Question

早上好！我有一个非常快速的问题。这是关于从主程序中的数组中的子类打印数据。拜托我，我对此很新。

程序应打印形状的周长，面积和平均长度，该形状在超类“Shape”的子类中定义

但所有打印都是“形状”。

我知道它只是在语法上的一个调整，但已经尝试了几个小时来找到问题所在。我想知道你们中是否有人可以给我一些指示？谢谢，非常感谢您的帮助。

→为了便于理解，我粘贴了我的程序的4个部分，

Main（用于收集用户输入并打印结果）
形状超类（主要用于定义周长和面积）
平行四边形界面（基本上是边长的平均值）
Square子类（处理所有信息的地方）

主要：

package shape;

import java.util.ArrayList;
import java.util.Scanner;

@author Fulltime

public class MainExecute {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        ArrayList<Shape> list = new ArrayList<>();
        Triangle t;
        Square s;
        Trapezoid r;

        while(true){
            Scanner Choice = new Scanner(System.in);
            System.out.println("Enter a shape: ");
            String choice = Choice.nextLine();
            if(choice.equalsIgnoreCase("STOP")){
                break;
            }
            else if(choice.equalsIgnoreCase("triangle")){
                System.out.print("Enter base of triangle: ");
                double base = Choice.nextDouble();
                System.out.print("Enter height of triangle: ");
                double height = Choice.nextDouble();
                t = new Triangle(base, height);
                list.add(t);
            }
            else if(choice.equalsIgnoreCase("square")){
                System.out.print("Enter side of square: ");
                double side = Choice.nextDouble();
                s = new Square(side);
                list.add(s);
            }
            else if(choice.equalsIgnoreCase("trapezoid")){
                System.out.print("Enter length1 of trapezoid: ");
                double length1 = Choice.nextDouble();
                System.out.print("Enter length2 of trapezoid: ");
                double length2 = Choice.nextDouble();
                System.out.print("Enter height of trapezoid: ");
                double height = Choice.nextDouble();
                r = new Trapezoid(length1, length2, height);
                list.add(r);
            }
        }
        Shape q;
        System.out.println("Shapes: ");
        for(int i = 0; i <list.size(); i++){
            q = list.get(i);
            System.out.println(q.getClass().getName());
            if(q.getClass().getName().equalsIgnoreCase("Triangle")){
                t=(Triangle)q;
                System.out.println("Perimeter: " + t.getPerimeter());
                System.out.println("Area: " + t.getArea());
            }
            if(q.getClass().getName().equalsIgnoreCase("Square")){
                s=(Square)q;
                System.out.println("Perimeter: " + s.getPerimeter());
                System.out.println("Area: " + s.getArea());
                System.out.println("Average length of sides: " + s.getAverage());
            }
            if(q.getClass().getName().equalsIgnoreCase("Trapezoid")){
                r=(Trapezoid)q;
                System.out.println("Perimeter: " + r.getPerimeter());
                System.out.println("Area: " + r.getArea());
                System.out.println("Average length of sides: " + r.getAverage());
            }
        }    
    }        
}

形状超类

package shape;
import java.util.*;

public abstract class Shape {

    public abstract double getPerimeter ();
    public abstract double getArea ();

    public double Perimeter;
    public double Area;

    public void displayInfo(){
        //System.out.println("Perimeter: " + this.getPerimeter());
        //System.out.println("Area: " + this.getArea());
    }        
}

平行四边形界面

package shape;

@author Fulltime

public interface Parallelogram {
    public double getAverage();
}

Square Subclass

package shape;
import static java.lang.Math.*;

@author Fulltime

public class Square extends Shape implements Parallelogram {

    public Square(){}

    @Override
    public double getPerimeter (){
        Perimeter = side * 4;    
        return Perimeter;
    }

    @Override
    public double getArea (){
        Area = side * side;   
        return Area;
    }

    @Override
    public double getAverage(){
        double Sides;
        Sides = (this.side + this.side + this.side + this.side) / 4;
        return Sides;
    }

    public double side;

   /**
    * @return the side
    */
    public double getSide() {
        return side;
    }

   /**
    * @param side the side to set
    */
    public void setSide(double side) {
        this.side = side;
    }

    public Square (double side){
        this.side = side;        
    }

    public void printSquare(){
        System.out.println("The Perimeter of this shape is " + getPerimeter());
        System.out.println("The Area of this shape is " + getArea());
        System.out.println("The Average Length of this shape's sides is " + getAverage());
    }   
}

Answer 1

使用getSimpleName()返回没有包资格的类名。

 if(q.getClass().getSimpleName().equalsIgnoreCase("Triangle")){

 }else if(..) // Also use else-if

或者您可以使用instanceof运算符

   if(q instanceof Triangle){
      //logic here
   }else if(..)

现在作为一个注释，这不是一个很好的OO设计，使用if-else，你应该重新考虑重新设计你的模型。

例如make displayInformation abstract，那么所有具体的子类都必须覆盖它。

abstract class Shape{

 public abstract void displayInformation(); 
}

三角

public class Triangle extends Shape implements whatyouwant {


 @Override 
 public void displayInformation(){
   System.out.println("Perimeter: " + this.getPerimeter());
   System.out.println("Area: " + this.getArea());
 }

}

广场：

public class Square extends Shape ..{

 @Override
 public void displayInformation(){
     System.out.println("Perimeter: " + this.getPerimeter());
            System.out.println("Area: " + this.getArea());
            System.out.println("Average length of sides: " + this.getAverage());
 }

}

那么在您的主要课程中，您不必编写任何if-else代码，只需看到polimorphism magic。

  for(Shape shape : list){//use enhanced loop
     shape.displayInformation();
  }

使用Java中的子类从main打印数据

1 个答案: