问题

如何实现类似这样的功能？我想要接受类似 `Circle 10` 或者 `Rectangle 20 30` 这样的命令行参数，并创建相应类的对象。

class Circle{
    //这里是一些代码
}

class Rectangle{
    //这里是一些代码
}

public class Perimeter{
    public static void main(String[] args) {
        for(int i=0; i<args.length; i++){
            String shape = args[i];
            Shape currShape;

            if(shape.equals("Circle")){
                double radius = Double.parseDouble(args[i+1]);
                currShape = new Circle(radius);
                System.out.println(currShape.getPerimeter());
                i++;
            }
            else if(shape.equals("Rectangle")){
                double length = Double.parseDouble(args[i+1]);
                double width = Double.parseDouble(args[i+2]);
                currShape = new Rectangle(length, width);
                System.out.println(currShape.getPerimeter());
                i += 2;
            }
        }
    }
}

注意：上述代码中的 Shape 类需要根据需要自行定义，并确保 Circle 和 Rectangle 类中有计算周长的方法（例如 getPerimeter）。

class Circle{
    //Some lines here
}

class Rectangle{
    //Some lines here
}

public class Perimeter{
    public static void main(String[] args) {
        for(int i=0; i< args.length; i++){
            String shape = args[0];
            shape curr_shape = new shape();
            System.out.println(curr_shape.getPerimeter( <arguments> ));
        }
    }
}

答案1

得分: 2

可以使用Class.forName()和反射来创建一个实例，就像@Milgo提议的那样，但我建议创建一个简单的switch/case语句。你的任务看起来像是一些训练，所以这可能是你的最佳选项。

Object form;
switch (type) {
  case "Circle":
    form = new Circle();
    break;
  case "Rectangle":
    form = new Rectangle();
    break;
}

Object form;
switch (type) {
  case "Circle":
    form = new Circle();
    break;
  case "Rectangle":
    form = new Rectangle();
    break;
}

答案2

得分: 1

以下是您要翻译的内容：

虽然您可以使用反射（即黑魔法）来实现，但如果所有形状都具有相同的构造函数签名，比如 List<Double>（其中包括像您的示例中的整数） ，您可以使用最少的代码来完成：

private static Map<String, Function<List<Double>, Shape>> factories = 
    Map.of("Circle", Circle::new, "Rectangle", Rectangle::new); // 等等

public static Shape createShape(String input) {
    String[] parts = input.split(" ");
    String name = parts[0];
    List<Double> dimensions = Arrays.stream(parts)
      .skip(1) // 跳过名称
      .map(Double::parseDouble) // 将字符串转换为双精度数
      .collect(Collectors.toList());
    return factories.get(name).apply(dimensions); // 调用构造函数
}

interface Shape {
    double getPerimeter();
}

static class Rectangle implements Shape {
    private double height;
    private double width;

    public Rectangle(List<Double> dimensions) {
        height = dimensions.get(0);
        width = dimensions.get(1);
    }

    @Override
    public double getPerimeter() {
        return 2 * (height + width);
    }
}

static class Circle implements Shape {
    double radius;

    public Circle(List<Double> dimensions) {
        radius = dimensions.get(0);
    }

    @Override
    public double getPerimeter() {
        return Math.PI * radius * radius;
    }
}

private static Map<String, Function<List<Double>, Shape>> factories = 
Map.of("Circle", Circle::new, "Rectangle", Rectangle::new); // etc
public static Shape createShape(String input) {
String[] parts = input.split(" ");
String name = parts[0];
List<Double> dimensions = Arrays.stream(parts)
.skip(1) // skip the name
.map(Double::parseDouble) // convert String terms to doubles
.collect(toList());
return factories.get(name).apply(dimensions); // call constructor
}
interface Shape {
double getPerimeter();
}
static class Rectangle implements Shape {
private double height;
private double width;
public Rectangle(List<Double> dimensions) {
height = dimensions.get(0);
width = dimensions.get(1);
}
@Override
public double getPerimeter() {
return 2 * (height + width);
}
}
static class Circle implements Shape {
double radius;
public Circle(List<Double> dimensions) {
radius = dimensions.get(0);
}
@Override
public double getPerimeter() {
return (double) Math.PI * radius * radius;
}
}