题目求源码，不太会写，求源码⋯⋯

⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯⋯

仅供参考

public class ShapeTest {

    abstract class Shape{
        public abstract double area();
        public abstract double perimeter();
    }

    class Rect extends Shape{

        private double width;
        private double length;

        public Rect(double w,double l){
            width = w;
            length = l;
        }
        @Override
        public double area() {
            return width*length;
        }

        @Override
        public double perimeter() {
            return 2*(width+length);
        }
    }

    class Circle extends Shape{

        private double r;
        public Circle(double r){
            this.r = r;
        }
        @Override
        public double area() {
            return Math.PI * r * r;
        }

        @Override
        public double perimeter() {
            return 2 * Math.PI * r;
        }
    }
    public static void main(String[] args){

        ShapeTest st = new ShapeTest();

        Rect r = st.new Rect(2,3);
        System.out.println("矩形的周长为："+r.perimeter());
        System.out.println("矩形的面积为："+r.area());

        Circle c = st.new Circle(1); //单位圆
        System.out.println("圆形的周长为："+c.perimeter());
        System.out.println("圆形的面积为："+c.area());
    }
}

定义一个抽象类Shape ，两个抽象方法，area ， perimeter ，定义矩形类Rectangle ,继承抽象类 ，实现两个抽象方法,定义两个属性height ,width；
public int area(){
return height*width;
}
就这样做

考察的是面向对象的抽象思维，抽象父类，以及它对应的各个子类。建议先好好研究下课本上的例子，然后仿造例子思考该题目。

public abstract class Shape {
    public abstract double area();
    public abstract double perimeter();
} 

 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());
    }
}

 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();
    }

}

 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();
    }

}

 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);
    }

}

考察抽象类的使用。也可以使用接口进行操作。

// 抽象类
public abstract class Shape {

void area() {}

void perimeter() {}

}

public class TestCycle extends Shape {

// 半径
private int r;

public TestCycle(int r) {

    this.r = r;

}

@Override
public void area() {

    System.out.println("圆形的面积: " + Math.PI * r * r);
}

@Override
public void perimeter() {

    System.out.println("圆形的周长: " + 2 * Math.PI * r);

}


public static void main(String args[]){

    int r = 5;
    TestCycle tc = new TestCycle(r);
    tc.area();
    tc.perimeter();

}
// 圆形的面积: 78.5
// 圆形的周长: 31.4

}

// 矩形
public class TestRectangle extends Shape {

private int chang;

private int kuan;

public TestRectangle(int c, int k) {

    this.chang = c;

    this.kuan = k;
}

@Override
public void area() {

    int area = chang * kuan;

    System.out.println("矩形的面积: " + area);
}

@Override
public void perimeter() {


    int perimeter = (2*chang) * (2*kuan);

    System.out.println("矩形的周长: " +perimeter);

}


public static void main(String args[]){

    int c = 5;
    int k = 2;
    TestRectangle tc = new TestRectangle(c, k);
    tc.area();
    tc.perimeter();

}

// 输出 面积是  10
// 输出 周长是  40

}