAnimal.testClassMethod();
myAnimalCat.testClassMethod();
myCat. testClassMethod();
}
*
Infopulse Training Center
Слайд 44
Hiding Static Methods (6 of 6)
Output:
The class method
in Animal.
The class method in Animal.
The class method in
Cat.*
Infopulse Training Center
Слайд 45
Polymorphism (1 of 2)
Connecting a method call to
a method body is called binding
When binding is performed
before the program is run (e.g. by the compiler), it’s called early binding. Late binding means that the binding occurs at run time, based on the type of object
There must be some mechanism to determine the type of the object at run time and to call the appropriate method
*
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Слайд 46
Polymorphism (2 of 2)
All method binding in Java
uses late binding unless the method is static or
final (private methods are implicitly final)You can write your code to talk to the base class and know that all the derived-class cases will work correctly using the same code
Typical example: create an array of Base class and fill it with subclasses objects. Then you can call the same method for each object from array elements
*
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Слайд 47
Exercise 4.4.2
Create a deposit array of different types
and calculate sum of their interest values
*
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Sum
= 1763.41
Слайд 48
Exercise: Interest Values Sum
Date start = new GregorianCalendar(2013,
Calendar.SEPTEMBER, 8).getTime();
DepoBase[] depo = new DepoBase[6];
depo[0] = new DepoSimple(start,
20, 1000.0, 15.0);depo[1] = new DepoSimple(start, 20, 2500.0, 18.0);
depo[2] = new DepoBarrier(start, 40, 15000.0, 11.5);
depo[3] = new DepoBarrier(start, 80, 5000.0, 14.0);
depo[4] = new DepoMonthCapitalize(start, 180, 2000.0, 16.5);
depo[5] = new DepoMonthCapitalize(start, 91, 40000.0, 12.1);
*
Infopulse Training Center
Слайд 49
Exercise: Interest Values Sum
double sum = 0.0;
for(DepoBase d:
depo) sum += d.getInterest();
sum = Math.round(sum * 100) /
100.0;if (sum == 1763.41) System.out.println("Test is true");
else System.out.println("Test failed");
}
*
Infopulse Training Center
Слайд 50
Exercise : Interest Values Sum
See 442InterestSum or 442aInterestSum
project for the full text
*
Infopulse Training Center
Слайд 51
Hiding Fields
Within a class, a field that has
the same name as a field in the superclass
hides the superclass's field, even if their types are differentHided field in the superclass can be accessed through super keyword
Hiding fields is not recommended as it makes code difficult to read
*
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Слайд 52
Subclass Constructors (1 of 2)
The syntax for calling
a superclass constructor is
super(); or: super(parameter list);
Invocation
of a superclass constructor must be the first line in the subclass constructor.*
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Слайд 53
Subclass Constructors (2 of 2)
If a constructor does
not explicitly invoke a superclass constructor, the Java compiler
automatically inserts a call to the no-argument constructor of the superclassIf the super class does not have a no-argument constructor, you will get a compile-time error
*
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Слайд 54
Accessing Superclass Members
If your method overrides one of
its superclass's methods, you can invoke the overridden method
through the use of the keyword super*
Infopulse Training Center
Слайд 55
Writing Final Methods
You use the final keyword in
a method declaration to indicate that the method cannot
be overridden by subclassesYou might wish to make a method final if it has an implementation that should not be changed and it is critical to the consistent state of the object
Methods called from constructors should generally be declared final
If a constructor calls a non-final method, a subclass may redefine that method with surprising or undesirable results
*
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Слайд 56
Final Classes
You can declare an entire class final
A
class that is declared final cannot be subclassed
This is
particularly useful, for example, when creating an immutable class like the String class.*
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