题目内容：

java题:计算三角形和矩形的周长和面积,要求用接口,多态,继承,类四种不同方法分别写程序

优质解答

接口和继承都是多态的一种表现形式,所以一个小程序可以解决所以的问题!

马上写出来

package day0507;
public class Test {
    /**
     * @param args
     */
    public static void main(String[] args) {
        Shap triangle=new Triangle(3, 4, 8);//新建一个三边长为3,4,5的三角形
        Shap tri=new Triangle(3, 4, 5);
        Shap director=new Director(10, 20);//新建一个两边长为10,20的长方形
        System.out.println("三角形triangle的周长为："+triangle.longer());
        System.out.println("三角形triangle的面积为："+triangle.area());
        System.out.println("三角形tri的周长为："+tri.longer());
        System.out.println("三角形tri的面积为："+tri.area());
        System.out.println("该长方形的周长为："+director.longer());
        System.out.println("该长方形的面积为："+director.area());
    }
}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
package day0507;
public class Director implements Shap {
    double s1;
    double s2;
    //初始化一个长方形,并赋予该长方形两边长
    public Director(double s1,double s2){
        this.s1=s1;
        this.s2=s2;
    }
    //计算长方形面积
    public double area() {
        return s1*s2;
    }
    //计算长方形周长
    public double longer() {
        return 2*(s2+s2);
    }
}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
package day0507;
public class Triangle implements Shap {
    double s1;
    double s2;
    double s3;
    //初始化一个三角形对象,并赋予该三角形三边长
    public Triangle(double s1,double s2,double s3){
        if(isTri(s1, s2, s3)){
            this.s1=s1;
            this.s2=s2;
            this.s3=s3;
        }else{
        System.out.println("输入的三边长"+s1+"、"+s2+"、"+s3+"不能组成一个三角形,请重新输入三边长!");
        }
    }
    //判断是否是个三角形
    public boolean isTri(double s1,double s2,double s3){
        if(s1+s2<s3){
            return false;
        }
        if(s1+s3<s2){
            return false;
        }
        if(s2+s3<s1){
            return false;
        }
        return true;
    }
    //使用海伦公式计算三角形面积
    public double area() {
        double p=(s1+s2+s3)/2;
        return Math.sqrt(p*(p-s1)*(p-s2)*(p-s3));
    }
    //计算三角形周长
    public double longer() {
        return s1+s2+s3;
    }
}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
package day0507;
public interface Shap {
    public double area();
    public double longer();
}