面向对象编程中的多态性和接口实现

第一题：定义接口Shape和实现该接口的Circle类和Rectangle类

提供接口Shape1和两个类Circle5和Rectangle5的实现。

在一个包内定义一个接口Shape，内含一个变量PI，一个方法:area()。定义Circle类和Rectangle类，实现接口Shape，重写area()方法
package shiyan7;
public interface Shape1 {
    //  内含一个变量PI，一个方法:area()。
    double PI=  3.14;
    double  area();
}

//Circle5圆
class Circle5 implements Shape1{
    double sum;
    double r;
    Circle5(double r){
        this.r=r;
    }

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

//Rectangle5 长方形
class Rectangle5 implements Shape1{
    double Length;
    double  Width;
    Rectangle5(double Length,double Width){
        this.Length = Length;
        this.Width  = Width;
    }
    @Override
    public double area() {
        return this.Length*this.Width;
    }
}

package shiyan7;
public class test {
    public static void main(String args[]){
        Circle5 S1= new Circle5(2);
        Rectangle5 S2= new Rectangle5(8,6);
        System.out.println("圆的面积："+S1.area());
        System.out.println("长方形的面积："+S2.area());
    }
}
 

在另一个包中定义测试类，创建Shape类型的数组

提供了Shape接口和几个实现该接口的类，以及一个Calculate类来计算面积。接下来，需要创建一个测试类TestShapes，它将使用Shape类型的数组来存储不同的图形对象，并计算它们的面积。

在另一个包中定义测试类，创建Shape类型的数组，调用数组元素的area()方法，输出相应信息。(也可以定义Calculate类，包含cal(Shapes)方法来计算s的面积。在main()方法中创建多个对象作为参数调用cal()方法，输出相应面积信息。)

package shiyan7_1;
public interface Shape {
    double PI = 3.14159;
    double area();
}

    public class  Circle5_1 implements Shape {
        private double radius;
        public  Circle5_1 (double radius) {
            this.radius = radius;
        }
        @Override
        public double area() {
            return PI * radius * radius;
        }
    }

public class Rectangle5_1 implements Shape {
    private double length;
    private double width;
    public Rectangle5_1(double length, double width) {
        this.length = length;
        this.width = width;
    }
    @Override
    public double area() {
        return length * width;
    }
}

public class ladder5_1 implements Shape {
    private double height;
    private double base1, base2;
    public ladder5_1(double base1, double base2, double height) {
        this.base1 = base1;
        this.base2 = base2;
        this.height = height;
    }
    @Override
    public double area() {
        return (base1 + base2) * height / 2;
    }
}

package shiyan7_2;

import shiyan7_1.Shape;

public class Calculate {
    public static double cal(Shape s) {
        return s.area();
    }
}

package shiyan7_2;
import shiyan7_1.Shape;
import shiyan7_1.Rectangle5_1;
import shiyan7_1.Circle5_1;
import shiyan7_1.ladder5_1;
public class TestShapes {
    public static void main(String[] args) {
       Shape[] shapes = new Shape[]
        {new Circle5_1 (5), new Rectangle5_1(8, 6)};
        for (Shape shape : shapes) {
            System.out.println("面积: " + shape.area());
        }}

添加新的图形梯形，并将其对象应用到第二题中

已经定义了ladder5_1类来表示梯形，并实现了Shape接口。需要在TestShapes类中添加一个梯形对象，并使用Calculate类的cal方法来计算其面积。

package shiyan7_2;
import shiyan7_1.Shape;
import shiyan7_1.Rectangle5_1;
import shiyan7_1.Circle5_1;
import shiyan7_1.ladder5_1;
public class TestShapes {
    public static void main(String[] args) {
 
        Shape circle = new Circle5_1(5);
        Shape rectangle = new Rectangle5_1(8, 6);
       Shape ladder = new ladder5_1(6,10,8);
       System.out.println("圆的面积是: " + Calculate.cal(circle));
       System.out.println("长方体的面积是: " + Calculate.cal(rectangle));
       System.out.println("梯形的面积是: " + Calculate.cal(ladder));
    }