题目：定义Shape类表示一般二维图形。Shape具有抽象方法area和perimeter，分别计算形状的面积和周长。试定义一些二维形状类（如矩形、三角形、圆形等），这些均为Shape类的子类并计算出这些形状的面积和周长，打印输出相关信息。
代码：
//形状类
public abstract class Shape {
public abstract double area();
public abstract double perimeter();
}
//矩形类
public class Rectangle extends Shape { private double length;
private double width; public double getLength() {
return length;
} public void setLength(double length) {
this.length = length;
} public double getWidth() {
return width;
} public void setWidth(double width) {
this.width = width;
} @Override
public double area() {
return getLength() * getWidth();
} @Override
public double perimeter() {
return 2 * (getWidth() + getWidth());
}
}
//三角形类
public class Triangle extends Shape { private double a, b, c; public double getA() {
return a;
} public void setA(double a) {
this.a = a;
} public double getB() {
return b;
} public void setB(double b) {
this.b = b;
} public double getC() {
return c;
} public void setC(double c) {
this.c = c;
} @Override
public double area() {
double p = (getA() + getB() + getC()) / 2;
return Math.sqrt(p * (p - getA()) * (p - getB()) * (p - getC()));
} @Override
public double perimeter() {
return getA() + getB() + getC();
} }
//圆形类
public class Circle extends Shape { private double diameter; public double getDiameter() {
return diameter;
} public void setDiameter(double diameter) {
this.diameter = diameter;
} @Override
public double area() {
return Math.PI * Math.pow(getDiameter() / 2, 2);
} @Override
public double perimeter() {
return Math.PI * getDiameter();
} }
//测试代码
public class 测试 { public static void main(String [] args){
Rectangle rec = new Rectangle();
rec.setLength(10);
rec.setWidth(5);
double rec_area = rec.area();
double rec_perimeter = rec.perimeter();
System.out.println("矩形的面积："+rec_area+"，周长"+rec_perimeter); Triangle tri = new Triangle();
tri.setA(3);
tri.setB(4);
tri.setC(5);
double tri_area = tri.area();
double tri_perimeter = tri.perimeter();
System.out.println("三角形的面积："+tri_area+"，周长"+tri_perimeter); Circle cir = new Circle();
cir.setDiameter(10);
double cir_area = cir.area();
double cir_perimeter = cir.perimeter();
System.out.println("圆形的面积："+cir_area+"，周长"+cir_perimeter);
} }