Java基础：继承

示例代码：

class TwoDShapes{
private double width;
private double height;
//width 和 height的访问器方法
double getWidth(){
return width;
}
double getHeight(){
return height;
}
void setWidth(double w){
width = w;
}
void setHeight(double h){
height = h;
}
//父类构造方法
TwoDShapes(double w,double h){
width = w;
height = h;
}
void showDim(){
System.out.println("width and height:"+ width +"and"+ height);
}
}
class Triangel extends TwoDShapes{ //通过extends关键字继承
String style;
Triangel(String sty,double w,double h){ //子类构造方法,初始化对象的变量和继承TwoDShapes的width,height
style = sty;
setWidth(w);
setHeight(h);
}
//或者
Triangel(String sty,double w,double h){ //子类构造方法,super()调用父类构造
super(w,h);
style = sty;
}
double area(){
//return width * height /2; //引用TwoDShapes的成员，不能访问private修饰的成员
return getWidth()*getHeight()/2; //private 成员，可以通过访问器方法访问。
}
void showStyle(){
System.out.println("style:"+ style);
}
}
class Shapes{
public static void main(String args[]){
Triangel t1 = new Triangel();
Triangel t2 = new Triangel();
t1.width = 4; //普通赋值width,height 是public修饰
t1.height =4;
t1.style ="filled";
t2.setWidth(8.0); //通过访问器方法设置，width,height是private修饰
t2.setHeight(12.0);
t2.style ="outlined";
System.out.println("t1:");
t1.showDim();
t1.showStyle();
System.out.println("t1.area:"+ t1.area());
System.out.println("t2:");
t2.showDim();
t2.showStyle();
System.out.println("t2.area:"+ t2.area());
Triangel t3 = new Triangel("filled",4.0,4.0); //通过子类方法构建对象
System.out.println("t3:");
t3.showDim();
t3.showStyle();
System.out.println("t3.area:"+ t3.area());
}
}

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使用super调用父类成员：

class A{
int i;
}
class B extends A{
int i;
B(int a,int b){
super.i = a; //调用父类i
i = b;
}
void show(){
System.out.println("super.i:"+ super.i);
System.out.println("subclass.i:"+ i);
}
}
class UseSuper{
public static void main(String args[]){
B ob = new B(1,2);
ob.show();
}
}

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