通用類，來繼承出圓和矩形。
package?circle;
public?class?Geometric?{
private?String?color="white";
private?boolean?filled;
private?java.util.Date?dateCreated;
public?Geometric(){
dateCreated=new?java.util.Date();
}
public?Geometric(String?color,boolean?filled){
dateCreated=new?java.util.Date();
this.filled=filled;
this.color=color;
}
public?java.util.Date?getDateCreated()
{
return?dateCreated;
}
public?String?getColor()
{
return?color;
}
public?void?setColor(String?color)
{
this.color=color;
}
public?boolean?isFilled()
{
return?filled;
}
public?void?setFilled(boolean?filled)
{
this.filled=filled;
}
public?String?toString()
{
return?"created?on"+dateCreated+"\ncolor:"+color+"and?filled?"+filled;
}
}
package?circle;
import?java.util.*;
public?class?Circle?extends?Geometric{
private?double?radius;
public?Circle()
{}
public?Circle(double?radius)
{
this.radius=radius;
}
public?Circle(double?radius,String?color,boolean?filled)
{
this.radius=radius;
setColor(color);
setFilled(filled);
}
public?double?getRadius()
{
return?radius;
}
public?void?setRadius(double?radius)
{
this.radius=radius;
}
public?double?getArea()
{
return?Math.PI*radius*radius;
}
}
package?circle;
public?class?Rectangle?extends?Geometric?{
private?double?width;
private?double?height;
public?Rectangle(){
}
public?Rectangle(double?width,double?height)
{
this.width=width;
this.height=height;
}
public?Rectangle(double?width,double?height,String?color,boolean?filled)
{
this.width=width;
this.height=height;
setColor(color);
setFilled(filled);
}
public?double?getWidth()
{
return?width;
}
public?void?setWidth(double?width)
{
this.width=width;
}
public?double?getHeight()
{
return?height;
}
public?void?setHeight(double?height)
{
this.height=height;
}
public?double?getArea()
{
return?width*height;
}
public?double?getPerimeter()
{
return?2*(width+height);
}
}
package?circle;
public?class?main?{
public?static?void?main(String[]?args)?{
/**
Geometric?g1=new?Geometric();
g1.setFilled(true);
Geometric?g2=new?Geometric("black",false);
System.out.print(g1.toString());
System.out.print(g2.toString());
*/
Circle?c1=new?Circle();
c1.setRadius(1.0);
System.out.println(c1.getArea());
Circle?c2=new?Circle(2.0,"red",true);
System.out.println(c2.getArea());
Rectangle?r1=new?Rectangle();
System.out.println(r1.getArea());
Rectangle?r2=new?Rectangle(1.0,2.0);
System.out.println(r2.getArea());
}
}
java中有兩個包時，如果在一個包中使用其他包的類，可導入，import.包名.類名;即可方便使用。
重載方法意味著可以定義多個同名的方法，但這些方法具有不同的簽名。
覆蓋方法意味著為子類中的方法提供一個全新的實現。具體例子如下：
//類A的方法P覆蓋了在類B中定義的同一個方法。
public?class?Test{
public?static?void?main(String[]?args){
A?a=new?A();
a.p(10);
a.p(10.0);
}
}
class?B{
public?void?p(double?i){
System.out.println(i*2);
}
}
class?A?extends?B{
public?void?p(double?i){
System.out.println(i);
}
}
//類B有兩個重載方法P(double?i)和P(int?i)，類B的p(double?i)方法被繼承。
public?class?Test{
public?static?void?main(String[]?args){
A?a=new?A();
a.p(10);
a.p(10.0);
}
}
class?B{
public?void?p(double?i){
System.out.println(i*2);
}
}
class?A?extends?B{
public?void?p(int?i){
System.out.println(i);
}
}
使用方法及實例講解)
