JAVA课没好好听，书上没例题看不懂，貌似接口这东西很弱智啊……但我怎么就是弄不出来啊！！
interface Exchange{
public double area();
public void girth();
}
abstract class Shape{
abstract protected double area();
abstract protected void girth();
}
class Rectangle extends Shape implements Exchange{
float width,length;
Rectangle(float w,float l){
width=w;
length=l;
}
public double area(){
return width*length;
}
public void girth(){
double g=(width+length)*2;
System.out.println("and the girth is:"+g);
}
}
class Circle extends Shape implements Exchange{
float radius;
Circle(float r){
radius=r;
}
public double area(){
return radius*radius*3.14;
}
public void girth(){
double g=radius*2*3.14;
System.out.println("and the girth is:"+g);
}
}
public class Shape_ex_2 { /**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Exchange rc=new Rectangle(6,12);
Exchange cir=new Circle(4);
System.out.println("Rectangle's area is:"+rc.area());
rc.girth();
System.out.println("Circle's area is:"+cir.area());
cir.girth();
} }

题目是把下面这个改成用接口的
abstract class Shape{
abstract protected double area();
abstract protected void girth();
}
class Rectangle extends Shape{
float width,length;
Rectangle(float w,float l){
width=w;
length=l;
}
public double area(){
return width*length;
}
public void girth(){
double g=(width+length)*2;
System.out.println("and the girth is:"+g);
}
}
class Circle extends Shape{
float radius;
Circle(float r){
radius=r;
}
public double area(){
return radius*radius*3.14;
}
public void girth(){
double g=radius*2*3.14;
System.out.println("and the girth is:"+g);
}
}
public class Shape_ex { /**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Rectangle rc=new Rectangle(6,12);
Circle cir=new Circle(4);
System.out.println("Rectangle's area is:"+rc.area());
rc.girth();
System.out.println("Circle's area is:"+cir.area());
cir.girth();
} }

被吞了……………………
题目是把下面这个改成用接口的
abstract class Shape{
abstract protected double area();
abstract protected void girth();
}
class Rectangle extends Shape{
float width,length;
Rectangle(float w,float l){
width=w;
length=l;
}
public double area(){
return width*length;
}
public void girth(){
double g=(width+length)*2;
System.out.println("and the girth is:"+g);
}
}
class Circle extends Shape{
float radius;
Circle(float r){
radius=r;
}
public double area(){
return radius*radius*3.14;
}
public void girth(){
double g=radius*2*3.14;
System.out.println("and the girth is:"+g);
}
}
public class Shape_ex { /**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Rectangle rc=new Rectangle(6,12);
Circle cir=new Circle(4);
System.out.println("Rectangle's area is:"+rc.area());
rc.girth();
System.out.println("Circle's area is:"+cir.area());
cir.girth();
} }

以下是一个建立矩形和圆，并输出它们相应面积和周长的程序。
改写成用接口来实现类之间的连接，做一些小改动，但程序功能不变——
abstract class Shape{
abstract protected double area();
abstract protected void girth();
}
class Rectangle extends Shape{ //矩形类的构建方法
float width,length;
Rectangle(float w,float l){
width=w; //矩形的宽
length=l; //矩形的长
}
public double area(){
return width*length; //运算出矩形的面积
}
public void girth(){
double g=(width+length)*2;
System.out.println("and the girth is:"+g); //运算并输出矩形的周长
}
}
class Circle extends Shape{ //圆类的构建方法
float radius;
Circle(float r){
radius=r; //圆的半径
}
public double area(){
return radius*radius*3.14; //运算出圆的面积
}
public void girth(){
double g=radius*2*3.14; //运算出圆的周长
System.out.println("and the girth is:"+g);
}
}
public class Shape_ex { /**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Rectangle rc=new Rectangle(6,12); //建立新的矩形，宽为6，长为12
Circle cir=new Circle(4); //建立新的圆，半径是4
System.out.println("Rectangle's area is:"+rc.area()); //输出矩形面积
rc.girth();
System.out.println("Circle's area is:"+cir.area()); //输出圆面积
cir.girth();
} }