我需要向用户询问他想绘制的图中有多少边,然后调用正确的构造函数来实例化该对象.
下面是我尝试使用IF语句来解决答案(或者我可以使用一个开关),但是我不知道这是否是最好的方法,可能是Java继承和多态.
所有的类都扩展了类图.
类别图：
--------------- Figure ---------------
^ ^ ^ ^
| | | |
| | | |
Circle Triangle Rectangle Exagone
主要类别：
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");
}
}
}
类别编号：
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
解决方法
工厂方法
你考虑过Factory Method Pattern吗？基本上,你有一个这样的方法：
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;
}
而让这种工厂方法做出决定.
