接口
接口只能包含:constants, method signatures(abstract), default methods, static methods, and nested types
方法体只存在于:default methods and static methods
接口不能实例化,只能被类实现,或者被其他接口继承(接口可以多继承)。
定义接口:
public interface OperateCar {
// constant declarations, if any
// method signatures
// An enum with values RIGHT, LEFT
int turn(Direction direction,
double radius,
double startSpeed,
double endSpeed);
int changeLanes(Direction direction,
double startSpeed,
double endSpeed);
int signalTurn(Direction direction,
boolean signalOn);
int getRadarFront(double distanceToCar,
double speedOfCar);
int getRadarRear(double distanceToCar,
double speedOfCar);
......
// more method signatures
}
类实现接口:
public class OperateBMW760i implements OperateCar {
// the OperateCar method signatures, with implementation --
// for example:
public int signalTurn(Direction direction, boolean signalOn) {
// code to turn BMW's LEFT turn indicator lights on
// code to turn BMW's LEFT turn indicator lights off
// code to turn BMW's RIGHT turn indicator lights on
// code to turn BMW's RIGHT turn indicator lights off
}
// other members, as needed -- for example, helper classes not
// visible to clients of the interface
}
如果接口不是public,那么只能被同一个包里面的类实现。
实现接口
接口:
public interface Relatable {
// this (object calling isLargerThan())
// and other must be instances of
// the same class returns 1, 0, -1
// if this is greater than,
// equal to, or less than other
public int isLargerThan(Relatable other);
}
实现:
public class RectanglePlus
implements Relatable {
public int width = 0;
public int height = 0;
public Point origin;
// four constructors
public RectanglePlus() {
origin = new Point(0, 0);
}
public RectanglePlus(Point p) {
origin = p;
}
public RectanglePlus(int w, int h) {
origin = new Point(0, 0);
width = w;
height = h;
}
public RectanglePlus(Point p, int w, int h) {
origin = p;
width = w;
height = h;
}
// a method for moving the rectangle
public void move(int x, int y) {
origin.x = x;
origin.y = y;
}
// a method for computing
// the area of the rectangle
public int getArea() {
return width * height;
}
// a method required to implement
// the Relatable interface
public int isLargerThan(Relatable other) {
RectanglePlus otherRect
= (RectanglePlus)other;
if (this.getArea() < otherRect.getArea())
return -1;
else if (this.getArea() > otherRect.getArea())
return 1;
else
return 0;
}
}
对于接口:
public interface DoIt {
void doSomething(int i, double x);
int doSomethingElse(String s);
}
如果想添加新方法,为了避免影响已经实现了该接口的所有类,有以下几种方式:
①继承
public interface DoItPlus extends DoIt {
boolean didItWork(int i, double x, String s);
}
②default method
public interface DoIt {
void doSomething(int i, double x);
int doSomethingElse(String s);
default boolean didItWork(int i, double x, String s) {
// Method body
}
}
如果继承了接口,那么子接口的默认方法有可能出现:
- 无声明,继承父接口的默认方法
- 声明,变为abstract method,实现类,必须实现该方法(也就是父类默认,但是子类不默认了)
- 声明并重写,以子类的默认方法为准
③static method
public interface TimeClient {
// ...
static public ZoneId getZoneId (String zoneString) {
try {
return ZoneId.of(zoneString);
} catch (DateTimeException e) {
System.err.println("Invalid time zone: " + zoneString +
"; using default time zone instead.");
return ZoneId.systemDefault();
}
}
default public ZonedDateTime getZonedDateTime(String zoneString) {
return ZonedDateTime.of(getLocalDateTime(), getZoneId(zoneString));
}
}
接口的static method,就相当于把多个class的static method抽到了一个公共的地方,实现该接口的类,都具有static method。
接口类型
接口也可以作为类型:
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;
}
接口类型的赋值对象,必须是实现该接口的类的实例。
标签:Java,int,double,笔记,public,接口,return,method From: https://www.cnblogs.com/df888/p/17459290.html参考资料: