填空题 阅读以下说明和Java程序，将应填入 (n) 处的字句写在对应栏内
[说明]
以下程序的功能时三角形、矩形和正方形的面积输出。
程序由5个类组成：areatest是主类，类Triangle，Rectangle和Square分别表示三角形、矩形和正方形，抽象类Figure提供了一个计算面积的抽象方法。
[Java程序]
public class areatest
public static viod main(string args[])
Figure[]Figures=
New triangle(2,3,3),new rectangle(5,8),new square(5)
;
for(int i=0; i＜Figures.length;i++)
system.out.println(Figures+"area="+Figures.getarea());



public abstract class figure
public abstract double getarea();

public class rectangle extends (1)
double height;
double width;
public rectangle (double height,double width)
this.height=height;
this.width=width;

public string tostring()
return"rectangle:height="+height+",width="+width+":";

public double getarea()
return (2)


public class square exends (3)

public square(double width)
(4) ;

public string tostring()
return"square:width="+width":";


public class triangle entends (5)

double la;
double lb;
double lc;
public triangle(double la,double lb,double lc)
this.la=la;this.lb=lb;this.lc=lc;

public string tostring()(
return"triangle:sides="+la+","+lb+","+lc+":";

public double get area()
double s=(la+lb+lc)/2.0;
return math．sqrt(s^*(s-l

• a)^*(s-l
• b)^*(s-l
• c));