根据用户输入决定构造函数调用

我需要询问用户他想要绘制的图有多少边,然后调用正确的构造函数来实例化对象.

下面是我尝试使用IF语句解决答案(或者我可以使用开关),但我不知道这是否是最好的方法,可能是Java继承和多态.

所有类都扩展了类图.

课程图:

      --------------- Figure ---------------
      ^         ^             ^            ^
      |         |             |            |
      |         |             |            |
   Circle    Triangle      Rectangle     Exagone

主类:

import java.util.Scanner;

class Draw {

   static void main(String[] args){

       Scanner userInput = new Scanner(System.in);
       int num_sides;

       //user input
       System.out.println("How many sides has the figure you want to draw?");   
       num_sides = userInput.nextInt();


       //---> deciding what constructor to call with if statements

       if(num_sides == 0){
          Figure f1 = new Circle();
       }
       else if(num_sides == 3){
          Figure f1 = new Triangle(); 
       }
       //...
       else{
          System.out.println("Error. Invalid sides number");
       }


   }
}

课程代码:

class Figure{

    private int sides;

    public Figure(int num_sides){
       sides = num_sides;
    }
}


class Circle extends Figure{

   public Circle(){
      super(0);
   }

}

//... all the other classes has the same structure of Circle

Caleb Brinkm.. 10

工厂方法

您是否考虑过工厂方法模式？基本上,你有一个类似这样的方法:

public Figure createInstance(int numSides) {
    Figure figure = null;

    switch(numSides) {
    case 0:
        figure = new Circle();
        break;
    case 3:
        // etc...
        // Make a case for each valid number of sides
        // Don't forget to put a "break;" after each case!
    default:
        // Not a valid shape; print your error message
    }
    return figure;
}

让工厂方法做出决定.

工厂方法

您是否考虑过工厂方法模式？基本上,你有一个类似这样的方法:

public Figure createInstance(int numSides) {
    Figure figure = null;

    switch(numSides) {
    case 0:
        figure = new Circle();
        break;
    case 3:
        // etc...
        // Make a case for each valid number of sides
        // Don't forget to put a "break;" after each case!
    default:
        // Not a valid shape; print your error message
    }
    return figure;
}

让工厂方法做出决定.