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Giao din
GV. Trn Trng Hiu Bi 4. Giao din
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Ni dung
nh ngha mt giao din
Thc thi mt giao din
Dng giao din nh mt kiu
Vit li giao din
V d
GV. Trn Trng Hiu Bi 4. Giao din
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nh ngha mt giao din
Cc giao din c dng m ha nhng im ging nhau m cc lp ca cc kiu khc
nhau cng c tuy nhng khng nht thit phi cha mt quan h lp.
V d: Mt ngi v mt con vt cng c th hut so. iu khng c
ngha nn biu din lp Ngi v lp Vt l cc lp con ca lp i
tng Hut_so.
Mt ngi v mt hnh ch nht u c th o mt s kch thc, tuy
nhin khng nn xp hai i tng ny vo cng mt lp i tng
no c
GV. Trn Trng Hiu Bi 4. Giao din
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nh ngha mt giao din
Trong ngn ng OPP, mt giao din c c t bng mt
kiu tru tng.
Mt giao din ch bao gm:
Cc ch k phng thc (nguyn mu)
Cc khai bo hng
public interface Relatable {
public int isLargerThan(Relatable other);
}
GV. Trn Trng Hiu Bi 4. Giao din
Mt kiu tru tng thun ty
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nh ngha mt giao din
Mt giao din c th c m rng t mt giao din khc:
public interface GroupedInterface extends
Interface1, Interface2, Interface3 {
double E = 2.718282;
void doSomething(int i, double x);
int doSomthingElse(String s);
}
Vy GroupedInterface c bao nhiu ch k phng thc?
GV. Trn Trng Hiu Bi 4. Giao din
Mt hng s
Hai ch k phng thc
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Thc thi mt giao din
Giao din khng th c khi to.
Relatable relatable = new Relatable(); SAI
Ti sao?
Bi v mt giao din l mt kiu tru tng v ta khng th to ra
mt i tng tru tng.
GV. Trn Trng Hiu Bi 4. Giao din
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Thc thi mt giao din
Mt lp m thc thi mt giao din th n phi thc thi tt
c cc phng thc c m t trong giao din .
Mt lp tru tng m thc thi mt giao din th n c th
ch cn thc thi mt s phng thc c nh ngha bi
giao din.
Cc phng thc m cha c thc thi phi c thc thi cc
lp con ca lp tru tng .
GV. Trn Trng Hiu Bi 4. Giao din
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Thc thi mt giao din
public class Person implements Relatable {
private double weight;
public Person(double w) {
weight = w;
}
public double getWeight() {
return weight;
}
public int isLargerThan(Relatable other) {
Person person = (Person) other;
if (this.getWeight() < person.getWeight())
return -1;
else if (this.getWeight() > person.getWeight())
return 1;
else
return 0;
}
}
GV. Trn Trng Hiu Bi 4. Giao din
Thc thi phng thc c m t
trong giao din Relatable.
Ch ton t p kiu
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Thc thi mt giao din
public class Rectangle implements Relatable {
private int width = 0;
private int height = 0;
private Point origin;
public Rectangle(Point p, int w, int h) {
origin = p;
width = w;
height = h;
}
public int getArea() {
return width * height;
}
public int isLargerThan(Relatable other) {
Rectangle otherRect = (Rectangle) other;
if (this.getArea() < otherRect.getArea())
return -1;
else if (this.getArea() > otherRect.getArea())
return 1;
else
return 0;
}
}
GV. Trn Trng Hiu Bi 4. Giao din
Thc thi phng thc bt buc so
snh hai hnh ch nht.
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S dng mt giao din
Mt giao din c dng nh mt kiu.
Nu ta nh ngha mt bin m kiu ca n l mt giao
din th i tng m ta gn cho bin ny phi l mt hin
thc ca mt lp m thc thi giao din .
Relatable person = new Person(50.5);
Relatable rectangle = new Rectangle(new Point(5,
5), 20, 40);
Relatable a;
a = new A();
GV. Trn Trng Hiu Bi 4. Giao din
Khai bo ny li nu lp A khng thc thi
giao din Relatable.
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S dng mt giao din
Mt phng thc tm i tng ln hn trong hai i tng
kiu Relatable: public Object findLargest(Object object1,
Object object2) { Relatable obj1 = (Relatable) object1;
Relatable obj2 = (Relatable) object2; if ((obj1).isLargerThan(obj2)
> 0) return object1; else
return object2;
}
GV. Trn Trng Hiu Bi 4. Giao din
Phng thc ny cho php so snh hai i
tng kiu Person hay hai i tng kiu Rectangle.
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Vit li giao din
Xt mt giao din nh sau:
public interface DoIt {
void doSomething(int i, double x);
int doSomethingElse(String s);
}
Cc ngi dng khc to ra cc thc thi khc nhau ca giao
din ny
H to ra ba lp A, B, C cng thc thi DoIT.
GV. Trn Trng Hiu Bi 4. Giao din
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Vit li giao din
Gi s sau mt thi gian ta mun thm mt phng thc mi cho DoIt:
public interface DoIt {
void doSomething(int i, double x);
int doSomethingElse(String s);
boolean didItWork(int i, double x, String s);
}
iu ny lm tt c cc lp thc thi giao din DoIt b hng. Cc lp
A, B, C khng cn lm vic c na.
Ti sao? Bi v cc lp ny khng thc thi giao din na.
Nhng lp trnh vin tin tng vo giao din ny s phn i n hon ton.
GV. Trn Trng Hiu Bi 4. Giao din
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Vit li giao din
Ta nn to giao din DoItPlus l m rng ca DoIt.
By gi nhng ngi khc c th la chn tip tc dng
DoIt hay nng cp ln DoItPlus.
public interface DoItPlus extends DoIt {
boolean didItWork(int i, double x, String s);
}
GV. Trn Trng Hiu Bi 4. Giao din
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Mt s v d khc v giao din
/**
* Describes an interface for any class whose
* objects can be measured.
*/
public interface Measurable {
/**
* Gets the measure of the object.
* @return a double
*/
double getMeasure();
}
Ta nn lm th no nu mun m hnh th g m c th o
c?
GV. Trn Trng Hiu Bi 4. Giao din
Ti liu v giao din
Ti liu v phng thc
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Mt s v d khc v giao din
/**
* Describes any class whose objects * can measure other objects.
*/ public interface Measurer { /** * Computes the measure of an
object. * * @param anObject * the object to be measured * * @return
the measure of the object. */ double measure(Object anObject);
}
GV. Trn Trng Hiu Bi 4. Giao din
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Mt s v d khc v giao din
/**
* This interface imposes a total ordering on the objects of
* each class that implements it.
*/
public interface Comparable {
/**
* Compares this object with the specified object for order.
*
* @param o the object to be compared.
* @return a negative integer, zero, or a positive integer
* as this object is less than, equal to, or greater
* than the specified object.
*/
int compareTo(T o);
}
GV. Trn Trng Hiu Bi 4. Giao din
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Mt s v d khc v giao din
/**
* A predator can chase and eat preys. */ public interface
Predator { /** * Chases a prey p. * @param p a prey * @return true
if success, false if failure. */ boolean chasePrey(Prey p); /** *
Eats a prey. * @param p a prey */ void eatPrey(Prey p); }
GV. Trn Trng Hiu Bi 4. Giao din
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Mt s v d khc v giao din
/**
* A lion is a super predator.
*/
public class Lion implements Predator {
public boolean chasePrey(Prey p) {
// implement to chase prey p (specifically for a lion)
}
public void eatPrey(Prey p) {
// implement to eat prey p (specifically for a lion)
}
}
GV. Trn Trng Hiu Bi 4. Giao din
/**
* A frog can be a predator or a prey.
*/
public class Frog implements Predator, Prey {
// implement methods of the two interfaces here...
}
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Mt s v d khc v giao din
/**
* A venomous predator.
*/
public interface VenomousPredator extends Predator,
Venomous{
// interface body
}
GV. Trn Trng Hiu Bi 4. Giao din
/**
* A snake is a venomous predator and it can be prey.
*/
public class Snake implements VenomousPredator, Prey {
// implement methods of the two interfaces here
}
