05 Kế thừa trong java

7/31/2019 05 K tha trong java

1/30


2/30

K tha 2Nguy n Vit H

Ni dung

V

n

s

d

ng l

iS dng li bng k thaK tha trong Java

nh ngh a lp k thathm ph ng th c, thu c tnhkim sot truy c pconstructor

Lp Object


3/30

K tha 3Nguy n Vit H

Ti liu tham kh o

Thinking in Java , chapter 6Java how to program , chapter 9


4/30

K tha 4Nguy n Vit H

S dng li

Tn ti nhiu loi i tng c cc thu ctnh v hnh vi t ng t hoc lin quann nhau

Person, Student, Manager,Xut hin nhu c u s dng li cc mngu n vit

S

d

ng l

i thng qua copyS dng li thng qua quan h has_aS dng li thng qua c ch k tha


5/30

K tha 5Nguy n Vit H

S dng liCopy m ngu n

Tn cng, d nhmKh s a li do t n ti nhiu phin b n

Quan h has_aS dng lp c nh l thnh ph n ca lpmi

S dng li ci t vi giao di n miPh i vit li giao di nCha mm d o


6/30

K tha 6Nguy n Vit H

V d: has_aclass Person {

private String name; private Date bithday; public String getName() { return name; }

...}class Employee {

private Person me; private double salary; public String getName() { return me.getName(); }

...}


7/30

K tha 7Nguy n Vit H

class Manager {

private Employee me; private Employee assistant; public setAssistant(Employee e) {...}

...}...

Manager junior = new Manager(); Manager senior = new Manager();

senior.setAssistant(junior); // error


8/30

K tha 8Nguy n Vit H

K tha

Da trn quan h is_aTha h ng li cc thu c tnh v ph ngthc c

Chi tit ha cho ph h p vi mc ch s dng m i

Thm cc thu c tnh m iThm ho c hiu ch nh cc ph ng th c


9/30

K tha 9Nguy n Vit H

Thu t ng

K thaLp c s, lp chaLp dn xu t, lp con


10/30

K tha 10Nguy n Vit H

K tha trong Java[public] class DerivedClass extends BaseClass {

/* new features goes here */}

V d :

class Employee extends Person { private double salary; public boolean setSalary(double sal) {

...salary = sal;

return true;}}


11/30


Employee e = new Employee();

e.setName("John");e.setSalary(3.0);

Person-name

-birthday

+setName()

+setBirthday()

Employee

-salary

+setSalary()+getDetail()


12/30


private membersclass Employee extends Person {

... public String getDetail() {

String s;// s = name + "," + birthday;s = getName() + "," + getBirthday();s += "," + salary;return s;

}}


13/30


Mc truy c p protected

m bo che d u thng tin, thngthng cc thu c tnh c khai bo lprivate

i tng thu c lp dn xu t phi truy c p tichng thng qua cc ph ng th c get v set.

Mc truy c p protected gi i quyt vn ny

i tng c a lp dn xu t truy c p ccc protected members ca lp c sCc i tng khc khng truy c p c


14/30


public class Person { protected Date birthday; protected String name;

...}

public class Employee extends Person {...

public String getDetail() {String s;s = name + "," + birthday;s += "," + salary;return s;

}}


15/30


Cc m c kim sot truy c p

YesYesYesYespublic

YesYesYesprotected

YesYespackage( default )

Yesprivate

UniverseSubclassSame packageSameclass Modifier


16/30


Trong cng gi public class Person {Date birthday;String name;

...}

public class Employee extends Person {...

public String getDetail() {String s;s = name + "," + birthday;s += "," + salary;return s;

}}


17/30


Khc gi package abc;

public class Person { protected Date birthday; protected String name;

...

}

import abc.Person; public class Employee extends Person {


String s;s = name + "," + birthday;s += "," + salary;return s;

}}


18/30


nh ngh a li cc ph ng th cChng ta c th nh ngh a li cc ph ngthc ca lp c si tng c a lp dn xu t s hot ng

vi phng th c mi ph h p vi nC th ti s dng ph ng th c cng tnca lp c s bng t kha super


19/30


V d package abc;

public class Person { protected Date birthday; protected String name; public String getDetail() {...}

...}

import abc; public class Employee extends Person {


String s;s = super.getDetail() + "," + salary;

return s;}

}


20/30


nh ngh a li phng th cPh i c quy n truy c p khng cht hnphng th c c nh ngh a liPh i c kiu gi tr tr li nh nhau


21/30


class Parent { public void doSomething() {} public int doSomething2() {

return 0;}

}

class Child extends Parent { protected void doSomething() {} public void doSomething2() {}

}


22/30


Tha k nhiu tngPerson

-name

-birthday

+setName

+setBirthday

Employee

-salary

+setSalary

+getDetail

Manager

-rank...

Programmer

-project

...

Student

-id

...

Mi i tng utha k t lp g c Object


23/30


Constructor

Lp d n xu t k tha m i thuc tnh vphng th c c a lp c sKhng k th a ph ng th c kh i t o

C hai gi i php g i constructor c a lpc s

s dng constructor m c nhgi constructor c a lp c s mt cch t ngminh


24/30


class Point {

protected int x, y; public Point() {} public Point(int xx, int yy) {

x = xx;

y = yy;}

}

class Circle extends Point { protected int radius;

public Circle() {}}

Point p = new Point(10, 10);Circle c1 = new Circle();Circle c2 = new Circle(10, 10); // erorr


25/30


Gi constructor c a lp c s

Vic khi to thu c tnh c a lp c s nngiao ph cho constructor c a lp c sS dng t kha super gi

constructor c a lp c sConstructor c a lp c s bt buc ph ic thc hin u tin

Nu lp c s khng c constructor m c nhth b t bu c ph i gi constructor t ng minh


26/30


class Point {


x = xx;

y = yy;}

}

class Circle extends Point { protected int radius; public Circle() {} public Circle(int xx, int yy, int r) {

super(xx, yy);radius = r;

}}


27/30


class Point {

protected int x, y; public Point(int xx, int yy) {

x = xx;y = yy;

}}

class Circle extends Point {

protected int radius; public Circle() { super(0, 0); } public Circle(int xx, int yy, int r) {

super(xx, yy);

radius = r;}

}


28/30


class Point {


x = xx;

y = yy;}

}

class Circle extends Point { protected int radius; public Circle() { } public Circle(int xx, int yy, int r) {

// super(xx, yy);radius = r;

}}


29/30


Th t khi toclass Point { protected int x, y; public Point() {

System.out.println("Point constructor");}

}class Circle extends Point {

protected int radius; public Circle() {

System.out.println("Circle constructor");}

}...Circle c = new Circle();


30/30


T kha finalThu c tnh final

hng s , ch c gn gi tr khi to m t ln, khngthay i c gi tr

Ph ng th c final

khng cho php nh ngh a li lp d n xu tTham s final

khng thay i c gi tr ca tham chi u

Lp finalkhng nh ngh a c lp d n xu t

Documents

05 Kế thừa trong java